Flash infrared thermal wave detection of Ice surface edge
GOU Yi , LI Qingying etc.
 doi: 10.11729/syltlx20220017
[Abstract](26) [FullText HTML](13) [PDF 7607KB](2)
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.
Research on ultra low dew point in-situ on-line measurement technology for cryogenic wind tunnel
WANG Bin , XU Zhenyu etc.
 doi: 10.11729/syltlx20210062
[Abstract](24) [FullText HTML](15) [PDF 8342KB](2)
Abstract:
To achieve wide temperature domain, high precision and ultra low dew point in-situ on-line measurement in the cryogenic wind tunnel, a technology based on the laser absorption spectrum is developed. In the method, the principles of laser absorption spectroscopic technology for dew point measurement are analyzed firstly. Then the absorption spectroscopic selection, spectral parameter calibration and spectral signal processing are provided. The experiments are carried out on the low temperature platform and in the 0.3 m cryogenic wind tunnel, which are compared to the chilled-mirror dew-point hygrometer measurement. The experimental results show that the developed technology can achieve wide temperature domain, high precision and in-situ on-line dew point measurement. The measurement range is from –100 ℃ to 30 ℃, the error is less than 1 ℃, and the time is less than 1 s. It can be used for ultra low dew point in-situ on-line measurement in the cryogenic wind tunnel.
Wind tunnel force test of fairing separation in hypersonic and high dynamic pressure situation
ZHONG Jun , LIN Jingzhou etc.
 doi: 10.11729/syltlx20210194
[Abstract](53) [FullText HTML](14) [PDF 9052KB](4)
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](77) [FullText HTML](30) [PDF 9375KB](11)
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](25) [FullText HTML](11) [PDF 7426KB](2)
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.
Direct connected experimental research on hydrocarbon-fueled rotating detonation
WANG Chao , ZHENG Yushan etc.
 doi: 10.11729/syltlx20210086
[Abstract](296) [FullText HTML](69) [PDF 8458KB](45)
Abstract:
Direct connected tests of rotating detonation were performed with ethylene and room-temperature kerosene adopted as fuel. The corresponding flight velocity is Ma 5, and the Mach number is 2.5 at the isolator entrance. Results show that the rotating detonation wave was sustained after initiation with the equivalent ratio of ethylene ranging from 0.43 to 0.99. The propagation frequency of detonation waves is 5.32–6.42 kHz, with a propagation cycle of 0.156–0.188 ms. As the equivalent ratio increases, the propagation velocity of the detonation wave and the pressure in the detonation combustor increase almost linearly. While the averaged pressure peaks of the dynamic pressure(PCB pressure sensor) first increase and then decrease. The pressure at the isolator exit also increases under a higher equivalent ratio, but the velocity remains unchanged at Ma 2.5. When the equivalent ratio of kerosene was about 0.70, the rotating detonation wave was also sustained.
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](64) [FullText HTML](16) [PDF 15431KB](9)
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](68) [FullText HTML](20) [PDF 6260KB](5)
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 Mx-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](65) [FullText HTML](23) [PDF 6600KB](2)
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.
Design and application of the dynamic stage separation device in hypersonic wind tunnel
HE Chao , SUN Peng etc.
 doi: 10.11729/syltlx20200119
[Abstract](89) [FullText HTML](52) [PDF 6471KB](13)
Abstract:
In order to study motion characteristics of the separation between the cruise stages and booster stages, it is needed to develop the device of the dynamic stage separation for the dynamic stage separation wind tunnel test. Hypervelocity aerodynamics institute of CARDC studied and developed the dynamic separation device aimed at application in routine hypersonic wind tunnels, which includes the support system of dynamic separation and the dynamic stage separation support and release device. In the design, the finite element analysis is used to evaluate the characteristics of the support structure. The analysis contains the inherent frequency analysis. The vision measurement system is used to measure the trajectory and the runtime of the dynamic stage separation support and release device. The runtime is 78 ms, which satisfies the requirement of the wind tunnel test. Finally a series of wind tunnel tests were conducted in the hypersonic wind tunnel. The results of computation and the wind tunnel test indicate that: the inherent frequency of the support structure, and the runtime of the dynamic stage separation support and release device, which is 78 ms, can satisfy the need of the wind tunnel. According to the different particular wind tunnel circumstances, the size of the dynamic separation device can be reformed, which can be applied to different hypersonic wind tunnels.
