实验流体力学

Development and experimental analysis of circular foil pressure-heat flux gage

ZHU Xinxin , YANG Yuanjian etc.

doi: 10.11729/syltlx20230044

[Abstract](19) [FullText HTML](6) [PDF 9428KB](2)

Abstract:
Based on the demand of heat flux measurement in the continuous test of vehicle changing orbit, the circular foil pressure-heat flux gage that also can get pressure is developed on the basis of the traditional Gardon gage. The thermal radiation calibration test, the different plate comparison tests in the arc-heated wind tunnel, and numerical calculation analysis are carried out. The results show that the new circular foil pressure-heat flux gage can simultaneously get heat flux and pressure at the same point of the plate model in the multistate continuous arc-heated wind tunnel test. Repeatability accuracy of heat flux and pressure measurement are about 3.6% and 1.9% respectively. Compared with the slug calorimeter, the heat flux value measured by the circular foil pressure-heat flux gage is lower than 14.7%. There are two main reasons for the discrepancy. On one hand, the gage sensitivity coefficient decreases in the convective measurement environment; on the other hand, the incident heat flux of the gage decreases because the temperature of the constantan foil is relatively high so that a local hot spot is formed. Finally, some suggestions for the use of the new circular foil pressure-heat flux gage and traditional Gardon gage are given.

Multi-wavelength synthetic aperture rainbow refractometer

WANG Xinhao , WU Yingchun etc.

doi: 10.11729/syltlx20230026

[Abstract](14) [FullText HTML](7) [PDF 6682KB](2)

Abstract:
Against the increasing requirement of large-scale conditions, there is more demand of the measurement instruments. As an efficient approach of measuring cloud droplets, the measurement distance of the rainbow refractometry is generally less than 50 cm owing to the limitation of the aperture of the imaging system. The synthetic aperture rainbow refractometry is proposed to achieve long distance droplet measurement. Laser beams of multiple wavelengths are used to irradiate droplets and multiple rainbow signals are generated. The multiple rainbow signals are collected and combined into one signal and then inversed to obtain the droplet parameters. In this way, the measurement distance of the rainbow refractometry is increased to around 1.5 m, which breaks the aperture limit of the rainbow refractometry and enlarges its applicability. Based on this technique, the multi-wavelength synthetic aperture rainbow refractometer is developed and suitable for parameter measurement of droplets in the central region of large-scale facilities with instruments located outside. The synthetic aperture rainbow refractometry is verified to achieve long distance droplet measurement. The feasibility and accuracy of the multi-wavelength synthetic aperture rainbow refractometer were proved through experimental tests of water and ethanol droplets with different sizes and refractive indices. The sizes of water and ethanol droplets were within the range from 100 to 200 μm. The droplet size and refractive index uncertainties were within 5 μm and 8 × 10⁻⁴, respectively. Therefore, the multi-wavelength synthetic aperture rainbow refractometer is no longer limited by the aperture size and can be applied to larger industrial scenarios, achieving the multi-parameters droplet measurement of size, refractive index, and so on.

Experimental study of the mechanism of drag reduction in turbulent boundary layers on the superhydrophobic structured wall with microstructure

LIU Zhaoyang , WANG Xinwei etc.

doi: 10.11729/syltlx20220016

[Abstract](17) [FullText HTML](8) [PDF 7996KB](3)

Abstract:
The drag reduction mechanism of the wall turbulent boundary layer with superhydrophobic micro-riblets and micro-convex posts is studied experimentally. The instantaneous velocity field in the turbulent boundary layer of the hydrophilic wall, superhydrophobic micro-riblets wall and micro-convex posts wall is measured by high time resolution particle image velocimetry (TRPIV). The frictional shear stress of the three kinds of walls is compared and analyzed. It is found that the superhydrophobic walls achieve drag reduction effect. However, the drag reduction rate of the superhydrophobic micro-riblets wall is higher than that of the superhydrophobic micro-convex posts wall, and the drag reduction rate of the superhydrophobic micro-riblets wall is 13.8%, while the drag reduction rate of the superhydrophobic micro-convex posts wall is 10.2%. Through comparison and analysis on the three kinds of wall corresponding average velocity profile in the turbulent boundary layer, turbulence intensity and Reynolds shear stress profile, it is found that the fluid indeed has sliding speed in the superhydrophobic wall, and in the area of the same normal height at $15 < {y^ + } < 100$, the streamwise turbulence intensity corresponding to the hydrophilic wall, superhydrophobic micro-riblets and micro-convex posts wall decreases successively. At the same time, in the area of the same normal height at $30 < {y^ + } < 80$,the wall-normal turbulence intensity of the superhydrophobic micro-convex posts, hydrophilic wall and superhydrophobic micro-riblets wall decrease successively. Over the whole wall-normal height, the maximum values of Reynolds shear stress on the hydrophilic wall, superhydrophobic micro-convex posts and micro-riblets wall decrease successively. Based on the conditional sampling and phase averaging of the spanwise vortex identified by the ${\Lambda _{{\text{ci}}}}$criterion, it is found that the amplitude of the fourth quadrant event induced by the spanwise vortex of the superhydrophobic micro-riblets wall weakens nearby at ${y^{\text{ + }}} \approx 63$, which leads to the intensity of its sweep events decreasing, and then the drag reduction is realized. In order to further analyze the turbulent fluctuation energy, the instantaneous fluctuation velocity of the whole turbulent boundary layer is summed in time and over the streamwise-normal space by using Proper Orthogonal Decomposition and it is dimensionless to characterize the fluctuation degree of the flow field. The results show that the spanwise slip characteristics of the superhydrophobic micro-convex posts increase the drag and weaken the drag reduction effect caused by the streamwise slip. The streamwise slip characteristics of the superhydrophobic micro-riblets wall can effectively suppress turbulence fluctuation and achieve better drag reduction effects.

Propagation characteristics of dynamic feature in transonic cavity shear layer

ZHOU Fangqi , WANG Xiansheng etc.

doi: 10.11729/syltlx20230066

[Abstract](39) [FullText HTML](21) [PDF 6924KB](3)

Abstract:
In the shear layer of the open cavity flow, the vortex interacts with the pre-transmission sound wave, causing self-sustaining oscillation. For a cavity model with a length-to-depth ratio of 7, the dynamic characteristics of the shear layer in the cavity were tested under the incoming flow condition of Mach number 0.9 by the pulsating pressure measurement technology, and the propagation law of the modal noise in the shear layer is revealed by the spectrum analysis and cross-correlation analysis. The results show that the superposition of the monotonically increasing broadband noise and cosine-like modal noise in the shear layer causes the wave-rise characteristics of the overall dynamic of the shear layer. The modal noise propagates in the reverse flow direction, its velocity is also cosine-like, and the change trend is consistent with the modal noise amplitude. Combined with the Rossiter mode estimation theory, it is revealed that the interaction between modal sound waves and vortices of the same frequency produces a standing wave-like phenomenon, resulting in periodic changes in the power spectrum density and propagation velocity of the modal noise along the flow direction.

Experimental investigation of turbulence intensity measurement in continuous transonic wind tunnel

ZHU Bo , CHEN Jiming etc.

doi: 10.11729/syltlx20220034

[Abstract](46) [FullText HTML](30) [PDF 7600KB](4)

Abstract:
The constant temperature anemometer is used for turbulence intensity measurement from the entrance of the heat exchanger to the test section in a 0.6 m continuous transonic wind tunnel. Two dimensional hot wire probes were rotated to measure the three dimensional turbulence intensity in the flow field from the entrance of the heat exchanger to the exit of the setting chamber. One dimension hot wire probes were used for turbulence intensity measurement in transonic flow of test section, with the method of continuous varying hot wires over heating ratio, where the maximum testing flow velocity was Ma1.5. Test results show that, the heat exchanger and the setting chamber paly important roles in damping turbulence intensity, each of which could reduce the turbulence intensity by more than 90%; when the screens in the setting chamber are added from 3 to 5 layers, the turbulence intensity of setting chamber could be decreased by 50%, and could be decreased by 17% in the test section; using the continuous varying hot wires over heating ratio method, the fluctuation diagrams and turbulence intensity are acquired in the test section. The fluctuation curve is of the straight line type at Mach number 0.4, and the fluctuation curve is of the hyperbola type at Mach number 0.7, which present the fluctuation characteristics in the flow field. Experiment results are useful for flow turbulence evaluation and optimization in the continuous transonic wind tunnel.

Experimental investigation on growth profiles of microalgae with different flow conditions in photo-bioreactors

ZHANG Ting , FENG Aiguo etc.

doi: 10.11729/syltlx20220028

[Abstract](31) [FullText HTML](45) [PDF 7861KB](10)

Abstract:
Well-designed Photo-bioreactors (PBR) support high-efficiency biomass production. Methods: Flow fields of plat-plate PBR are experimental investigated with a time-resolved particle image velocimeter (TR-PIV). Results: Microalgae flow around sets of baffles improves performance of Chlorella vulgaris growth. Conclusion: The PIV-based flow visualization method benefits microalgae PBR designs, implements of high-density cultivations. The PBR structures proposed in this paper is of great supports to design and high productivity of bio-products with high added-values.

Review of slat noise mechanism and control in high-lift devices

WEI Renke , LIU Yu

doi: 10.11729/syltlx20230017

[Abstract](80) [FullText HTML](26) [PDF 11932KB](17)

Abstract:
During aircraft landing, the slat of high-lift devices is an important source of airframe aerodynamic noise. In recent decades, a large number of wind tunnel tests on slat noise have been carried out domestically and abroad. A deep understanding has been achieved on the characteristics and mechanisms of slat noise, and many attempts have been made in flow control and noise reduction technologies. Slat noise mainly includes low-frequency broadband noise, low-frequency discrete tonal noise, and high-frequency tonal noise. In this paper, the main research progress of wind tunnel testing on two-dimensional airfoil slat noise is reviewed and analyzed, and the generation mechanisms of the three slat noise components are introduced in detail. There are three main categories of control methods for slat noise. The first is the fairing method represented by the slat cove filler, which removes or limits the generation of recirculation flow and hence significantly reduces noise. The second is applied at the slat cusp to interfere with the formation of coherent structures in the shear layer. From the perspective of engineering feasibility, the third category is to optimize the slat slot and structural parameters or to adopt new configurations with leading edge droop as an example. In summary, in order to achieve efficient noise control technologies, it is necessary to deeply understand the complex phenomena in the shear layer flow of the slat cove, such as the fluid-acoustic coupling and its interference with the slat trailing edge, through advanced testing methods and experimental schemes.

Investigation on error correction method of five-holes probes used in flow field with large velocity gradient

XIE Jinwei , GUO Tao etc.

doi: 10.11729/syltlx20230009

[Abstract](51) [FullText HTML](30) [PDF 6176KB](9)

Abstract:
In order to explore the distortion characteristics of the five-holes probe under a large gradient flow field (ΔV/V), a data processing method for correcting the measurement error caused by the velocity gradient is established. An investigation based on the five-holes probe principle is employed to reveal the effect of the flow angle and velocity gradient on the measurement error. A correct method is proposed and verified by the experiment. The results show: the measurement error of the velocity value is far less than that of the flow angle and can be ignored in ordinary range (ΔV/V = ± 0.3 in this paper). The measurement error of the flow angle is usually notable. The error is affected by the velocity gradient and flow angle. The results of the experiment confirm that the correction method based on the velocity gradient and flow angle can reduce the angle error effectively.

The development of the movable Solid Wall Test Section for the 5.5 m × 4 m acoustic wind tunnel

YANG Wenguo , SHI Yan etc.

doi: 10.11729/syltlx20220061

[Abstract](62) [FullText HTML](30) [PDF 11568KB](4)

Abstract:
According to the design indexes and functional requirements of the movable Solid Wall Test Section for 5.5 m × 4 m acoustic wind tunnel, this report presents the Design Project of overall scheme. The simulation calculation is carried out around the strength, stiffness and mode of the frame in the movable solid wall test section. The key technologies of positioning and locking, lifting mechanism, replaceable lower wall panel and adjustable opening side wall panel are studied in detail. At the same time, specific solutions are provided for the key problems in its processing and assembly process. The above research contents have important reference value for the design of closed test section of large acoustic wind tunnel of the same type.

A wind tunnel investigation of the helicopter vortex ring state boundary

WANG Chang , MA Shuai etc.

doi: 10.11729/syltlx20220055

[Abstract](52) [FullText HTML](51) [PDF 7882KB](3)

Abstract:
The helicopter vortex ring state boundary is systematically analyzed and studied in this paper. Firstly, the causes of vortex ring state accidents are analyzed, and the physical mechanisms in flight characteristics, rotor performance, rotor inflow, and vortex structure are expounded. The formation of concentrated vortex causes the induced inflow to dominate the vertical inflow on the rotor disk, causing negative damping of rotor thrust and loss of rotor performance, and as a result the instability of subsidence motion. Then, the differences and applicability of various vortex ring state boundaries are compared, the problems of the existing boundary prediction models with strong subjectivity in modeling methods and high dispersion of test data are concluded, and improvement ideas are proposed. Finally, on the basis of the above knowledge, a rotor wind tunnel test to simulate the descending flight was designed and carried out. The test results show that the rotor thrust negative damping, thrust loss and power subsidence phenomenon are presented in the vortex ring state, the rotor thrust loss is up to 30%, and the required power is about 160% of the hovering power when the rotor generates the same thrust as hover; using the negative damping of rotor thrust and the loss of thrust performance, which are concerned in the practice of flight emergency, as the defining index, the discrete points of the critical velocity at vortex ring state boundary are extracted from the test results; in the construction of the vortex ring state boundary model, the strength of the horizontal inflow, the vertical inflow and the induced inflow on the rotor tip vortex is distinguished, and the correction of the momentum theory under different advance ratios and the difference of the rotor tip vortex motion threshold are taken into account. On the basis of the model parameters determined by the least squares method based on the test values, a semi-empirical vortex ring state boundary prediction model is established, and the model is in good agreement with the wind tunnel test results and in line with the trend of flight test results. The understanding of the vortex ring state and the prevention of accidents in this study have practical significance.