Experimental study of the effects of confinement on self-sustained oscillations and noise radiation in three-dimensional open cavities
WANG Chao , YUE Tingrui etc.
 doi: 10.11729/syltlx20210050
[Abstract](140) [FullText HTML](50) [PDF 9212KB](12)
Abstract:
Flow past an open cavity has been studied extensively, while less attention has been paid to the effects of confinement due to side walls, which produces rich flow dynamics and noise characteristics. In this study, the effects of confinement on flow structures and noise radiation in three-dimensional rectangular cavities are investigated experimentally. The length and depth are fixed, and five ratios of width/length (W/L=0.1–0.5) are considered. The measurements are performed in an acoustic wind tunnel. The pressure oscillations are onset after the wind speed is greater than Ma 0.03. Once the wind speed is greater than or equal to Ma 0.20, the flow and noise radiation are dominated by the self-sustained oscillations corresponding to the second Rossiter’s mode. Furthermore, the present experiments show that the local pressure oscillations and noise radiation of this frequency can be weakened or even eliminated when W/L is equal to or less than 0.3 for the wind speeds of Ma 0.20 and Ma 0.25. The upstream OASPLs in the far field can be reduced by more than 3 dB when W/L decreases from 0.4 to 0.3 at Ma 0.20. By analyzing the surface pressure and TR-PIV(Time-Resolved Particle Image Velocimetry) results, it is found that the suppression of the tonal noise is closely related with the changes of the primary recirculation and some secondary vortical structures by decreasing W/L. In particular, the intensity of the primary recirculation is greatly weakened with strong confinement effects, and the feedback process is not strong enough to produce self-sustained oscillations.
Experimental study on the characteristics of swirl effervescent atomizer
ZHAO Fang , XU Bingbing etc.
 doi: 10.11729/syltlx20210026
[Abstract](108) [FullText HTML](31) [PDF 6680KB](8)
Abstract:
Compared with the conventional pressure atomization and pneumatic atomization, effervescent atomization has the advantages of high efficiency, economy and environmental protection, which has attracted the attention of various fields. In this paper, a series of experiments were carried out on a variable nozzle internal swirling effervescent atomizer, and the effects of the working parameters, hole structure and mesh number on the flow and spray characteristics were discussed. The results show that flow characteristics of the atomizer with different hole structures are basically the same. The change of the air-liquid ratio results in the change of the liquid mass flow rate under the same working pressure. Flow characteristics are not affected by the cutting screen, while the addition of the cutting screen induces 3%–7% attenuation of the spay mass flow rate of under the same working condition, and the smaller the cutting screen aperture is, the greater the reduction of the spray mass flow rate is. The distribution of spray particles presents a single peak structure, and the median mean diameter of the spray decreases with the increase of the working pressure or air-liquid ratio. Under the same spray energy consumption, the special-shaped hole structure is more helpful to improve the spray performance. The cutting screen is beneficial to the spray performance, but the choice of the mesh aperture should be made based on the atomizer structure, the working pressure and other comprehensive judgment; in addition, the addition of the cutting screen reduces the axial velocity of the spray mainstream to a great extent.