The aerodynamic heating consistency study between CFD and experiment for air-breathing integrated vehicle

ZHANG Xuhui , WANG Zhaowei etc.

doi: 10.11729/syltlx20220041

[Abstract](43) [FullText HTML](31) [PDF 7841KB](7)

Abstract:
In order to improve the accuracy of simulation and obtain the aerodynamic heating consistency of the prediction method for the typical integrated design of the aircraft forebody model, experiments were carried out at FD−20a shock tunnel under the condition of Ma=6, Re=1.14×10⁷～2.98×10⁷m⁻¹, α=0°～8°. Numerical simulations were applied through the compressible Navier−Stokes equation implemented with the finite volume method, Roe’s flux difference splitting scheme, LU−SGS spatial method and Spalart–Allmaras (SA) turbulence model. Simulation results were compared with the experimental data to validate the prediction methods. Results show that with the increase of the complexity and disturbance intensity, the heat flux consistency decreases. The compression surface flow was dominated by the attached flow and small separation, where relative good consistency was found between the simulation and experimental data with the average difference being about 22.3%. The throat boundary layer was interfered by shock waves, and 43.5% difference was found between the heat flux simulation and experimental data. The heat flux difference in the isolation section increased to 31.8%. When the oblique shock impinged on the subsonic part of the bow shock and three dimensional flow patterns were obvious, the difference of heat flux reached the maximum of around 100% in three dimensional areas. Mesh, simulation methods and unsteady characteristics are concluded as the reasons for heat flux consistency decreasing along the airflow.

Experimental study on influence of incoming total temperature on hypersonic boundary layer transition

LI Qiang , WAN Bingbing etc.

doi: 10.11729/syltlx20220081

[Abstract](51) [FullText HTML](29) [PDF 8505KB](5)

Abstract:
Wall-temperature-ratio/temperature is a parameter that needs attention in the study of hypersonic boundary layer transition. The boundary layer transition experiment was carried out in CARDC Φ2 m shock tunnel, the model is a 7° half-angle cone model with the nosetip bluntness of 0.05mm, the Mach number is 9.86 and 9.97, the unit Reynolds number is 8.9 × 10⁶/m and 8.4 × 10⁶/m, and the total temperature is 1332.2 K and 956.6 K, respectively. Under the conditions of approximately the same Mach number, Reynolds number, noise level and wall temperature, the effect of the total temperature of the wind tunnel on the transition of the hypersonic boundary layer is studied. The heat flux sensor is used to measure the transition position and the high frequency fluctuation pressure sensor is used to measure the fluctuation characteristics of the boundary layer. The experimental results are compared with the transition prediction results of the γ−Re_θ−MT model and the linear stability theory results, respectively. The heat flux distribution results of the cone calculated by the transition model are in good agreement with the wind tunnel test results, and the transition positions obtained experimentally and theoretically are basically the same, indicating that the numerical calculation method of the transition model has high reliability. The pressure fluctuation results measured by the PCB sensor and the theoretical analysis results of the linear stability are mutually confirmed, showing the second mode wave spectrum characteristics of the two cases of high and low total temperature under wind tunnel conditions.

Experimental investigation on the flow-induced vibration of a riser subjected to the combination of internal liquid flow and external sheared flow

GAO Yue , ZHU Hongjun etc.

doi: 10.11729/syltlx20220033

[Abstract](55) [FullText HTML](31) [PDF 7893KB](7)

Abstract:
Flexible risers which are commonly applied to transport submarine resources have been widely utilized in offshore engineering. The intricate flow-induced vibration （FIV） of flexible risers is easily encountered with the presence of both internal and external flows. Once the riser fatigue failure occurs, it causes serious environmental pollution. In this work, a series of tests were conducted in a recirculating water flume to investigate the dynamic behavior of a flexible catenary riser under the combination of the internal liquid water flow and the external shear current. A non-intrusive high-speed imaging technique was employed to record the vibration displacement varying along the riser span. The reduced velocity and the internal flow velocity ranged from 3.55 to 44.69 and from 0.674 m/s to 1.651 m/s, respectively. The influence of the internal flow velocity on the dynamic response was examined. The experimental results including the spatial-temporal response amplitude and frequency as well as the mode evolution of out-of-plane were analyzed. The results show that the response is enhanced with increasing internal flow velocity except for the mode transition cases. In addition, the existence of the internal flow leads to the earlier occurrence of the mode transition. When the lock-in occurs in the vortex-induced vibration of the flexible riser, the amplitude of the flexible riser is magnified with increasing internal velocity, while the new mode response is not triggered. There is a new mode response occurring in the mode transition cases.

Study of splash characteristics and spreading mechanism of liquid droplets impacting walls at low temperature

LEI Jilin , GOU Yao etc.

doi: 10.11729/syltlx20220147

[Abstract](60) [FullText HTML](38) [PDF 7310KB](1)

Abstract:
The phenomenon of droplets impacting on the cold wall is one of the key factors leading to the deterioration of aircraft wing icing, wire icing and cold start of internal combustion engine. Droplet splashing and spreading characteristics are the main causes of the above problems. High-speed photography was used to study the splashing and spreading characteristics of n-dodecane droplets striking aluminium plates at different temperatures. The results show that as the wall temperature decreased (20 ℃ to −40 ℃) the droplet fragmentation threshold is significantly reduced, the secondary droplet diameter and number increase significantly, and the spreading speed and maximum spreading distance of the attached liquid film decrease significantly. In this study, a new dimensionless spreading coefficient (β_T = (D/D₀)/Re_T^0.07) and a new spreading model (β_T = 1.76τ^0.5) were constructed for the kinematic characteristics of the fast spreading phase of the liquid film attached to the low temperature wall, considering the effect of wall temperature on the viscous forces. The spreading model not only enables an accurate description of the liquid film spreading process under different insertion conditions and wall temperatures, but also widens the range of application of the model from 0.1 ≤ τ ≤ 1.0 to 0.1 ≤ τ ≤ 1.5, allowing the resulting low temperature spreading model to accurately describe changes in the spreading pattern of the liquid film over a longer period of time.

Application of a calibration-free wavelength modulation spectroscopy in the diagnosis of high-enthalpy flow field

CHEN Wei , WANG Lei etc.

doi: 10.11729/syltlx20220099

[Abstract](42) [FullText HTML](33) [PDF 8055KB](3)

Abstract:
Parameters of the high-temperature gas in the high-enthalpy flow field arean important basis for analyzing the thermochemical characteristics of the high-enthalpy flow and its interaction mechanism with exothermic materials. However, due to the high temperature of the flow field and severe chemical reaction, the measurement signals of these parameters are difficult to calibrate, which makes quantitative measurement difficult all the time. Wavelength Modulation Spectroscopy (WMS) is a kind of Tunable Diode Laser Absorption Spectroscopy (TDLAS), which has stronger anti-interference ability and is more suitable for complex environment application compared with the direct absorption method. A calibration-freed data processing method of WMS has been realized by fitting the measured harmonic signal with the theoretical harmonic signal, and applied in the diagnosis of the high frequency induction plasma flow and thearc-heated flow. The results show that the temperature and electronic density in the plasma flow resolved by the WMS are very close to those measured by the direct TDLAS, and the relative error of the specific enthalpy in the arc-heated flow between the WMS and the energy balance method is about 10%, which indicates that the free-calibrated WMS is reliable and can be used as an effective tool in the quantitative measurement of the high-enthalpy flow.

Investigation on full field three-dimensional flow in a multi-pass channel based on Magnetic Resonance Velocimetry (MRV)

DUAN Jingtian , WANG Zirui etc.

doi: 10.11729/syltlx20230015

[Abstract](50) [FullText HTML](43) [PDF 9479KB](2)

Abstract:
Magnetic Resonance Velocimetry (MRV) has the unique advantage of rapidly measuring three-dimensional three-component (3D3C) velocity distributions in complex structures, meanwhile it doesn’t need complex optical systems and tracer particles. MRV has become an important means for the study of full flow field. The full-field 3D velocity distribution in a three-pass serpentine channel was measured successfully. Results indicate that MRV has the ability to accurately resolve the complex 3D flow characteristics in the multi-pass channel. From the full-field 3D velocity distribution, it could be found that the flow near the bends has complex 3D features. The secondary flow is obvious on the cross-sections near the bends, which directs from the center of the channel to the upper and lower end walls. Dean vortices were observed in the right-angle bend, U-shaped bend and their downstream clearly. Flow driven by the Dean vortex directs to the upper and lower end walls, which is believed to be the essential reason for local heat transfer enhancement.

Simulation and experimental study of inlet heating simulator for a turbofan engine

LIU Guoyin , YAN Weiqing etc.

doi: 10.11729/syltlx20220141

[Abstract](96) [FullText HTML](31) [PDF 8262KB](13)

Abstract:
Since the temperature field conditions of the existing intake heating test device cannot meet the index requirements of a certain engine, the structural design, test scheme, temperature field evaluation method, and steady-state and transition state test scheme of the new intake heating device are carried out to ensure that the engine inlet temperature field meets the requirements. This paper makes a numerical simulation analysis of the temperature field uniformity using four engine inlet conditions and using the circumferential non-uniformity method. The simulation results show that the circumferential non-uniformity of the temperature field ≯1%. At the same time, the combined tests of a turbofan engine and the intake heating device under multiple operating conditions were carried out. The steady-state tests show that the circumferential non-uniformity of the temperature field at the highest engine speed was 0.4395%, and the temperature field distribution was consistent with the simulation results. The results of the transition state test show that the inlet temperature field unevenness is related to the engine inlet temperature change rate, and the inlet temperature regulation method is the key to meet the requirements of temperature field circumferential unevenness under different engine working conditions. The results of simulation analysis and joint test show that the newly designed inlet heating device can meet the requirements of circumferential unevenness of the inlet temperature field in the multi-condition engine test.

Aerodynamic pressure field reconstruction from sparse points using data assimilation method

HUANG Jun , GUO Yuxin etc.

doi: 10.11729/syltlx20230021

[Abstract](53) [FullText HTML](68) [PDF 7986KB](2)

Abstract:
In wind tunnel experiments, the high-precision pressure distribution of models is highly required, but existing measurement methods still have certain shortcomings. In order to obtain the global pressure distribution of the wind tunnel model, this paper assimilated the sparse measured data and numerical calculation data of the wind tunnel experiment by ensemble transform Kalman filter (ETKF), and realized the high-precision reconstruction of the full-space flow field based on the finite measurement points of the model surface. Two-dimensional airfoil RAE 2822 and NACA 0012 were used for experimental verification. Sparse reconstruction of pressure results of RAE 2822 is more consistent with the measured results than the linear theory correction. This effect is especially evident at the shock wave position, and the prediction error of the pressure coefficient is reduced by about 3%. The lift coefficient and moment coefficient of the wing calculated by using the modified ETKF set mean of attack angle and Mach number are less than 1% error from the experimental values. Experiment of NACA 0012 is oriented to the full-field sensing application of wind tunnel experiments and explore the feasibility of pressure reconstruction based on a small number of measurement points. The experimental results show that the relative error of pressure coefficients reconstructed using six measurement points on the wing object surface can be reduced to 2.42%, and the comparison results show that the assimilation effect is highly dependent on the data point locations.

Experimental study on the effect of rough surface on aerodynamic characteristics and flow field of low Reynolds number airfoil

DENG Haodong , XIA Tianyu etc.

doi: 10.11729/syltlx20230032

[Abstract](70) [FullText HTML](28) [PDF 17705KB](10)

Abstract:
In order to explore the influence of rough surfaces on aerodynamic characteristics and the flow field of the low Reynolds number airfoil and to deeply understand the action mechanism of rough surfaces, the SD8020 airfoil was used for experimental research (Re = 4 × 10⁴). The aerodynamic force of the airfoil was measured in the experiment, and the flow field around the airfoil was observed in detail by using luminescent oil-film, smoke wire flow visualization and hot wire technology. The results show that the lift coefficient of the smooth airfoil has nonlinear characteristics in the range of α = 0°～3°, and the abrupt change of the laminar flow separation bubble structure is the main reason for the nonlinear characteristics of the lift coefficient of the airfoil at low Reynolds number. Too small leading edge roughness (S_a⁺ = 0.00025) does not have significant influence on the flow field, but appropriate leading edge roughness (S_a⁺ = 0.0051, 0.013) can delay the separation of boundary layer, accelerate the reattachment of shear layer, and reduce or even eliminate laminar separation bubbles. So it can significantly reduce aerodynamic drag and increase the lift-drag ratio. The lift-drag ratio of the smooth airfoil is increased by 35.7% and 41.4%, respectively. When S_a⁺=0.013, the nonlinear characteristics of the lift coefficient growth is weakened at a small attack angle and the lift coefficient can increase significantly (e. g. the lift coefficient increases by 219.5% when α=2°). The roughness of the leading edge accelerates the growth of the disturbance (manifested as the growth of high-frequency velocity pulsation and T–S wave), rolls the vorticity of the wall into the flow field faster, and forms the vortex structure earlier. The vortex structure can strengthen the normal convection, improve the resistance of the boundary layer to the adverse pressure gradient, and delay the separation. After the boundary layer separation, the vortex structure plays a leading role in the transition process of the separated shear layer, speeding up the transition of flow to turbulence and flow reattachment in advance.

Comparative analysis between thin-film gauges and ALTP sensors in shock tunnel tests

CHEN Suyu , LIU Jichun etc.

doi: 10.11729/syltlx20220036

[Abstract](64) [FullText HTML](27) [PDF 6996KB](4)

Abstract:
In the shock tunnel tests, the main parameter to measure is the heat flux density, and the thin-film resistance gauges （TFRGs） are frequently used. As the uncertainty of the measured heat flux with TFRGs is relatively high resulting from the lack of direct validation method for TFRGs, the atomic layer thermopile （ALTP） heat-flux sensors are applied in shock tunnel tests for comparison with the TFRGs. ALTP sensors have a fast response time and a good linearity, and it can be used in a long duration to measure low heat flux density, which ensures that they can be easily calibrated with the high-accuracy light-based calibration device, so the transfer calibration method is established to on-line calibrate TFRGs in the shock tunnel tests. The experimental results confirm the stable measured heat flux with the ALTP sensors and the TFRGs in the different shock tunnel tests, and the difference between the two kinds of heat-flux sensors is less than 8%. Based on the discussion on the tracing chains of the transfer method for calibrating heat-flux sensors and the measured heat flux in tests, the comparison results show the potential that the ALTP heat-flux sensors can be used to on-line calibrate TFRGs in shock tunnel tests.

Experimental study on the effect of microscale flow on nanoparticle diffusion in polymer solutions

QU Hengchao , ZHENG Ping etc.

doi: 10.11729/syltlx20220048

[Abstract](50) [FullText HTML](26) [PDF 7846KB](2)

Abstract:
The diffusion of nanoparticles in physiological media is very important in the process of life evolution, information transmission, and drug delivery. Physiological media such as mucus, tissue fluid, and cytoplasm not only have complex porous properties, but also often exhibit microscale flows related to life activities. The interaction between flow and diffusion is extremely complex, and is affected by the porous properties of physiological media. In the experiment, the microfluidic technology is used to construct a microscale flow environment of polymer solution, the particle tracking technology is employed to measure the movement of nanoparticles, the movement characteristics of nanoparticles are then characterized based on statistical characteristics, and the effects of the microscale flow on nanoparticle diffusion are analyzed. The results show that the microscale flow has an effect on the diffusion of nanoparticles in the direction of the flow and the direction of vertical flow; the restricted degree of nanoparticle diffusion is weakened in the flow direction, showing the multi-stage characteristics of sub-diffusion, Brownian diffusion to super-diffusion; the diffusion of nanoparticles shows an approximate Brownian characteristic in the direction of vertical flow, but the diffusion coefficient is significantly higher than that of the static case. The analysis reveals that the effect of microscale flow on the nanoparticles diffusion in polymer solution is mainly due to the change of the polymer network structure and dynamics. The research results can provide a certain reference for the interpretation of the transport mechanism of nanoparticles in physiological media, and the design and transport enhancement of nano-drugs.

Experimental investigations on impingement dynamics and freezing behaviors of a supercooled water droplet onto a cold substrate

YANG Zaili , WANG Jingxin etc.

doi: 10.11729/syltlx20220051

[Abstract](60) [FullText HTML](29) [PDF 7922KB](5)

Abstract:
The impinging-freezing coupling process of millimeter-sized supercooled water droplets onto a cold substrate is experimentally investigated in this work. The effects of the droplet impact velocity, initial droplet temperature （−10 ℃ to 0 ℃）, and substrate temperature on the impingement dynamics and freezing behaviors of the droplet are comprehensively analyzed. The experimental results show that for a constant impact velocity, the maximum spreading diameter factor decreases with the initial droplet temperature, but it is independent of the substrate temperature. A modified universal model is proposed to describe the experimental results of the maximum spreading diameter factor. In addition, the nucleation time is advanced with the decrease of the substrate temperature, resulting in the increase of the final frozen area as the substrate temperature is −24 ℃ to −28 ℃, where ‘Coral’ nucleation appears in the contact line region during the retraction stage. Once the substrate temperature is lower than −28 ℃, ‘Fungus’ nucleation forms in thin liquid film during the spreading stage. Moreover, the freezing morphology is determined by retraction dynamics and solidification. The transition from the pancake to basin morphology is prompted due to the increase of the maximum spreading area.

Vehicle aerodynamic sensing technology based on surface distributed pressure

SUN Rong , LI Linkai etc.

doi: 10.11729/syltlx20230008

[Abstract](58) [FullText HTML](23) [PDF 10061KB](5)

Abstract:
In the environment of large crosswind or wind shear, the aircraft, high-speed rail, trucks, ships and other vehicles may rollover, which may cause safety accidents. For the crosswind or wind shear phenomenon, the existing technology mainly studies, monitors and gives early warning from the atmospheric macro environment, and often cannot accurately perceive the random aerodynamic load or sudden flow around the vehicle itself. We take the van truck as the research object, and propose a real-time sensing method of on-board aerodynamic force/moment based on the distributed pressure information on the surface. By measuring the distributed pressure on the body surface, the rolling moment coefficient of the characteristic section is obtained, so as to judge the rolling moment of the truck in the crosswind environment. The wind tunnel test results show that the rolling moment coefficient of the pressure tap section located at 0.15 L of the vehicle body is highly related to the rolling moment coefficient of the whole vehicle model, which can be used as a characteristic section to sense and judge its rolling moment, and we also use multiple section fitting to sense the rolling moment, which is more accurate than single section fitting, but needs to monitor the pressure at more positions of the body surface.

Applicability analysis of Sivells method in nozzle design with high Mach number and low total pressure

LI Zhenqian , SHI Yilei etc.

doi: 10.11729/syltlx20220045

[Abstract](124) [FullText HTML](48) [PDF 8203KB](26)

Abstract:
At present, the Sivells method is widely used for the design of the inviscid hypersonic axisymmetric nozzle contour. And then, the nozzle contour viscous correction is performed by solving the axisymmetric momentum equation. This design procedure is validated by nozzles in conventional hypersonic wind tunnels and shock wind tunnels, which are operated under high Mach number and high total pressure conditions. Meanwhile, there are few validation studies of this procedure under high Mach number and low total pressure conditions. In this study, the nozzle design procedure based on the Sivells method is used for Mach 6, 8, 10, and 12 nozzle contour design under the low total pressure condition. Furthermore, in order to analyze nozzle flowfields, numerical simulation and wind tunnel experiment are carried out. It can be found that, the flowfields in Mach 6 nozzle and Mach 8 nozzle are consistent with expectation and the jet flowfields are so good that are suitable for test. In contrast, there are some over-expanded areas in the flowfields of Mach 10 nozzle and Mach 12 nozzle, which results in higher Mach number than expectation in those areas. The jet flowfield quality of Mach 10 nozzle is better than that of Mach 12 nozzle. It can be concluded that, under the condition of low total pressure, the Sivells method still works well for Mach 6 nozzle and Mach 8 nozzle design. Meanwhile, the method is less effective when applied to the Mach 10 nozzle and Mach 12 nozzle design.

Experimental study and statistical analysis of flow field pulsation of spiked cylinder

WANG Yifan , QIN Qihao etc.

doi: 10.11729/syltlx20220078

[Abstract](124) [FullText HTML](42) [PDF 7875KB](10)

Abstract:
The cylinder with a pointed spike and the spiked cylinder with aerodome were investigated under the condition of Ma = 2.2 incoming flow using a direct-connected wind tunnel and a high-speed schlieren system. The experimental results were statistically analyzed to investigate the unsteady flow field pulsation of the spiked cylinder under supersonic incoming flow. Based on the transient data, the typical structure and evolution of the flow field were first interpreted. The convergence of the residuals was then used to assess the dependability of the statistical results. Finally, the pulsation characteristics of the flow field were further analyzed in terms of the time-averaged and pulsating flow fields. The results show that there is unsteady pulsation in the spiked cylinder flow field under the condition of the supersonic incoming flow, which is more intense in the case of the cylinder with a pointed spike and attenuated in the case of the spiked cylinder with aerodome, demonstrating the suppression of unsteady pulsation in the flow field by the aerodome.

Infrared thermogram measurement experiment of hypersonic boundary-layer transition of a lifting body

CHEN Jiufen , XU Yang etc.

doi: 10.11729/syltlx20220030

[Abstract](138) [FullText HTML](77) [PDF 8806KB](33)

Abstract:
For a lifting body model, the boundary layer transition infrared thermogram measurement experiment was carried out in the conventional hypersonic wind tunnel, and the influence of different unit Reynolds number and Mach number on the lifting body boundary layer transition was studied, which was compared with the calculation results of the e^N method. The length of the experimental model is 800 mm, the unit Reynolds number is 0.46×10⁷～3.94×10⁷ m^–1, the Mach number is 5～8, and the angle of attack is 0°. The transition position and transition front of the boundary layer on the surface of the model are obtained by the large-area infrared thermogram technology. The analysis of the experimental results shows that there are crossflow instability and the second mode transition in the boundary layer of the lifting body. As the unit Reynolds number increases, the crossflow transition effect increases, the temperature rise on the lower and upper surfaces of the model increases, the transition front moves forward, and the transition area expands; as the Mach number increases, the crossflow transition effect gradually weakens and the transition position moves downstream, and the transition area significantly shrinks back. Moreover, the transition N factor at different Mach numbers and unit Reynolds numbers are relatively close, but the N factors of the upper and lower surfaces are different. The lower surface is about 6, and the upper surface is about 2.5. The high-frequency second mode transition occurs in the side edge at high unit Reynolds numbers.

Pressure sensitive paint measurement correction method based on surface spline interpolation

JING Zhiwei , WANG Libo etc.

doi: 10.11729/syltlx20220027

[Abstract](100) [FullText HTML](62) [PDF 6692KB](4)

Abstract:
The PSP（Pressure Sensitive Paint） measurements correction after the wind tunnel test is often implemented through the least square method, and it tends to neglect the chordwise and spanwise flow characteristics on the wing. By employing the IPS （Infinite Plate Spline） technique, a hybrid correction method and process for the PSP test results was presented. A full-span airplane model, with PSI （Pressure Scanner Instrument） and PSP on the upper and lower surfaces of the wing, was utilized to carry out the PSP test and PSI test simultaneously in a transonic wind tunnel with the 2.4 m test section. The pressure measurements were conducted at Ma = 0.735 and in the angle of attack range from −6.38° to 10.59°. Test results indicate that the PSP data demonstrate a good agreement with PSI data. However, the PSP test system with only one camera shows a poor capacity to capture the aerodynamic field at the wing leading edge. The hybrid correction method for PSP results has proven to an effective approach, and the corrected data reveal that the hybrid correction can better deal with the pressure distribution characteristics of the full wing.

Experimental study on RP3 aviation kerosene oblique detonation engine

HAN Xin , ZHANG Wenshuo etc.

doi: 10.11729/syltlx20220090

[Abstract](1330) [FullText HTML](310) [PDF 9313KB](55)

Abstract:
The oblique detonation engine has great potential application in high flight Mach number airbreathing vehicles because of its higher thermodynamic efficiency and smaller size. The research about the oblique detonation engine is renewed all over the world in recent years. However, all of the oblique detonation experiments are conducted with hydrogen fuel or ethylene. There is no experimental result about the kerosene oblique detonation. In order to examine the application feasibility of kerosene oblique detonation engine, the experimental study on the liquid RP3 aviation kerosene oblique detonation engine is conducted in JF-12 shock tunnel and the test time is about 50ms. The difficult issue for the initiation of kerosene oblique detonation is that the ignition delay time of kerosene-air is too long and the autoignition cannot occur in the combustor. A new forced detonation initiation method is put forth to deal with this key issue. The total temperature of JF-12 shock tunnel is 3800 K and the global equivalence ratio is 0.9, which replicates Mach 9 flight-equivalent condition. The steady-state oblique detonation is obtained successfully during the experiments, which demonstrates the application feasibility of the kerosene oblique detonation engine.

Pressure fluctuation experiments of hypersonic boundary-layer on a 7-degree half-angle sharp cone

CHEN Jiufen , XU Yang etc.

doi: 10.11729/syltlx20210054

[Abstract](136) [FullText HTML](53) [PDF 11507KB](20)

Abstract:
In a conventional hypersonic wind-tunnel, pressure fluctuations of the boundary layer on a 7-degree half-angle sharp cone are measured by surface sensors and are analyzed by the linear stability theory. The influences of unit Reynolds numbers and Mach number on the stability and transition position of the boundary layer are studied. The length of the test model is 800 mm and the radius of the head is 0.05 mm. Test unit Reynolds numbers range from 0.49×10 ⁷m^–1 to 2.45×10⁷ m^–1. Test Mach numbers range from 5 to 8. The angle of attack is 0°. The transition position and the energy spectrum distribution of the disturbance wave in the boundary layer are obtained by the quantitative infrared thermography and high frequency surface pressure fluctuation measurement techniques. The frequency and growth rate of the most unstable wave are analyzed by using the linear stability theory. The experimental results show that the fluctuating pressure signal with obvious characteristics of the unstable wave spectrum can be measured in the transition region. The frequency of the pressure fluctuation is close to that of the second mode instability analyzed by the linear stability theory, and the amplitude variation trend is also similar to that of the theoretical analysis. With the increase of the unit Reynolds number, the instability appears earlier, the dominant frequency is increased, and the transition onset moves forward. The unstable wave in the boundary layer contains the first and second modes. When the free-stream Mach number is equal to 5, the transition is caused by the first mode, and when the Mach number is above 6, the transition is attributed to the second mode.

Experimental research on the influence of turbulence intensity on boundary layer transition in Mach 3 supersonic flow

LI Meng , ZHAO Huiyong etc.

doi: 10.11729/syltlx20220087

[Abstract](119) [FullText HTML](45) [PDF 9099KB](20)

Abstract:
There is still a shortage of the experimental research of boundary layer transition in compressible flows nowadays due to the difficulty in measuring the turbulence intensity. Aiming at studying the influence of the turbulence intensity on supersonic boundary layer transition, a plate model is tested in a blow-down facility （FL-24y of CARDC） at Mach 3. The turbulence intensity of the flow is changed by adjusting the arrangements in the stabilization section of the wind tunnel, which covers a range from 0.82% to 1.63%. The turbulence intensity is measured by interferometric Rayleigh scattering, while the boundary layer transition is derived by infrared thermography. The CFD simulation of the plate model transition is conducted based on the γ-Re_θ transition model. The results show that the transition onset position （F_onset） and transition end position （F_length） obtained by the experiment and the simulation agree well, with the maximum relative error coefficient of 2% in F_onset and of 5% in F_length, which provides support to gain a deeper insight into the boundary layer transition mechanism in supersonic flows.

Study on evaporation heat transfer characteristics of sessile droplets based on temperature measurement of double layer temperature sensitive paint

LI Bingjie , ZHANG Shulei etc.

doi: 10.11729/syltlx20220132

[Abstract](87) [FullText HTML](46) [PDF 6787KB](11)

Abstract:
As a new non-contact temperature measurement method, temperature sensitive paint has the advantages of low cost and fast response. In this paper, a temperature measurement technology based on double layer temperature sensitive paint was used to study the heat transfer characteristics of sessile droplet evaporation. The temperature distributions at the contact surface between the droplet and the heating substrate and at the back of the substrate were obtained by measuring the temperature with a double-layer temperature sensitive paint. A one-dimensional unsteady inverse heat conduction model was established to obtain the heat flux distribution at the interface between the droplet and the heating substrate. The results show that the droplet vaporization process can be divided into three stages: initial heating stage, convection unit evaporation stage and film evaporation stage. In the initial heating stage, the heat flux increases rapidly. In the convection unit evaporation stage, the heat flux decreases gradually and remains basically unchanged. In the film evaporation stage, the heat flux first increases, and then decreases rapidly as the droplet almost completely evaporates. The reliability of the experimental method is verified by checking the heat quantity of droplet evaporation. The research results in this paper are helpful to broaden the experimental measurement method of heat flux during phase change heat transfer.