Experimental study on drag reduction characteristics of biopolysaccharide solution
MENG Fanzhe , Qin Liping etc.
 doi: 10.11729/syltlx20210089
[Abstract](1520) [FullText HTML](58) [PDF 6347KB](17)
Abstract:
In order to obtain the underwater drag reduction performance of the biopolysac-charide solution, the drag reduction characteristics of four biopolysaccharide solutions of guar gum, xanthan gum, tragacanth gum and locust bean gum were tested in the gravity circulating water tank experimental system. The influence law of the injection rate, Reynolds number and injection mass fraction on the drag reduction is shown. The results show that the four biopoly-saccharide solutions have significant spray drag reduction effects, and the locust bean gum solution has the highest drag reduction rate(14.3%). At a constant Reynolds number, with the increase of the injection rate, the drag reduction rate of each polysaccharide solution increases significantly, and shows different trends after reaching the peak value of drag reduction. The drag reduction effect of the polysaccharide solution is better when the Reynolds number is small (<2.0×104). With the increase of the Reynolds number, the drag reduction law of the polysac-charide solution shows differentiation. Excessive injection mass fraction would reduce the drag reduction effect of the polysaccharide solution, and increasing Reynolds number would cause the phenomenon of “peak shift” with the increase of the mass fraction. By introducing relative injection mass fraction, the effects of the injection rate, Reynolds number and injection mass fraction on drag reduction are coupled with each other. With the increase of relative injection mass fraction, the drag reduction rate of each polysaccharide solution increases first and then decreases. Finally, based on the injection spray mass fraction, the drag reduction law of the polysaccharide solution was explained preliminarily.
Experimental study on flow control of asymmetric vortex over the leeward region of the head of the slender body by sliding discharge plasma actuation
JIN Yuanzhong , ZHENG Borui etc.
 doi: 10.11729/syltlx20210101
[Abstract](50) [FullText HTML](39) [PDF 7121KB](2)
Abstract:
When the aircraft flies at a high angle of attack, the flow field on the leeward surface of the slender body evolves in a complicated manner, and asymmetric vortices appear, generating random lateral forces, which greatly affect the maneuverability and agility of the aircraft. In order to solve this problem, a sliding discharge plasma actuator with an along-stream layout was used to conduct wind tunnel experiments on a slender body model, combined with pressure measurement and particle image velocimetry(PIV). The experimental results show that the actuation voltage of 10 kV is the threshold voltage at which the flow control starts to take effect. When the velocity of the incoming flow is 10 m/s(Re=0.8×105), the angle of attack is 45°, and the actuation voltage is 16 kV, the best flow control effect can be achieved at the normalized pulse frequency of 1.96, the lateral force coefficient can be reduced by 83.48%. However, as the flow velocity increases, the flow control effect becomes weaker gradually and is expected to disappear at 26 m/s.
A dual-junction thermocouple for flight test and its measurement error analysis
SHA Xinguo , WEN Shuai etc.
 doi: 10.11729/syltlx20210035
[Abstract](86) [FullText HTML](17) [PDF 6045KB](13)
Abstract:
The flight test needs fast response and small transducer for heat flux measurement. The dual-junction thermocouple, which is characterized by fast response, small size and abundant measured information, is one of the best solutions for the temperature and heat flux measurement in the flight test. The principle, structure and measurement method of the dual-junction thermocouple are studied, and dual-junction thermocouples are used in a flight test for the model surface temperature measurement. The model front-surface and back-surface temperatures were measured simultaneously by the dual-junction thermocouples, and it is found that the measured back-surface temperature has a greater error. The response time of the back-surface measurement point is much longer than that of the front-surface measurement point, which is affected by the junction size and the insulating coating between the junction point and the model surface. At present there is still a lack of the corresponding heat flux estimation method for the dual-junction thermocouple.
Optimization analysis of modified axial force element of sting balance
MIN Fu , XIE Zhendong etc.
 doi: 10.11729/syltlx20210083
[Abstract](123) [FullText HTML](39) [PDF 6441KB](7)
Abstract:
Aiming at the problem that the measuring of axial force is greatly disturbed by the normal force, a modified axial force element of sting balance is proposed. By means of theoretical analysis and finite element simulation, the deformation of axial force element under axial force and normal force is obtained. Meanwhile, mechanical analysis has been carried out to get the characteristics and reasons of the deformation of the measuring beam under normal force. The deflection angle between measuring beams and main beams of the modified structure is specific, and it is not 90°, which is obtained by linear fitting between the ratio of the interference of normal force on axial force to the output of axial force and the deflection angle. Simulation result of the modified structure shows that the axial force output is only reduced by 2.77%, moreover, the interference of normal force is reduced by 99.32%, compared to the conventional axial force element. The modified axial force element can obviously reduce normal force interference on normal force, so it can be used for wind tunnel aerodynamic test with large lift-to-drag ratio requirement.
Research on fluid-thermal coupling simulation of water-cooled calorimeter and experimental analysis
ZHU Xinxin , LI Zeyu etc.
 doi: 10.11729/syltlx20210011
[Abstract](295) [FullText HTML](35) [PDF 6671KB](4)
Abstract:
A kind of spherical water-cooled calorimeter including the ball crown calorific body and the heat shield is developed. The fluid-thermal coupling model of the calorific body and test water is established. The water temperature distribution characteristics in the waterway and the influence of water temperature on the heat flux measurement result are analyzed based on the model and heat flux calibration test. The results show that the closer the water in the waterway is to the heated surface, the higher the water temperature is and the greater the radial temperature gradient is. The smaller the water mass flow rate is, the greater the radial and axial temperature gradients are. So the thermocouple should be kept away from the heated surface and closer to the central axis of the waterway when the water-cooled calorimeter is designed. And the water-cooled calorimeter should be calibrated and the appropriate water mass flow rate range needs to be determined before use. Finally, the test results show that the spherical water-cooled calorimeter can be used to measure the stagnation point heat flux accurately in the long-term arc-heated wind tunnel test with multiple heat flux states.
Experimental study on flow separation control by flexible serrated trailing edge based on multi-scale coherent structure analysis
GONG Xu’an , ZHANG Xin etc.
 doi: 10.11729/syltlx20210041
[Abstract](200) [FullText HTML](71) [PDF 7140KB](18)
Abstract:
This article reports our recent experimental study of airfoil flow separation control by flexible serrated trailing edge. The experiments were conducted in a straight-type wind tunnel and a hot-wire anemometer was used to measure the velocity profile downstream of the two-dimensional airfoil. Multi-scale coherent structures within the separated shear layers are analyzed both in the time and frequency domains. The results show that the separation bubble thickness decreases by almost 5% of the chord length, the flexible serrated trailing edge vibrates and deforms adaptively and absorbs nearly 20% of the trailing edge shear layer’s energy, perturbation transmits to the leading edge shear layer, and thus the power spectral density decreases significantly in the lower and larger bandwidth to reduce the noise. The coherent structures’ frequency and amplitude also decrease notably, breaking and inhibiting the large vortex package’s transmission obviously in the separation bubble.
Experimental study on spreading and breaking mechanism of droplet impinging on low temperature wall at high speed
LEI Jilin , LI Jianwei etc.
 doi: 10.11729/syltlx20210066
[Abstract](270) [FullText HTML](76) [PDF 6779KB](16)
Abstract:
In order to study the dynamic behavior of a droplet impinging on a low-temperature wall, a visualization test was carried out on a single droplet impinging on a low-temperature wall (–30 ℃ - –10 ℃) with the Weber number between 533 and 1630 by the high-speed shadowing method. The experimental results show that prompt splash and corona splash occurs when the droplet impinges on the low temperature wall at the certain speed, and the splashing of secondary droplet is obvious. However, when the droplet impinges on the normal temperature wall at the same speed, there is no droplet breakage phenomenon. With the decrease of the wall temperature, the Weber number required for the droplets to smash into the wall decreases. When the wall temperature is –30 ℃, the critical Weber number of the droplet crashing into the wall decreases to about 650. When We < 650, even if the wall temperature is lower than –30 ℃, the droplets would not smash into the wall. When the droplet hits the normal temperature wall, the attached liquid film spreads out rapidly, and the larger the Weber number is, the greater the spread and retraction speed of the attached liquid film is, and the larger the spreading factor of the droplet is. This study provides a reference for the establishment of the impingement model of the droplet impinging on the low temperature wall surface.
contents
2022, 36(3).