Visualization experiment of wave dynamics in pressure oscillation tube

GUO Jiangtao , ZHOU Yihui etc.

doi: 10.11729/syltlx20220039

[Abstract](60) [FullText HTML](32) [PDF 18534KB](4)

Abstract:
Gas Wave Refrigerator（GWR） is a kind of equipment with strong adaptability to complex working conditions. It has the advantages of high refrigeration efficiency, and can work with liquid. The pressure oscillation tube is the core part of GWR. A visual flow field measurement platform was designed to study the wave motion inside the pressure oscillation tube. The flow field splices and the schlieren technique are used to obtain the density gradient field in the tube, and the results are compared with the theoretical calculation of the two-dimensional Euler equation. The deviation between the experiment and the simulation is 3.2%. Based on the above method, experiments with different pressure ratios and rotational speeds were carried out. The experimental results show that the shock Mach number can be increased by increasing the pressure ratio or speed. When the pressure ratio increases from 1.5 to 3.0, the intensity of the shock wave and expansion wave increases significantly. When the rotational speed increases from 800 r/min to 2400 r/min, the motion path of the expansion wave system gradually bends towards the nozzle, which prolongs the time of the expansion wave at the nozzle.

Droplet spreading on an oblique surface

LU Jie , LI Yalei etc.

doi: 10.11729/syltlx20220012

[Abstract](256) [FullText HTML](87) [PDF 7340KB](19)

Abstract:
Droplet spreading on a surface is ubiquitous in a variety of applications including aerospace, industry, and agriculture. Majority of these impacts are oblique, while previous studies focused on orthogonal impacts. Oblique impacts cannot be understood directly by previous theories and/or models. Evolution of film formation following a droplet impacting an oblique surface is investigated experimentally. Evolution of the film shape is obtained under various inclination angles and Weber numbers. Based on a new theory of droplet spreading on oblique surfaces, evolution of the film shape is analyzed. It is found that the film shape at small inclination angles can be predicted reasonably, but the error between the predicted maximum lamella width along the inclination direction and the experimental data is relatively big at large inclination angles since the length of the upstream lamella is assumed as a constant in the theory. Modifications of the theory including more detailed analysis of the length of the upstream lamella lead to an analytical model which permits the theoretical determination of the maximum lamella shape. It is shown that the error between the predicted results and the experimental results can be reduced from 61.8% by the previous theory to 3.2%. The model provides a better prediction on the lamella shape at large inclination angles, and a more concise and accurate theoretical tool for engineering applications.

Wind tunnel test technique of continuous varying Mach number for air-breathing vehicle

ZHOU Jian , ZHANG Jiang etc.

doi: 10.11729/syltlx20210189

[Abstract](180) [FullText HTML](50) [PDF 9642KB](7)

Abstract:
To study the start/unstart phenomenon of the air-breathing vehicle inlet caused by acceleration or deceleration, which also bring the problem of aerodynamic mutation on vehicle, the test technique of continuous varying Mach number was performed in the 1.2 m supersonic wind tunnel based on the flow mechanism of the 2D wedge shock wave. By developing the shock wave generator system, continuous varying Mach number was realized successfully in one wind tunnel test process. And it has also been confirmed that the technical method can make Mach number vary simply and quickly with high quality and precision. Through the flow-field calibration, the quality of the instantaneous flow-field in variable Mach number region meets the standards of GJB eligibly, and thus the field can be used for force and pressure test compliantly. In addition, the test of inlet starting characteristics was carried out and the dynamic process and critical state from start to unstart were captured, which indicates that the test results agree with the numerical simulation accurately. The test technique could provide effective support for supersonic air-breathing vehicle in aerodynamic performance prediction and study.

Evolution of high-speed cavity flow based on PIV technology

WU Jifei , ZHOU Fangqi etc.

doi: 10.11729/syltlx20210144

[Abstract](108) [FullText HTML](63) [PDF 8883KB](8)

Abstract:
In cavity structure, complex flows and high-intensity noises appear under the high-speed condition, seriously affecting the aerodynamic characteristics and structural safety of the aircraft. Through the methods of the PIV technology and dynamic pressure measurement, the cavity with a length-depth ratio of 3 to 10 is experimentally investigated in the range of Mach number 0.4 to 0.8. The influences of the length-depth ratio and Mach number on the flow field structure in the cavity are emphatically analyzed, and the correlations between the noise intensity and the flow velocity are revealed. The results show that: as the length-depth ratio increases, the thickness of the shear layer in the cavity increases rapidly and expands into the cavity, leading the impact position on the cavity to move down from the back wall to the bottom, and causing the flow type in the cavity to change from open to closed. The increase of the Mach number inhibits the shear layer from expanding into the cavity and induces the main recirculation vortex to move back and the flow type to be open. The amplitude of the overall sound pressure level is positively correlated with the flow velocity in the back of the cavity.

Calibration results and analysis of thin-film gauges calibrated with the transfer method

YANG Kai , LIU Jichun etc.

doi: 10.11729/syltlx20210129

[Abstract](154) [FullText HTML](43) [PDF 6370KB](6)

Abstract:
Considering the fact that there are more error sources in the measured heat flux with thin-film gauges when the two-stage approach is applied to determine the thermal product and resistance-temperature factor, the transfer method is applied to directly calibrate thin-film gauges, in which the thermal product and resistance-temperature factor are treated as the sensitivity coefficients. To get the consistent calibration results of different thin-film gauges fabricated in a batch, the sensitivity coefficients are divided by the resistance-temperature factors of the thin-film gauges, and then the correction sensitivity coefficients are consistent. With the transfer calibration technique, the calibration results of thin-film gauges show a good linearity with a relative expanded uncertainty below 6.5%, which is lower than that reported in other researches, in which the two-stage approach is used to calibrate thin-film gauges.

Experimental study on Rayleigh–Bénard convection during supercritical phase transition of carbon dioxide

ZHAO Yifan , WU Di etc.

doi: 10.11729/syltlx20230003

[Abstract](79) [FullText HTML](33) [PDF 10764KB](16)

Abstract:
Supercritical fluid is a kind of special fluid under extreme conditions (temperature and pressure are above the critical point). The Rayleigh-Benard (RB) convection of supercritical fluid driven by buoyancy is a new nonlinear thermal convection system. Its buoyancy does not conform to the Boussinesq approximation. Under the action of temperature difference, the physical properties of RB fluid show severe distortion near the critical point, accompanied by abundant flow and phase transition coupling processes. In this experiment, a transparent sapphire pressure vessel capable of carrying supercritical carbon dioxide (SCO₂) was designed to establish RB convection of supercritical fluid under the effect of vertical temperature gradient. The flow structure and supercritical phase transition process under different temperature differences were observed. The velocity field of "atomized" droplets was calculated by image cross-correlation algorithm. In the experiment, platinum resistance temperature measurement was used to accurately control the temperature of the upper and lower ends of the container, and the evolution of various flow modes and velocity fields in the linear cooling process was studied. In the linear cooling process, SCO₂ goes through three typical processes: supercritical flow, transcritical flow and gas liquid two-phase flow. The strong coupling of the transcritical phase transition with buoyancy convection results in the heterogeneous unsteady flow of supercritical carbon dioxide RB convection. It shows that the supercritical RB convection is extremely sensitive to temperature difference, and the larger the temperature difference is, the more intense the convection in the supercritical domain is. With the decrease of temperature, the atomized droplets condense to form abundant structure of multi-layer flows, which finally turn to the two-phase flow.

Measurement investigation of rotational temperature and vibrational temperature in hypersonic wind tunnel rarefied flow field

CHEN Aiguo , TIAN Ying etc.

doi: 10.11729/syltlx20210192

[Abstract](49) [FullText HTML](51) [PDF 7297KB](6)

Abstract:
The inconsistency of rotational temperature and vibrational temperature in the rarefied flow field is a concrete manifestation of thermodynamic non-equilibrium. The non-intrusive measurement method of rotational temperature and vibrational temperature in the rarefied flow field can be measured by the Electron Beam Fluorescence (EBF) technique. The basic principle and measurement method of EBF were introduced in this paper. Experiment was carried out in the M12 and M16 conical nozzle of the Φ0.3m hypersonic low density wind tunnel. The rotational temperature maximum relative uncertainty is 0.26% and the vibrational temperature maximum relative uncertainty is 0.8% from the analysis of repetitive measurement results. The distribution of rotational temperature and vibrational temperature on the exit section of the M12 and M16 conical nozzle reflects the characteristics of expansion flow of the conical nozzle. The measurement results of three states of each nozzle show that with the increase of rareness, the larger the deviation between the vibrational temperature and the rotational temperature is, the more prominent the thermodynamic non-equilibrium phenomenon appears.

Research progress of improving nanofluid fuel performance

GAO Yi , XU Xingxing etc.

doi: 10.11729/syltlx20220119

[Abstract](68) [FullText HTML](34) [PDF 7312KB](7)

Abstract:
Nanofluid fuel is a kind of suspension liquid, which is made by adding nanoparticles into the liquid fuel. It has advantages of high energy density and shorter ignition delay, and thus shows the potential of improving the burning characteristics of the fuels. To further improve the performance of nanofluid fuels and explore more effective performance control methods, the progress of research on nanofluid fuels in recent years at home and abroad is briefly reviewed in this work. Researches on the improvement of the stability performance, rheological performance, evaporation performance, ignition performance and combustion performance of nanofluid fuels are introduced, and the corresponding tailoring methods and mechanisms are analyzed. Adding surfactant and surface coating are effective methods to improve the stability of nanoparticles in the fuel. The methods of regulating ignition and combustion performance are based on improving the heat conduction and absorption capacity of droplets and promoting the heat release of metal particles, which mainly include nano-metal particles, nano-metal oxides, and new metastable intermixed composites. The existing problems in current research are summarized. More importantly, it is pointed out that the future study of nanofluid fuels should focus on broadening the boundary of the fuel, exploring new surfactants, and establishing the theoretical framework of ignition and combustion.

Multi-objective optimization method for light-field multi-spectral pyrometer

SUN Linlin , FANG Hua etc.

doi: 10.11729/syltlx20230011

[Abstract](141) [FullText HTML](53) [PDF 5429KB](16)

Abstract:
A light-field multi-spectral pyrometer is designed for two-dimensional, high-temperature measurements. The proposed method is based on an unfocused light-field camera, which can simultaneously record directions and intensities of incident rays. The direction information of rays is substituted by radiation spectrums via placing an array of filters in front of the camera’s main lens, such that the image sensor can simultaneously acquire spectra and intensities of rays. For multi-spectral data processing, how to obtain the accurate target temperature under unknown spectral emissivity is a difficult problem to be solved. A multi-objective optimization method is proposed to obtain the inverse true temperature and spectral emissivity without assuming the emissivity model. In this method, the multi-objective function is established according to the radiation equations. The emissivity constraint conditions are set for the objective function, and the penalty function method is used to solve the optimization problem. The calibration experiment results of the black-body furnace show that the relative error of the light-field multi-spectral pyrometer method is less than 1%, which proves the feasibility and reliability of the proposed design and temperature inversion method.

Two-dimensional distribution measurement of direct-connect scramjet combustion flow field based on TDLAS multi-absorption lines

XIA Huihui , ZHANG Shunping etc.

doi: 10.11729/syltlx20220103

[Abstract](73) [FullText HTML](34) [PDF 6180KB](9)

Abstract:
Aiming at the demand of two-dimensional distribution high-resolution measurement of temperature and water vapor concentration in non-uniform scramjet combustion chamber expansion section, advanced tunable diode laser absorption spectroscopy (TDLAS) reconstruction method has been developed. By increasing the number of water vapor absorption lines obtained by scanning the laser wavelength, the number of equations for solving the reconstruction problem correspondingly increased, combining the absorbance equations of all absorption spectra under all laser paths, constructing the optimization objective function with temperature and concentration as unknowns, and using the global optimization simulated annealing algorithm to reconstruct the temperature and water vapor concentration distribution. In the direct-connect scramjet combustion test, the orthogonal optical path layout is adopted, and the square optical mechanical structure with 16 measuring optical paths of 5 horizontal and 11 vertical channels is designed. TDLAS measurement system is assembled, and the time division multiplexed direct absorption detection method is adopted for 5 DFB lasers, with the measurement frequency of 4 kHz. Five water vapor absorption spectral lines (7467.77、7444.36、7185.60、7179.75 and 6807.83 cm) can be obtained at each measured optical path, the system has carried out thermometric validation by using high-temperature furnace on the laboratory, and the temperature measurement deviation is within 2.7%. In the test, the absorption spectrum data synchronously collected under 16 optical paths are processed offline, and the distribution data of temperature field and water vapor partial pressure under various states of ignition, combustion and flameout are obtained. The test results show that TDLAS multi-absorption measurement technology can realize accurate and stable reconstruction, and meet the engineering application requirements of complex combustion flow field diagnosis and bad working conditions.

Experimental study on flow characteristics of pitching hydrofoil via stereo shadowgraph

WEI Jinwu , MEI Xiaohan etc.

doi: 10.11729/syltlx20220095

[Abstract](123) [FullText HTML](50) [PDF 8306KB](7)

Abstract:
In order to study the jet flow characteristics caused by the pitching hydrofoil, a three-dimensional shadow imaging system is utilized to measure the turbulent flow field. By comparing the results of particle image velocimetry, two-dimensional particle tracking velocimetry and three-dimensional particle tracking velocimetry, it is found that the pure pitch motion of the rigid symmetric NACA0012 airfoil at a fixed position in the static fluid would produce weak jets in two directions, accompanied by the generation of small-scale vortices. The results of velocity statistics show that when the amplitude of the hydrofoil rational angle is large, more obvious vortex structure and velocity change are produced. The study obtained the three-dimensional wake structure generated by the pitching hydrofoil movement, and found that there is also a symmetric vortex structure in the depth direction. The results show that the velocity component in the depth direction generated by the pitching hydrofoil movement can not be ignored under the limited airfoil aspect ratio.