Abstract(50) PDF(19)
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2022, 36(3): 0-1.
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Modern design of experiment and its development in aerodynamics
HAI Chunlong , HE Lei et al.
2022, 36(3): 1-10. doi: 10.11729/syltlx20220005
Abstract(104) HTML(40) PDF(43)
Abstract:
The scientific experimental design method can significantly improve the quality and efficiency of scientific research and industrial production. This paper introduces and summarizes the research progress of modern test design methods. Firstly, this paper summarizes the differences between OFAT(One Fact at A Time) method and MDOE(Modern Design Of Experiments) method in the wind tunnel test in three aspects: the test purpose, organization strategy and test results, and analyzes the advantages of MDOE method. Secondly, it summarizes the status quo of the MDOE method in three aspects: the experimental design, model establish-ment and result analysis. Then we demonstrate the experimental design method with standard functions and aerodynamic examples. Finally, some key scientific problems and future research directions are discussed.
Research on intelligent optimal design method of wind tunnel test scheme
JIANG Jinjun , ZHOU Xuanchi et al.
2022, 36(3): 11-19. doi: 10.11729/syltlx20210155
Abstract(104) HTML(16) PDF(39)
Abstract:
Advanced aircraft research requires rapid acquisition of correct-key data on the aerodynamic shape. The development of our country's aerospace equipment has gradually entered a stage of independent innovation. The exploration, innovation, and optimization of the aerodyna-mic design for a new generation of aircraft need to be supported by matching wind tunnel test capabilities. The development trend of high-performance and high-precision advanced aircraft has put forward higher requirements on the “quantity” and “quality” of wind tunnel test data, which means the design of traditional wind tunnel test schemes and data analysis modes have become increasingly unsatisfactory. It is necessary to make breakthroughs in wind tunnel test design and test data analysis technology. Based on aircraft ground test analysis, this paper uses the support vector machine(SVM) to model and analyze the test data, develop wind tunnel test plan optimization, design methods and test data intelligent analysis methods, and explore the new internal correlation between the aerodynamic data and aircraft geometric parameters. Building a wind tunnel test auxiliary design and analysis system to improve the efficiency of wind tunnel test and the accuracy of test data provides technical support for the aerodynamic design of high-performance aircraft.
Using modern design of experiments method for hypersonic wind tunnel test
YOU Wenjia , WANG Huijie et al.
2022, 36(3): 20-32. doi: 10.11729/syltlx20210179
Abstract(63) HTML(16) PDF(26)
Abstract:
Modern Design of Experiments (MDOE) is an important technical approach to improve wind tunnel test efficiency. Although the modern design of experiment method based on Latin Hypercube Sampling has high theoretical efficiency, the practical efficiency of the random sampling points designed by it decreases significantly when the automatic attitude control system of the wind tunnel model is coordinated. In this paper, a modern design of experiment method based on the Stratified Latin Hypercube design is proposed to meet the requirements of the multi-variable wind tunnel test design in the automatic attitude control system. It is applied to the two-variable test and three-variable test design of the 6 Mach number wind tunnel model. The results which were compared with the One Factor at A Time (OFAT) method show that MDOE method only needs about 20% of the sample size of OFAT method in the two-variable test and only needs about 30% of the sample size of OFAT method in the three-variable test. Compared with the classical Latin Hypercube method, the Stratified Latin Hypercube method developed in this paper combined with the existing wind tunnel test equipment can effectively reduce the change of test runs, improve the test efficiency and shorten the test period.
Investigation on artificial intelligence for the prediction of aeroacoustic performances and controlling parameters optimization of aircraft
WU Junqiang , YANG Dangguo et al.