Study on electric and thermal characteristics of CO₂ arc heater

OU Dongbin , YANG Guoming etc.

doi: 10.11729/syltlx20220065

[Abstract](78) [FullText HTML](50) [PDF 7131KB](4)

Abstract:
On the 300 kW DC axial tube electrode arc heater, the U–I characteristics and thermal efficiency of CO₂ and air are measured by experiment, and the regression analysis is carried out by using the similarity criterion number. The unified relationship of electric and thermal characteristics that can be applied to the two media is obtained, and compared with similar heaters abroad. The results show that CO₂ and air arc heaters have similar electric and thermal characteristics, under the same input parameters (arc current and gas flow); the total pressure of CO₂ is 18% lower than that of air, but the arc voltage, enthalpy and thermal efficiency are 5.9%, 6.7% and 10.9% higher respectively; the regression errors of U–I characteristics and thermal efficiency are −13.0%～11.4% and −33.0%～34.7% respectively. This relationship plays an important guiding role in the operation and commissioning of the high-power arc heater.

Influence and regulation of magnetic field on wettability of ferrofluid droplet on hydrophobic surface

OUYANG Yi , WEN Mingfu etc.

doi: 10.11729/syltlx20220086

[Abstract](164) [FullText HTML](64) [PDF 7437KB](24)

Abstract:
The controllable dynamic behavior of ferrofluid droplets under the magnetic field can be used to realize directional transport of small droplets or bubbles in microfluidic devices, anti-icing, droplet condensation, mineral flotation and other fields. At present, the mechanism, influencing factors and regulation methods of the field-assisted wetting behavior of magnetic fluid on the superhydrophobic surface are not clear. The wetting behavior and droplet shape evolutions of water-based ferrofluid on a hydrophobic surface under an external magnetic field are studied experimentally. Under the vertical magnetic field, the effects of the magnetic induction intensity and ferrofluid droplet size on the droplet wetting behaviors are investigated, and the contact line diameter and contact angle of the droplet are measured experimentally. The experimental results show that the apparent contact angle of the ferrofluid droplets decreases from above 90° to below 90° under the action of the weak magnetic field. Under the magnetic field, the nanomagnetic particles in the magnetic fluid form a chain structure along the direction of the magnetic field line and the droplet contact angle changes. Through a scaling analysis, the theoretical relationship of the magnetic field and the contact angle is established and it successfully predicts our experimental results. The work is valuable for controlling the wetting properties of the ferrofluid droplets on the solid surfaces under the magnetic field.

A brief review on trans/supercritical internal flow and jet

JIANG Guanyu , WEN Haocheng etc.

doi: 10.11729/syltlx20220083

[Abstract](162) [FullText HTML](77) [PDF 7495KB](19)

Abstract:
Aviation kerosene is expected to act as the primary coolant of advanced gas turbine engines. In such situations, the aviation kerosene would exist at subcritical conditions near the critical point or even at supercritical conditions. Correspondingly, it is of vital importance to study the nozzle internal flow and jet for the design of engine combustors. This paper focuses on the internal flow characteristics and jet characteristics under trans/supercritical conditions. The review shows that the existing researches of the trans/supercritical internal flow are mainly limited to small-molecular or simple fluids, constant cross-section pipes, and narrow conditional parameters. The location of phase change depends on thermodynamic characteristics, geometric configurations, and injection parameters. The mixing efficiency of the trans/supercritical jet is largely affected by thermodynamic characteristics. However, the research on trans/supercritical internal flow characteristics of hydrocarbon fuel inside constriction nozzle channels and jet characteristics based on relatively complex nozzle configurations remains to be further developed. Accurate thermodynamic models of supercritical aviation kerosene remain to be established. The deformation and breaking mechanism of the jet fluid interface as well as the jet mixing behavior remains to be captured through advanced optical diagnostic methods. The mixing characteristic parameters and their change laws remain to be summarized and described.

1.2 m large-field focusing schlieren technique

XIE Aimin , XING Yanchang etc.

doi: 10.11729/syltlx20220047

[Abstract](148) [FullText HTML](103) [PDF 7524KB](24)

Abstract:
In the conventional “Z” structure schlieren technique, due to the limitation of large-size optical element materials and processing technology, the size of the test field is usually less than 1 meter. In order to show the flow field of a large-scale model in a wind tunnel, the focusing schlieren technique is proposed to show the flow field in the 1.2 m test area. According to the imaging principle, the large size Fresnel lens are replaced by a matrix light source. After solving the key technologies such as the engineering design of large-size light source splicing, the development of large-diameter focusing lens and the production of high-definition imaging screen, two sets of focusing schlieren systems with the test field of view of 1.2 m × 1.2 m were established, and the schlieren images of the hypervelocity flow field with high sensitivity were obtained in the wind tunnel. The flow visualization with larger field is expected to be realized through the splicing of larger size light sources.

Research on flow characteristics of underwater passive fluidic thrust vectoring nozzle

FENG Chao , GU Yunsong etc.

doi: 10.11729/syltlx20220071

[Abstract](112) [FullText HTML](75) [PDF 10196KB](10)

Abstract:
We designed an underwater passive fluidic thrust vectoring nozzle. It can easily generate pressure difference on both sides of the primary jet to deflect the jet only by controlling the valves of the secondary flow channel. However, the nonlinear features in the control law of the thrust vectoring angle such as “sudden jump” and “hysteresis” limit the further application of this technology. In this research, the flow characteristics of the primary jet in different transverse sections of the nozzle were studied by the dye flow visualization technology and particle image velocimetry technology. We discovered flow structures such as shear layer vortices, trailing edge backflow, and separation bubbles. Three-dimensional flow structures were also observed, including the transverse flow in the near-wall region and the corner flow at the joint of two walls. The study of the interaction law between flow structures provides a physical model basis for solving the nonlinear problems such as jump and hysteresis of the thrust vectoring control law.

Roll-yaw control of flying wing aircraft at a high angle of attack based on jet control

GE Zengran , SHI Zhiwei etc.

doi: 10.11729/syltlx20220104

[Abstract](107) [FullText HTML](47) [PDF 7105KB](12)

Abstract:
The complex flow field structure and the interaction between vortex structures make the flying wing configuration aircraft prone to transverse uncommanded motion at a high angle of attack. To suppress the uncommanded motion, two sets of jet actuators are arranged on the vehicle using two existing active jet control techniques, the control effect of the actuators is verified through wind tunnel force measurement experiments, and the mutual coupling relationship between the two sets of jet actuators is clarified. A virtual flight experiment is conducted in the wind tunnel to capture the uncommanded motion of the flying wing configuration aircraft in the transverse direction, and two methods, PID and deep reinforcement learning, are applied to suppress the uncommanded motion in this kind of highly coupled and nonlinear problem. The wind tunnel experiments show that the deep reinforcement learning method is more effective in controlling the highly coupled and nonlinear problem, and the trained intelligent model can effectively suppress the transverse uncommanded motion of the flying wing configuration aircraft model.

Experimental study on characteristic calibration of separated exhaust system

LI Qiufeng , LI Mi etc.

doi: 10.11729/syltlx20220056

[Abstract](98) [FullText HTML](45) [PDF 8779KB](5)

Abstract:
In flight testing, the aeroengine flight thrust is indirectly obtained by the gas generator method. In order to improve the calculation accuracy of the flight thrust, it is necessary to accurately obtain the characteristics of the exhaust system. The laboratory calibration test and numerical simulation research were carried out by using the large bypass ratio separated exhaust system scale model. The results show that: the core nozzle characteristics obtained by the two methods are consistent, and the values are close. When the maximum core nozzle pressure ratio is 1.44, the deviations of the mass flow and the thrust are 0.73% and 0.18%, respectively; the characteristics of the separated exhaust system obtained by the two methods have the same trend and close values. When the max bypass nozzle pressure ratio equals 1.46, the deviations of the mass flow and the thrust are 0.64% and 0.18%, respectively; when the physical model and geometric model of the large bypass ratio separated exhaust system are reasonably simplified, the characteristic deviations of the separated exhaust system obtained by the two methods are in good agreement.

Research on the double-inlet test method in low speed wind tunnel

TANG Jianping , SHANG Yinhui etc.

doi: 10.11729/syltlx20220059

[Abstract](129) [FullText HTML](56) [PDF 13166KB](8)

Abstract:
In order to meet the requirement of the double-inlet test in the 4 m magnitude low speed wind tunnel, a test method of the double-inlet test in the 4 m × 3 m low speed wind tunnel of LSAI of CARDC was proposed. According to the method, a model is supported by one pole, and each inlet mass flow is simulated and controlled by an ejector with a digital pressure regulating valves system. In this method, the range of AOA is −10°～90°, the range of AOS is −45°～45°, the simulating maximum of the double-inlet mass flow is 2.9 kg/s and 1.4 kg/s. To validate the method, a double-inlet test was completed in the low speed wind tunnel. The test results show: the model is less affected by pipeline aerodynamics. The independent model and ejector support mechanism meets various model support requirements. Double inlets mass flow simulation and control are completely independent, which meets the requirement of studying interactions for double inlets.

Experimental investigation on anti-icing mechanism and characteristics of superhydrophobic electrothermal coupled surface

LIU Xinle , LI Wenfeng etc.

doi: 10.11729/syltlx20220062

[Abstract](210) [FullText HTML](94) [PDF 9559KB](9)

Abstract:
As a novel anti-icing technology, superhydrophobic electrothermal coupled surface anti-icing possesses an excel-lent anti-icing efficiency with low energy consumption. Based on the water droplet impact behaviors and the wetting characteristics of the superhydrophobic surface, a prediction model of the heat flow density of superhydrophobic electrothermal coupled surface anti-icing is developed according to the thermal balance theory of the icing surface. The experimental analysis of the superhydrophobic electrothermal coupled surface anti-icing is carried out in a low-speed icing wind tunnel. The results show that the difference between the theoretical anti-icing heat flux and the experimental results is less than 6%, which verifies the prediction model. The analysis of the experimental results and energy consumption shows that the superhydrophobic electrothermal coupled surface anti-icing effectively reduces the energy consumption compared with the electrothermal method. With the freestream velocity of 10 m/s, liquid water content of 1 g/m³, mean volume diameter of 65 μm, and temperature of −15 ℃, the superhydrophobic coating can effectively prevent the formation of backwater due to its wetting property. For dry and wet surface anti-icing, the superhydrophobic electrothermal coupled surface anti-icing method reduces the energy consumption by about 43% and 33% respectively compared with the electrothermal method.

PLIF investigation on effects of chamber aspect ratio on flow and mixing in cross-shaped mixers

YANG Huan , ZHANG Wei etc.

doi: 10.11729/syltlx20220038

[Abstract](133) [FullText HTML](42) [PDF 7176KB](9)

Abstract:
Planar Laser-induced Fluorescence （PLIF） was used to study flow and mixing characteristics in cross-shaped mixers with four chamber aspect ratios r（r=0.5, 1.0, 1.5 and 2.0） at 10<Re<500. Results show that, there are four flow regimes in the mixers with different depths, including the segregated flow, steady engulfment flow, pulsation flow and unsteady engulfment flow. For the steady engulfment flow, the flow field is dominated by three co-rotating vortices for r<1.0, but the center and satellite vortices rotate in opposite directions for r≥1.0. For the pulsation flow, the center vortex shrinks and expands periodically, and the fluid oscillates throughout the chamber for r>1.0. For r=1.0 and 0.5, the shedding of vortex rings emerges downstream. For the unsteady engulfment flow, periodical vortex merging and breakup is observed for r=1.0. For r=0.5, vortex breakup is invisible, and instead, the center vortex merges with a satellite vortex periodically. For r>1.0, the center vortex experiences growth, deformation, and breakup processes. Mixing in cross-shaped mixers was evaluated by the time-averaged intensity of segregation （IOS）, and the mixing mechanism is revealed. An increase in chamber aspect ratios decreases the critical Reynolds number for the engulfment flow and pulsation flow, which causes the mixing enhancement in the chamber at low Re.

Ice cloud parameter identification method in icing wind tunnel based on multimodal fusion

XIE Teng , XIONG Hao etc.

doi: 10.11729/syltlx20220077

[Abstract](122) [FullText HTML](76) [PDF 7957KB](13)

Abstract:
The cloud field calibration of icing wind tunnels usually has the disadvantage of high instrument dependence. To solve this problem, this paper proposes a method for identifying the parameters of cloud fields in icing wind tunnels based on multi-modal fusion. This method takes the icing image of the test model together with the parameters such as the angle of attack, air velocity, air temperature, and icing duration of the model as input, extracts and fuses the two characteristic parameters, and takes the liquid water content （LWC） and the average volume diameter of water droplets （MVD） as the output to train the neural network model. And then the rapid identification of icing cloud parameters is realized. In order to verify the effectiveness and feasibility of the proposed method, the paper takes NACA0012 airfoil icing as the research object, develops the cloud field identification program of the icing wind tunnel, analyzes the influence of the fusion proportion, and obtains the best network model suitable for ice parameter identification. On this basis, simulation and experimental evaluation are carried out. The full scale error of the proposed method for LWC and MVD is less than 12%, which has high identification accuracy and good generalization performance, and can provide an important supplement for the identification of cloud fields in the icing wind tunnel.

Experiment of aerodynamic performance of axial compressor at low Reynolds number condition

LEI Pengfei , ZHOU Enmin etc.

doi: 10.11729/syltlx20220026

[Abstract](136) [FullText HTML](66) [PDF 6746KB](10)

Abstract:
Aerodynamic performances of the axial compressor of the 0.6 m continuous transonic wind tunnel are tested under various pressure conditions, and the Reynolds number effects are studied experimentally. The lowest total pressure of the compressor inlet is about 3 kPa, and the corresponding Reynolds number is approximately 5×10⁴. Test results show that the Reynolds number effects are significant when as Reynolds number is below the critical value, which is 5×10⁵ in the compressor design. Compared to the large Reynolds number condition, the pressure ratio under the low Reynolds number condition reduces rapidly, while the surge margin changes slightly. The mechanical loss of the shaft becomes the major loss of the compressor as the operation pressure drops, and has a significant influence on the compressor efficiency. Additionally, the correlations of the pressure ratio and efficiency with Reynolds number, obtained by data analysis, can offer a useful reference for design and numerical simulation of the axial compressor under the at low Reynolds number condition.

Crossing shock waves/transitional boundary layers interactions in the double vertical wedges configuration

YI Miaorong , ZHANG Ruoling etc.

doi: 10.11729/syltlx20220050

[Abstract](185) [FullText HTML](97) [PDF 7850KB](17)

Abstract:
Study on crossing shock waves/transitional boundary layer interaction in the double vertical wedges configuration was carried out using wind tunnel tests and numerical calculations. The wind tunnel tests were carried out at Φ 600 mm pulse combustion wind tunnel. The Mach number of the free stream condition is 3.0, and the unit Reynolds number is 2.1×10⁶ m⁻¹. The schlieren images, wall pressure and wall heat fluxes were obtained during the tests. The results show that because of the adverse pressure gradient caused by the crossing shock waves, the separation of the laminar boundary layer was captured near the shock waves intersection point. And the transition from laminar to turbulent occurred rapidly in the interaction region. After installation of vertex generator devices or roughness devices, the boundary layer transition position moved to the upstream of the interaction region, the separation was effectively inhibited. And the heat fluxes in the interaction region declined obviously. The peak value of heat fluxe was reduced by more than 25%. The shock wave structures and wall pressure distributions obtained from tests and simulations agreed well, while the prediction heat fluxes were much larger than the test results. The comparison between the calculated results of the transition model and the turbulence model shows that the obviously larger turbulence viscosity is the main reason why RANS methods over-predict the heat fluxes in the unseparated interaction region.

Improvement, performance test and evaluation for Schmidt–Boelter gage

ZHU Tao , YANG Kai etc.

doi: 10.11729/syltlx20220029

[Abstract](226) [FullText HTML](108) [PDF 6712KB](24)

Abstract:
A kind of the small size Schmidt–Boelter gage was improved for measuring dynamic heat flux in the continuous variable attack angle test in the conventional hypersonic wind tunnel. The Schmidt–Boelter gage improved was statically calibrated and dynamically tested by the heat flux calibration devices. The test results show that the sensitivity coefficient is 57.67 μV·kW⁻¹·m², the response time is 27 ms, the cut-off frequency is 26 Hz and the gage range coverage is 1–130 kW/m². Then the quantitative relation between the continuous variable attack angle velocity and the maximum test error was established based on the feature response time constant. And referring to the heat flux measured in the step variable attack angle test, the maximum velocity of the continuous variable attack angle supported by the gage was evaluated within a certain margin of error.

Mechanism study of free-surface polygons formation in rotating fluids

LI Weiyi , WANG Tao etc.

doi: 10.11729/syltlx20220074

[Abstract](124) [FullText HTML](60) [PDF 7871KB](11)

Abstract:
In order to study the formation mechanism of polygon phenomenon in rotating fluid, a test set-up of rotating cylinder which can produce rotating fluid was designed. Experiments on rotating fluid for different rotational frequency, liquid heights and radiuses of cylinder were performed. Based on experimental results, a composite wave theoretical model of the intersection point between the free surface of fluid and the bottom of the container was established according to the wave equation and ignoring the specific movement inside the fluid. On this basis, the theoretical model was verified by experiments, and the rotation state on the experimental phenomenon was further studied. Based on the experimental data and previous work, this paper made empirical formula fitting to the data, and found that the fitting effect of blackbody radiation model is the best. The main conclusions are shown below: 1）The viscous action caused by the relative motion between the rotating fluid and the wall causes the free surface of the fluid to form a polygon, which is related to the rotation frequency, the radius of the container, the height of the liquid surface, and the density and viscosity of the fluid, which can be shown by the phase change of the wave. 2）The radial motion of the intersection point between the free surface of the fluid and the bottom of the container can be regarded as the result of the interaction between the gravity pressure field, the centrifugal field and the reflected wave of the vessel wall and the viscous force of the vessel wall, and the radial wave equation can be approximately described by simple harmonic motion. after the parameters of the wave equation satisfy certain constraints, the free surface profile can be obtained by near Fourier transform projection. 3）For a single influence factor, the number of polygonal edges on the free surface of the rotating fluid is positively related to the rotation frequency and negatively related to the height of the liquid surface. The larger the radius of the cylinder is, the easier it is to form polygons. 4）For more influencing factors, the angle number of polygons on the free surface of rotating fluid is mainly related to the two dimensionless quantities of R/H and 1/Ek. With the increase of 1/Ek, the number of angles increases, but the range of adjacent transition boundaries decreases gradually. In the experiment, the more the number of corners, the more unstable the polygon. The disturbance caused by a slight change in rotation frequency will change the number of angles. In the experiment, there is a R/H value in the range of [2.4, 2.5], which makes polygons form most easily, and the 1/Ek range of adjacent transition boundaries is also the largest. 5）When R/H∈[2.0, 4.0], the relationship between the angle number of the rotating fluid and 1/Ek accords with the blackbody radiation model curve, which indicates that the hypothesis of the fluid complex wave may be related to the harmonic oscillator hypothesis of the blackbody radiation. When R/H>4, the constraint effect of the wall is weakened, and the blackbody radiation model can only be used for qualitative prediction. The phenomenon is explored from the theoretical point of view, and the empirical formula is fitted from the experimental point of view. The results can be further applied to theoretical research to determine the physical mechanism of the phenomenon.

Research on the dynamic derivatives test technology of 4.5 m × 3.5 m low speed wind tunnel

CHEN Hao , BU Chen etc.

doi: 10.11729/syltlx20210131

[Abstract](156) [FullText HTML](67) [PDF 7519KB](12)

Abstract:
The dynamic derivatives are the a necessary parameters in the process of analyzing the stability of the aircraft and designing the control law, in order to meet the demand for obtaining high-precision dynamic derivatives data for large-scale aircraft. Aerodynamics Research Institute of Aviation Industry Corporation of China （AVIC） developed a dynamic derivatives test system with five kinds of oscillations in the 4.5 m × 3.5 m low-speed wind tunnel. The test system uses servo hydraulic swing motor and servo hydraulic cylinder as the driving components of the motion, and directly generates arbitrary waveform motion with the control of the servo valve. The driving mode of the system has the characteristics of small movement transmission gap, high movement control precision, and high automation. The scale of the test model is up to 2.5 m, with the wind speed v =30～60 m/s, the angle of attack α= −36°～36°, and the sideslip angle β= −40°～40°. The verification tests of the dynamic standard model and a wing-body model were carried out, and the test results show that the dynamic derivatives data obtained by the test system is reasonable, the accuracy of the repeatability test data is within 3%, and the test system can provide high-quality dynamic derivatives data for large-scale aircraft.

Research on the position control of double-pass schlieren component based on visual feedback

FANG Bihong , LI Ming etc.

doi: 10.11729/syltlx20220068

[Abstract](125) [FullText HTML](63) [PDF 8409KB](7)

Abstract:
The traditional mechanical method of debugging the double-pass schlieren system exhibits the problems that the fine positioning of the working position of the spherical mirror mechanism cannot be ensured, and the optical paths cannot be completely coincided after passing through the flow field twice in the experimental application in the hypersonic low density wind tunnel. Here, a novel double-pass schlieren system based on visual feedback was developed. The system via absolute encoder instruction control the AC servo motor to adjust the position of the spherical mirror mechanism. Moreover, the pitch and left-right deflection of the spherical mirror can be adjusted by the schlieren image quality evaluation results provided by the machine vision system（visual information feedback）. The position control system of double-pass schlieren parts based on visual feedback realizes the automatic positioning closed-loop control of the double-pass schlieren spherical mirror mechanism, and ensures that the light paths overlap as much as possible after passing through the flow field twice to eliminate ghosting during imaging of the model flow field（the definition of the flow field image is improved by 2.2 times compared with that obtained by the traditional method）.

Research of the continuous scan test method for inlet in low wind tunnel

XU Binbin , LIU Tingshen etc.

doi: 10.11729/syltlx20220032

[Abstract](106) [FullText HTML](96) [PDF 6901KB](11)

Abstract:
The continuous scan test method for the inlet of airplane was studied in the FL–13 wind tunnel of CARDC. The test methods and procedures were proposed and the test data processing methods were also provided. Inlet tests were performed in the FL–13 wind tunnel to compare the conventional test method with the continuous scan test method. The test results with the continuous scan test method have a good consistency with the conventional test method, which verifies the availability and feasibility of the continuous scan test method for the inlet in the low speed wind tunnel. The research results show that the continuous scan test method can raise the tests efficiency and acquire more test data for the inlet test in the wind tunnel.

Optimization of total enthalpy measurement method based on the total temperature probe

ZHU Xinxin , LONG Yongsheng etc.

doi: 10.11729/syltlx20210149

[Abstract](186) [FullText HTML](67) [PDF 6978KB](17)

Abstract:
A kind of total temperature probe with Iridium Rhodium Iridium thermocouple is developed for improving the total enthalpy measurement accuracy. The size parameters of each component are optimized based on the fluid-thermal coupling model of the probe. The reheating rate of the probe is not less than 0.9 after optimization. The calculation and test results show that the temperature of the thermocouple node rises slowly as the temperature of the thermocouple tail and the shielding case rises. This fact results in the temperature of thermocouple node changing according to the measurement time period. So the measurement time period of the total temperature value should be regulated and the total temperature value must be calibrated. Therefore, a comparison calibration method is proposed, in which the total temperature probe used in the supersonic flow field can be traced to the standard calibration device in the subsonic flow field by an arc chamber total probe developed. Finally, the total enthalpy measurement test based on the total temperature probe is carried out in the arc heated wind tunnel. And the uncertainty of the total enthalpy measurement is calculated according to the uncertainty evaluation method based on the precision limit and deviation limit. The test results show that the total temperature probe has a high total enthalpy measurement accuracy. The repeatability precision is about 3% and the uncertainty is 6.4% in this test.

Study on interaction between wing tip vortex and flat tail tip vortex

ZHANG Zeyu , LI Dong etc.

doi: 10.11729/syltlx20210116

[Abstract](123) [FullText HTML](59) [PDF 9730KB](11)

Abstract:
The development of the wingtip vortex is an important factor for the flight safety and airport efficiency of the aircraft landing on the runway. The near-field characteristics of the wingtip vortex mainly determine the vorticity of the vortex in the landing phase. In this paper, a simplified model of A320 is used as the object to observe the near-field configuration of the wingtip vortex in a low-speed tunnel of 1 m × 1 m. It is found that the horizontal tail vortex rotates around the wingtip vortex, and the rotational angular velocity in different flow stations is different. By comparing the simulation results, it is found that the rotational angular velocity of the horizontal tail vortex around the wingtip vortex is basically consistent with the experimental results, indicating that the development of the wake vortex under different Reynolds numbers has certain similarity in the characteristics of the rotational angular velocity between two vortices.

Flash infrared thermal wave detection of Ice surface edge

GOU Yi , LI Qingying etc.

doi: 10.11729/syltlx20220017

[Abstract](146) [FullText HTML](104) [PDF 7607KB](9)

Abstract:
Ice accretion detection is an important means to ensure flight safety and an important issue in the field of aircraft anti-icing. In this paper, the method of identifying the boundary between the ice surface and the interior is discussed by using the infrared thermal wave detection technology. With a flash infrared thermal wave detection system established, regular ice accretion samples and ice accretion samples with internal boundary were made, the ice accretion detection experiments were carried out, and the data of the infrared thermal wave sequence were collected. In addition, the traditional algorithm based on the first-order differential operator and the second-order differential operator was exploited for processing the ice edge. A new boundary recognition method was proposed as well, which combined the gauss-Pierre-Simon Laplace pyramid algorithm and the area filtering algorithm. Then, the feasibility of the proposed algorithm to identify the boundary of the ice accretion surface was discussed and compared. The experiments and the image data processing methods show that the traditional algorithm can successfully recognize the outer boundary of ice accretion, but can not accurately recognize the internal boundary of ice accretion. The new fusion algorithm can effectively recognize the ice edge and the internal boundary, but the image noise is higher than that of the traditional algorithm. It can be concluded that the new fusion algorithm has some advantages in the detection of the irregular icing surface, and it is expected to provide a new research idea for icing detection in the field of aircraft anti-icing.

Wind tunnel force test of fairing separation in hypersonic and high dynamic pressure situation

ZHONG Jun , LIN Jingzhou etc.

doi: 10.11729/syltlx20210194

[Abstract](288) [FullText HTML](147) [PDF 9052KB](27)

Abstract:
For the problem of the monolithic fairing separating from a hypersonic test demonstrator in a high dynamic situation, the reverse-thrust jets simulation method and wind tunnel force test model design have been developed, to meet the requirements of simulating the jets interaction effect and separation distance influence in the hypersonic wind tunnel. The fairing’s aerodynamic characteristics, including the jets interaction effect and the separation distance influence, were obtained by the strain balance in circumstances where the Mach number of the free-stream was 5 and the dynamic pressure was 33 kPa. The study indicates that the jets interaction effect dominates fairing’s aerodynamic characteristics in the separation process. The maximum coefficients’ variation of the normal force, axial force and pitching moment are 44.5%, 32.4% and 198.6% respectively. The pressure center moves forward obviously, making the fairing with designed static stability presents un-stability features in the minus attack angles. The influence of the separation distance on fairing’s aerodynamic characteristics becomes weaker as the separation distance increases. Using a small positive angle as the initial separation attack angle is helpful for the fairing maintaining a stable attitude, benefitting separation security during the separation process.

Simulation and fabrication of bionic sharkskin composite micro-nano wind resistance reduction structure

XU Zheng , LIU Ri etc.

doi: 10.11729/syltlx20220002

[Abstract](683) [FullText HTML](210) [PDF 9375KB](42)

Abstract:
The combination of bionics and drag reduction technology has opened up an important research direction in the field of drag reduction, and has made a significant breakthrough. For better implementation to reduce the wind resistance effect, this paper studies the composite micro-nano drag reduction structure, according to the principle of bionics, through CFD simulation combined with the laser micro-nano fabrication technology. A combined model of drag reduction structure wad established. The flight vehicle air sensor head surface with bionic sharkskin composite micro-nano structures was manufactured by laser interfernce scanning on the basis of the bionic sharkskin scale structures, to further improve the drag reduction performance. Through the parallel simulation and wind tunnel test, the drag reduction mechanism was theoretically analyzed, and the composite structures were manufactured with a drag reduction rate of up to 10.3%.

A bi-weighted-POD and its application on wind pressure field

ZHANG Hao , YANG Xiongwei etc.

doi: 10.11729/syltlx20210146

[Abstract](148) [FullText HTML](188) [PDF 7426KB](7)

Abstract:
Proper Orthogonal Decomposition（POD） is a reduced order modeling（ROM） method based on 2nd-order statics, which simplifies the investigated wind-pressure field in a new coordinate system formed by a set of orthonormal basis. This paper suggests a method of bi-weighted POD（which weights POD by area and at the same time by root-mean-square）, and applies this method to the modal reduction of pressure field around buildings. Firstly, we introduce the POD expansion in a mean-square method, which demonstrates that POD is the optimal choice of ROM in the mean-square sense. Furthermore, we modify the original POD by the bi-weighting-method to improve its capacity of identifying coherent structures with lower energy in pressure field. For the last part, the validity of bi-weighted POD is roughly examined by a case study which applies the method to the pressure field of a 5∶1 rectangular cylinder. It turns out that the modified POD method improves the ROM accuracy at the area associated with lower energy in a significant way. In the meantime, a wind-pressure field ROM constructed by bi-weighted POD captures vital information provided by the original wind-pressure field and is spatially accuracy-consistent.

Experimental study on high frame rate characteristics of dynamic flow field of jet in crossflow

WANG Zhen , WANG Yayao etc.

doi: 10.11729/syltlx20210077

[Abstract](286) [FullText HTML](121) [PDF 15431KB](33)

Abstract:
Despite the decisive influence of various vortex structures of a jet in crossflow on the jet trajectory and scalar mixing, there are few studies related to the high-frequency dynamic characteristics of shear-layer vortexes during transportation. This paper focuses on the high-frequency flow field characteristic, the scalar concentration distribution and the formation and collapse process of the turbulent microstructure of the jet in crossflow with different nozzle diameters and velocity ratios using 40 kHz particle image velocimetry（PIV） and 20 kHz acetone planar laser induced fluorescence（PLIF）. The experimental measurements of the velocity and scalar field show that: increasing the velocity ratio promotes the expansion of the circulation zone behind the jet; in the near field of the jet trajectory, power law fitted velocity distribution and shear-layer vortex trajectory shows an exponentially decrease of the jet velocity, the shear-layer vortex strength and vortex motion frequency also show a downward trend, with the frequency of the shear-layer vortex on the windward side slightly lower than that on the leeward side; as the jet velocity increases, the frequency of the shear-layer vortex increases gradually, but the Strouhal number decreases.

Development of high-precision micro-rolling moment gas bearing balance

ZHANG Huangwei , XIANG Guangwei etc.

doi: 10.11729/syltlx20210182

[Abstract](259) [FullText HTML](97) [PDF 6260KB](19)

Abstract:
During the reentry process of the miniaturized reentry vehicle, small asymmetry of its shape can be produced due to surface ablation, resulting in a small rolling moment. In order to obtain the high-precision micro-rolling moment measurement data of the ablation model of the miniaturized reentry vehicle in the hypersonic wind tunnel, and obtain the other five component aerodynamic data, a six component micro-rolling moment gas bearing balance was developed. The rolling moment design load of the balance is 0.02 N·m, and the axial force design load is 200 N, which are orders different from each other. The overall force measurement scheme of “4+2” balance is proposed, where the four component main balance elements cooperate with the two-component M_x-X elements to complete the extremely mismatched six component aerodynamic measurement. The results of the static calibration and the wind tunnel test show that the balance has good resolution and strong anti-interference ability, and is little affected by temperature. The measurement results of the rolling moment coefficient reach the order of 10^–7. The developed gas bearing balance is little affected by the temperature and can be reused. It can measure the six components of aerodynamic data including the micro-rolling moment at the same time, which greatly improves the test efficiency and reduces the error caused by model disassembly.

A concise method of determining critical flutter wind speeds for small damping modes

TANG Jianping , HE Jun etc.

doi: 10.11729/syltlx20210071

[Abstract](270) [FullText HTML](89) [PDF 6600KB](6)

Abstract:
In low speed flutter tests, flutter models with small damping modes start continuous vibration usually at low speeds without obvious flutter divergence. Therefore, it’s of some uncertainty on determing the critical flutter wind speeds by visual inspection or by “damping method （DM）” of modal parameter identification. Considering the similarity between the vibration phenomenon of a small damping modal flutter test and that of a fighter buffet test, a technique named “amplitude turning point method （ATPM）” similarly to that used in identifying buffet boundaries is proposed to determine the critical flutter wind speeds. The method is based on RMS of vibration amplitudes, the curves of normalized vibration RMS changing with wind speeds are drawn, and critical flutter wind speeds are determined according to the first turning points of curves. In a small damping modal flutter test, the method was applied in the test data processing of the engine hangers with variable parameters. Comparing the ATPM results with the DM results and the numerical results, the following conclusions are made: the results of three methods are in agreement, the ATPM results are more similar to the numerical results than the DM results, and the ATPM is concise and reliable, with good stability and applicability.

Contents

2023, 37(4).

Abstract(2) PDF(1)

Abstract:

A review on the development of oscillating jets

WU Mengwei , XU Minyi et al.

2023, 37(4): 1-17. doi: 10.11729/syltlx20230022

Abstract(7) HTML(1) PDF(3)

Abstract:

The flow control method can effectively promote the mixing of the injected fluid with the surrounding fluid, and it has important applications in various fields, such as energy, chemical industry, aerospace and precision manufacturing, etc. Therefore, it has received widespread attention from scholars worldwide. In order to better understand the current situation and future development trend of oscillatory jets, this paper is the first to comprehensively summarize and classify the seven excitation methods of oscillatory jets, such as microjet, mechanical, feedback, blunt V-nozzle, impact V-plate, cavity self-excited flapping, film self-excited flapping, etc. A comparison of the principles of the different excitation methods and the characteristics of the resulting oscillating jets is conducted, pointing out the problems of the oscillating jet technology itself and the limitations of the industrial application of related technologies, and giving forecasts and suggestions for the development of the oscillating jet technology.

Effect of flow around a wall-mounted 2D square cylinder on WSS in a TBL

ZHANG Zhihao , FU Qixing et al.

2023, 37(4): 18-28. doi: 10.11729/syltlx20230035

Abstract(54) HTML(23) PDF(32)

Abstract:
In this paper, the effect of flow around a wall-mounted 2D square cylinder on WSS (Wall Shear Stress) in a TBL (Turbulent Boundary Layer) is studied using TR–PIV and hot wires. The Reynolds number, defined by the cylinder width and the free stream velocity, is fixed at 1.1 × 10⁴. There exist two types of large-scale flow structures, i.e., vortex I which denotes those moving towards the wall, and vortex II which denotes those moving downstream. The flow structures have significant effects on the flow and WSS: increasing the streamwise velocity gradient that results in a sharply increased WSS; reducing the streamwise velocity gradient that results in a sharply decreased WSS; and changing the WSS direction. The study is helpful to understand the physics of surface erosion, pollutant accumulation, flow energy loss, etc.

Research progress on rotor reverse flow and dynamic stall flow control methods

LI Guoqiang , ZHAO Xinhai et al.

2023, 37(4): 29-47. doi: 10.11729/syltlx20230054

Abstract(41) HTML(11) PDF(16)

Abstract:
When a helicopter flies forward at high speed with heavy load, the blade pitch changes greatly and dynamic stall is prone to occur. The lower rotational speed of the inner section of the trailing blade leads to the formation of a reverse flow zone under the superposition of the incoming flow, resulting in a reduction in the aerodynamic efficiency of the blade. The problems of blade fatigue failure and lift reduction hinder the further improvement of helicopter performance. Flow control methods have great potential in improving the aerodynamic characte-ristics of airfoils, and are effective ways to improve the rotor aerodynamic efficiency and ensure helicopter safety and stability. In this paper, the formation mechanism and unsteady flow characteristics of the reverse flow zone and dynamic stall are firstly described, and the research results of two special aerodynamic phenomena are summarized. On this basis, a comparative analysis of flow control methods such as variable airfoil configuration, surface mechanical devices, air-blowing control, plasma actuator, synthetic jet actuator, and trailing edge flap on the mechanism of rotor dynamic stall and reverse flow control is conducted, and the effects of control parameters and flow field parameters on control effectiveness are summarized. Finally, the remain-ing problems and solutions in the application of various flow control methods are prospected.

Flowfield and friction characteristics downstream of mirco vortex generator in turbulent boundary layer

ZHANG Yi , PAN Chong et al.

2023, 37(4): 48-58. doi: 10.11729/syltlx20230027

Abstract(10) HTML(0) PDF(3)

Abstract:
The present work uses the stereoscopic particle image velocimetry and calibration-free dual hot-film wall shear stress measurement sensor to measure the flowfield and friction at downstream of the one array of forwards wedge Micro Vortex Generator (MVG) in the turbulent boundary layer at moderate Reynolds number. The result of flowfield measurement shows that MVG produces the streamwise velocity defect regions and streamwise vortices pairs in downstream time-averaged flowfield, which causes the second outer-peak in the spanwise pre-multiplied energy spectra. The result of proper orthogonal decomposition shows that the contribution of energy of structures induced by MVG is equivalent to the that of large-scale structures and very large-scale structures in the smooth-wall turbulent boundary layer, which also significantly affects the spatial distribution of the near-wall structures. The friction measurement experiment shows that MVG array with higher height and closer spanwise arrangement has higher friction drag reduction. The drag reduction effect of MVG lasts downstream to 80 times of its own characteristic height.

AI-based real-time noise reduction of flow field pressure signals under plasma electromagnetic interference

CHEN Jie , ZONG Haohua et al.

2023, 37(4): 59-65. doi: 10.11729/syltlx20230030

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Abstract:
For the reliable sensing requirements of closed-loop active flow control, a real-time noise reduction method based on the artificial neural network was proposed for solving the plasma actuation electromagnetic interference on flow field signals. Taking the dynamic pressure sensor installed on the cylinder surface as the experimental subject, the “dense peak” type noise signals of alternating current dielectric barrier discharge (AC–DBD) and the “sparse spike” type noise signals of nanosecond pulsed dielectric barrier discharge (NS–DBD) were collected respectively. Artificial synthetic noise signals were used for supervised learning, and the generalization of the artificial neural network model was tested and verified. The results show that this method can effectively suppress the influence of electromagnetic interference caused by plasma actuation and restore the real pressure signal. It has better denoising performance on the AC–DBD “dense peak” type noise signal. The denoised signal is smoother and better fitted with the real one. This model is also applied to the real flow field pressure measurement, and the accuracy of the denoising network prediction is further verified by comparing the mean value of the denoised signal and the real signal.

Passive control on flow past a circular cylinder with bionic nylon wires

CHEN Wenli , LIN Longhan et al.

2023, 37(4): 66-75. doi: 10.11729/syltlx20230019

Abstract(40) HTML(11) PDF(8)

Abstract:
We investigated the control effectiveness and mechanism of the control of the circular cylinder flow field using bionic nylon wires inspired by bird feathers by wind tunnel tests. In this experiment, at a Reynolds number of 2.67 × 10⁴, the bionic nylon filament was arranged at the front station of the cylinder and the length ratio L/D between nylon wire length and cylinder diameter was used as the characteristic parameter. The surface pressure measurement system was used to obtain the pressure coefficients around the cylinder to analyze the aerodynamic forces acting on the cylinder. The two-dimensional flow field information of the cylinder was obtained by a high-speed Particle Image Velocimetry (PIV) measurement system, and the Proper Orthogonal Decomposition (POD) was used to obtain the instantaneous and time-averaged characteristics of the flow field. The results show that at L/D < 0.6, the control effectiveness of nylon wires is limited because the nylon-induced vortex structures cannot reach the wake field. At L/D > 1.0, the nylon wires can significantly reduce the turbulent kinetic energy and Reynolds stress of the cylindrical wake field and suppress the lift and drag coefficient distributions around the circular cylinder. And at high values, nylon wires can inhibit the interaction between shear layers and thus change the von Kármán vortex shedding pattern of the cylinder.

Investigation on performance enhancement of flap based on dual synthetic jets

ZHANG Jianyuan , LUO Zhenbing et al.

2023, 37(4): 76-86. doi: 10.11729/syltlx20230046

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Abstract:
When the aircraft is in the process of taking off, landing and flexible maneuvering, flow separation occurs above the flap and rudder which is caused by the large deflection angle. It reduces the performance of the flap and rudder, or even makes them ineffective. In order to solve this problem, a performance enhancement technology of flap based on array dual synthetic jets was proposed. Aiming at seamless flap, the influence of different dual synthetic jets driving parameters on the lift force and flap performance was investigated. The investigation results show that the dual synthetic jets can generate periodic vortex structures above the flap surface, which enhanced the momentum exchange between the low-velocity air in the boundary layer and the main flow. These vortex structures can also strengthen the ability of the boundary layer to resist the adverse pressure gradient. The array dual synthetic jets at the flap can effectively increase the lift force and enhance the flap performance. The flap performance enhancement is more effective when the dimensionless driving frequency is 3.89 and the momentum coefficient is 3.01 × 10^–3. The integrated model of the array dual synthetic jets actuator combined with the wing was designed and fabricated, and the flight test was carried out. The rolling angular velocity could achieve 15.69 (°)/s, which verifies the feasibility and effectiveness of performance enhancement of flap based on dual synthetic jets.

Practices and challenges on PIV technology in high speed complex flows

Liu Hong, Chen Fang, Li Xiaojie, Zheng Zhonghua, Xiao Baoguo

2016, 30(1): 28-42. doi: 10.11729/syltlx20150069

[Abstract](344) [PDF 6594KB](48)

摘要：
粒子图像测速技术目前已经发展成为实验流体力学领域应用最广泛的非接触激光测试方法之一,为认知复杂流动机理提供直观的流场信息.本文基于超声速流场PIV技术研究实践,针对示踪粒子布撒器设计、粒子松弛特性模型构建、激波流场测试分析、超声速平板湍流边界层结构分析等方面具体问题的研究和认识,从理论、定量化的角度深入分析了应用于超声速流场PIV技术现阶段依然存在的问题.从应用于超声速流场PIV技术的原理出发,针对高速复杂流场的PIV测试现状,总结了应用于超声速流场PIV技术发展过程中的光学部件、示踪粒子及布撒系统所遇到的一系列挑战,以及国内外利用PIV技术在高速复杂流场研究中所取得的成就,针对PIV技术能否适用于高超声速流场的测量做了系统化地探索.并根据实践经验提出了应用于超声速流场PIV技术未来的发展方向:通用的精确的PIV方法不存在,必须从具体研究的流动机理角度改造相应的PIV测试手段.

Experimental study on Reynolds number effect on aerodynamic pressure and forces of cylinder

Liu Qingkuan, Shao Qi, Zheng Yunfei, Li Conghui, Ma Wenyong, Liu Xiaobing

2016, 30(4): 7-13. doi: 10.11729/syltlx20150112

[Abstract](432) [FullText HTML](145) [PDF 10428KB](17)

摘要：
通过刚性模型测压风洞试验，研究了圆柱的气动阻力、气动升力系数和风压系数随雷诺数的变化规律，从流场分布的角度分析了气动力变化的原因，并研究了雷诺数影响下的流场在圆柱轴向的相关性。结果表明：在亚临界雷诺数区域，在时间平均上流场沿模型两侧呈对称分布，雷诺数对平均阻力系数和流场影响较小，平均升力系数基本为零。在临界雷诺数区域，随着特定区域大负压区的出现，流场不再对称，出现不容忽视的平均升力和脉动升力。在超临界雷诺数区域，随着对称侧大负压区的出现，流场恢复对称状态，平均升力基本消失。雷诺数对流场的轴向相关性有显著的影响。在雷诺数较低时（亚临界区域），卡门涡在轴向上的尺度相对较大，而随着雷诺数的提高，该尺度逐渐减小，各断面流场的相关性降低。

Experimental investigation on the aerodynamics of tunnel-passing for high speed train with a moving model rig

Song Junhao, Guo Dilong, Yang Guowei, Yang Qiansuo

2017, 31(5): 39-45. doi: 10.11729/syltlx20170002

[Abstract](205) [FullText HTML](114) [PDF 10066KB](5)

摘要：
高速列车进入隧道时，会产生压缩波，压缩波沿隧道内传播至隧道端口后形成向外辐射的微气压波。本文介绍了采用动模型实验平台在200~350km/h速度范围内对60m双向隧道模型的隧道壁面压力波和出口微气压波开展的实验研究。首先分析了实验数据的有效性；其次给出了初始压缩波最大值随时间的衰减变化规律和微气压幅值随实验速度的变化特性；最后研究了流线形头型长度对微气压波幅值的影响。实验结果表明：在实验速度范围内，隧道压力波和出口微气压波无量纲值保持一致，但隧道出口微气压波与流线型头型长度只能定性描述，定量关系难以确定。

Research progress of aerodynamic thermal environment test and measurement technology

Zhu Guangsheng, Nie Chunsheng, Cao Zhanwei, Yuan Ye

2019, 33(2): 1-10. doi: 10.11729/syltlx20180137

[Abstract](384) [FullText HTML](204) [PDF 13536KB](69)

摘要：
地面风洞试验和飞行试验是研究高超声速飞行器气动加热的主要手段。针对临近空间复杂气动外形高超声速飞行器气动热环境研究的需要，分析探讨了国内气动热试验及测量技术的发展情况。分析了临近空间高超声速飞行器外形特征以及飞行剖面、边界层转捩和气动热环境特性等，进而分析了气动热环境风洞试验模拟理论，介绍了适用于气动热研究的风洞试验设备及其模拟能力，重点讨论了适用于不同类型风洞的热流测量技术发展近况、存在的问题和发展趋势；在以长时间、高热流、高壁温为主要特征的高超声速飞行试验中，无法应用风洞环境下的热流测量技术，因而介绍了目前飞行试验中采用的气动热测量技术，讨论了根据结构温度反辨识表面热流存在的问题，以及热流传感器表面的"冷点效应"、表面催化特性等因素对飞行试验气动热测量的影响，提出了后续工作中应重点研究和解决的临近空间飞行器气动热环境测量技术问题。

PIV measurement and numerical simulation of Taylor-Couette flow

Feng Junjie, Mao Yuhong, Ye Qiang, Liu Renhong, Chang Qing

2016, 30(2): 67-74. doi: 10.11729/syltlx20150091

[Abstract](514) [PDF 5952KB](34)

摘要：
采用粒子成像速度场仪(PIV)和数值模拟(CFD)对Taylor-Couette 流场进行测量,获得各转速下涡流场信息。将同等条件下PIV测量结果与数值模拟结果相联系,对比分析不同旋转雷诺数范围内涡流场中不同径线和中轴线上各向速度的变化特征。结果表明,各种特征存在一定的转速分段范围:在2~7r/min(Re为100~350)时,各向速度特征为层流涡特性,在7~40r/min(Re为350~2000)时,各向速度特征为波状涡特性,在40~60r/min (Re为2000~3000)时,各向速度特征为调制波状涡特性,当转速大于60r/min(Re大于3000)时,各向速度特征为湍流涡特性。根据不同角度获得的各向速度特征对应的内筒转速、旋转雷诺数与流场涡形态的关系,明确分析出特定几何条件下,泰勒涡发生形态转变的旋转雷诺数,以便于深入探究泰勒涡流场的特性,定量分析涡运动形态特征。

Effects of end plates on aerodynamic force of rectangular prisms in wind tunnel test

Zheng Yunfei, Liu Qingkuan, Ma Wenyong, Liu Xiaobing

2017, 31(3): 38-45. doi: 10.11729/syltlx20170015

[Abstract](469) [FullText HTML](195) [PDF 1175KB](13)

摘要：
在节段模型风洞试验中，两端设置端板可以有效减小端部效应对风压分布的影响，从而保证气流在模型周围的二维流动，其中端板尺寸是影响端板效果的主要参数。为了明确不同尺寸端板对矩形断面气动特性的影响，以桥梁节段模型中最常见的3种宽高比（B/H分别为1、5和10）的二维矩形断面为研究对象，通过刚性模型测压试验，研究了端板尺寸对各模型的气动力、风压分布和斯托罗哈数St的影响。研究结果表明：模型的端部效应不仅仅对端部附近的风压有影响，对中间位置处风压的影响也不容忽视，设置端板是获得准确试验结果的重要保证；随着断面宽高比（B/H）逐渐增大，端部效应影响的程度和范围逐渐减小；随着端板尺寸的增大，模型背风面风压绝对值逐渐增大并趋向一稳定值；抑制端部效应的最小端板尺寸与结构的风迎角有关，风迎角增大，所需的端板也相应增大；有无端板对斯托罗哈数St也有明显影响。

Review of research on the receptivity of hypersonic boundary layer

Jiang Xianyang, Li Cunbiao

2017, 31(2): 1-11. doi: 10.11729/syltlx20160129

[Abstract](567) [FullText HTML](206) [PDF 7434KB](83)

摘要：
高超声速边界层感受性是边界层转捩预测与控制的关键环节，其对高超声速飞行器研究至关重要。目前关于高超声速边界层感受性的实验研究仍然十分匮乏，为了更好地理解高超声速边界层感受性过程并指导该领域的实验研究，文章梳理了近20年来国际上高超声速边界层感受性问题的研究内容，包括对自由流扰动和壁面扰动的感受性，并主要介绍了Fedorov的前缘感受性理论和模态转化机制。最后总结了自由流扰动中感受性的不同发展路径。

Investigation of several fundamental combustion problems in rocket-based combined-cycle engines

He Guoqiang, Qin Fei, Wei Xianggeng, Cao Donggang, Huang Zhiwei, Liu Bing

2016, 30(1): 1-14,27. doi: 10.11729/syltlx20150159

[Abstract](452) [PDF 6603KB](19)

摘要：
火箭冲压组合发动机包含多个工作模态,不同模态灵活组合的优势使其具有宽速域和广空域的工作特点,兼具加速和巡航的优点.火箭冲压组合发动机燃烧室中存在着亚声速、跨声速和超声速共存的流动结构,具有流动速度高、混合时间短、反应强度大、燃烧空间受限和波系结构复杂等特点.围绕火箭射流的强剪切性、燃烧模式的多样性和燃烧过程的动态性,分析了火箭冲压组合发动机的流动与燃烧特征,总结了面向发动机的高速湍流燃烧研究进展,研究了火箭冲压组合发动机中超声速反应混合层的生长特性、燃烧模式与空间释热分布和动态燃烧特性等问题.通过对碳氢燃料详细化学动力学机理的简化、校验,获得了分别适合于工程计算和细致燃烧机理研究的总包反应与框架机理.从火箭射流主导的反应混合层生长模型,宽范围、变来流工作中流动燃烧过程的不确定性和碳氢燃料动力学的简化与加速算法研究出发,提出了火箭冲压组合发动机基础研究中需要突破的问题,为认识发动机中多尺度燃烧机理、优化多模态燃烧组织提供参考.

Experimental study on the flow past a rotating cylinder with PIV

Sun Jiao, Zhang Bin, Tang Zhanqi, Chen Wenyi

2016, 30(1): 81-90. doi: 10.11729/syltlx20150037

[Abstract](306) [PDF 4386KB](17)

摘要：
投弃式海流剖面仪(Expendable Current Profiler,XCP)周围流场是典型的旋转圆柱绕流.探头周围流场对探头的运动状态起决定性作用,这直接关系到探头的测量性能,因此有必要对旋转圆柱周围流场进行实验研究.实验在循环水槽中进行,通过PIV对雷诺数保持不变(Re=1000)、不同圆柱旋转速度比(α=0、0.5、1.0、1.5、2.0、2.5、3.0、3.5、4.0、4.5和5.0)的圆柱下游尾流场进行研究.通过选取不同旋转速度比的任一时刻的瞬态流场,来分析旋转对圆柱尾流结构的影响.为了获得流场的频率信息,对所获得流场信息进行能谱分析来获取涡旋的脱落频率,并进一步使用正交模态分解对流场进行分析,给出了流场主要拟序结构及其能量与转速比的变化趋势.发现圆柱旋转改变圆柱尾流结构,使尾迹尺度变小.在旋转速度比0≤α≤2.0时,存在明显的周期性涡旋脱落,并且涡旋脱落的频率有逐渐升高的趋势;而且当转速比2.0<α≤5.0时尾迹流场的周期性减弱,涡旋脱落变得不明显,流场表现出低频、剪切层的区域特征.随着转速变大,涡旋尺度变小.在较高旋转速度比时,流场中能量被重新分布.

Measurements of circular cylinder's wake using time-resolved PIV

Wang Yong, Hao Nansong, Geng Zihai, Wang Wanbo

2018, 32(1): 64-70. doi: 10.11729/syltlx20170099

[Abstract](534) [FullText HTML](333) [PDF 9648KB](32)

摘要：
采用时间解析PIV（采样频率为1000Hz）在0.55m×0.4m声学风洞中测量了直径D=20mm圆柱后方7.5倍直径、圆柱两侧各3.3倍直径所围成范围内的绕流尾迹在雷诺数Re=2.74×10⁴下的非定常流场。针对PIV获得的速度场数据，进行流场和频谱特性分析，探讨了圆柱绕流尾迹中的平均流场和脉动流场特性，以及旋涡脱落的频率特性。提出了基于速度场之间相关性的相位平均分析方法，系统分析了圆柱上下两侧旋涡交替生成、脱落、发展并耗散的完整演化过程。结果表明：在圆柱后方存在一个低速回流区，其中心0.8D的位置附近是流动结构变化最剧烈的区域；圆柱后方1.9D位置附近是上/下两侧脱落旋涡交汇、耦合的区域，湍流脉动最强；圆柱绕流尾迹中，旋涡脱落频率对应的斯特劳哈尔数稳定在0.2左右；基于速度场之间相关性的相位平均分析方法简单有效，可以准确地识别绕流尾迹中旋涡交替脱落和发展的时空演化过程，在非定常流场测量方面具有普遍推广意义。

A review on flow field velocimetry based on high-speed schlieren/shadowgraph systems

ZHU Haijun, WANG Qian, MEI Xiaohan, WU Yu, ZHAO Changying

2022, 36(2): 49-73. doi: 10.11729/syltlx20210110

[Abstract](3484) [FullText HTML](877) [PDF 8779KB](877)

Abstract:
The 2-Dimensional （2D） and 3-Dimensional （3D） velocimetry based on schlieren/shadowgraph methods are reviewed in this article. The main content includes the basic optical setups and principles of schlieren and shadowgraph systems, as well as the velocimetry algorithms. For 2D measurement, there are mainly two types of velocimetry algorithms: one is cross-correlation algorithm adopted by PIV, while the other is the optical flow method. The basic formulas, advantages and limitations are introduced comparatively. A recent developed schlieren motion algorithm can provide high accuracy and dense estimation, which is promising and applicable in a wide range of applications. The 3D reconstruction and particle tracking algorithms highly rely on the systems. In this review, three different setups are introduced, including tomographic shadowgraphy, two-view collimated light path shadowgraphy and two-view converging path shadowgraphy. The two-view systems are more concise in setup, requiring less equipment, which are advantageous for high-speed measurements. The 3D particle tracking algorithms of two-view systems are introduced, while the main focus is placed on the image space-based tracking algorithms and the spatial-temporal tracking methods. The latter introduces the temporal predictions into the stereo matching process. The particle reconstruction and tracking correctness in dense particle situations is improved significantly by using the strongly coupled spatial and temporal constraints for optimisation. Its performance is superior to several artificial intelligence methods. The progress of the velocimetry algorithms, together with the imaging advantages of short exposure and high-frequency framing rate, has promoted schlieren/shadowgraph from conventional flow visualization to advanced velocimetry techniques, which can play a role for experimental study in a wide range of complex turbulent and transient flow conditions.

Recent advances in background oriented Schlieren and its applications

XIONG Yuan

2022, 36(2): 30-48. doi: 10.11729/syltlx20210173

[Abstract](2911) [FullText HTML](1088) [PDF 7889KB](1088)

Abstract:
Background oriented Schlieren （BOS） has appeared near 2000 as a variant of the classical schlieren technique. It is a new non-intrusive optical diagnostic technique for measuring the refractive index of complex flows quantitatively. Compared to knife-edge and rainbow Schlieren, BOS is advantageous in terms of optical alignment, systematic calibration, and the dimension of the field of view. The principle and the essential system parameters of BOS are introduced in detail. An overview of recent advances in the BOS technology is presented according to the typical sequence of setting up a BOS system. Finally, recent applications of BOS in super/hypersonic flows, combustion, and plasma flow environments are also introduced.

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