2022, 36(3): 33-43. doi: 10.11729/syltlx20210073
Abstract(92) HTML(37) PDF(26)
Abstract:
Accurate aerodynamic characteristic data under different conditions is the prerequisite and fundamental guarantee for the fast design of a flight vehicle, the improvement of a control system, the evaluation of performances and performance appraisal. The cross synthesis between the machine learning technology (ML) based on deep neural network (DNN) and fluid mechanics is developing fast and has achieved remarkable progresses in the modification of turbulence models, modeling of systems, prediction of the aerodynamic and aeroacoustic characteristics, optimization of control parameters and reconstruction of the flow field. To effectively apply the powerful representative capability of DNN, according to the demand of intelligent optimization and design of weapon bays, this paper first established a database of aerodynamic loads for flows past cavities and then built deep forward neural network model for the prediction of aerodynamic loads. To enhance the robustness of the model, random search and Bayesian optimization are introduced during the training of the model. Numerical results show that the trained DNN model is able to predict the aerodynamic loads and aeroacoustic characteristics accurately and efficiently, which provides a useful tool for the prediction and control of the aeroacoustic characteristics of the cavity.
Predictive analysis of flow control in high-speed complex flow field based on machine learning
YU Baiyang , LYU Hongqiang et al.
2022, 36(3): 44-54. doi: 10.11729/syltlx20210168
Abstract(47) HTML(8) PDF(21)
Abstract:
The flow control actuator is the core of the active flow control technology. The design level and performance of actuator directly determine the application direction and effect of active flow control. In order to obtain the action law of the flow control actuator, a large number of experiments are needed to study the influence of excitation parameters on control effect parameters, and the experimental cost is large. In this paper, the experimental data of jet shock control in reverse plasma synthesis are used, and the Gaussian process regression model in machine learning is used to obtain the mapping law from the actuator parameters (head cone diameter, cavity volume, discharge capacitance and outlet diameter) to the control effect parameters (maximum out of body distance). We compare the prediction effects of Gaussian process regression under various kernel functions, and analyze the influence of actuator parameters on control effect parameters by using the characteristic importance analysis method. The results show that for this small sample problem, Gaussian process regression with the quadratic polynomial kernel function Poly2 obtains the highest accuracy; in characteristic importance analysis, the head cone diameter has the greatest influence on the maximum separation distance, followed by discharge capacitance and cavity volume. The influence of these two parameters is similar, and the influence of the outlet diameter is the least. The work of this paper can provide some guidance for the setting of various parameters of the actuator in the flow control experiment of the high-speed complex flow field.
Deep reinforcement learning for the control of airfoil flow separation
YAO Zhangyi , SHI Zhiwei et al.
2022, 36(3): 55-64. doi: 10.11729/syltlx20210085
Abstract(35) HTML(17) PDF(15)
Abstract:
A jet closed-loop control system based on Deep Reinforcement Learning (DRL) was built, and an experimental study was carried out on the separation flow control at high angles of attack on the NACA0012 airfoil. The airfoil chord length is 200 mm and the wind speed was 10 m/s. The Reynolds number was 1.36×105 based on the chord length. The jet actuator was arranged on the upper surface of the airfoil and the solenoid valve was used for stepless control. The pressure coefficient of the airfoil surface and the action output of the agent itself were taken as the observation of the agent. The pressure coefficient of the trailing edge of the airfoil was used as the reward function to train the agent. Our results showed that the trained agent successfully suppresses the flow separation at high angles of attack and the cost-effectiveness ratio is reduced by 50% compared with steady blowing. At the same time, the agent could also stabilize the pressure coefficient of the trailing edge near the target value. The state input and the change of the reward function also have different effects on the final training effect.
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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](208) [PDF 6594KB](25)
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](199) [FullText HTML](54) [PDF 10428KB](4)
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。
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](222) [PDF 5952KB](11)
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。
Review of research on the receptivity of hypersonic boundary layer
Jiang Xianyang, Li Cunbiao
2017, 31(2): 1-11.   doi: 10.11729/syltlx20160129
[Abstract](277) [FullText HTML](103) [PDF 7434KB](28)
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](210) [PDF 6603KB](10)
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](158) [PDF 4386KB](9)
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.
Study of micro flow visualization with nuclear magnetic resonance in core
Di Qingfeng, Hua Shuai, Gu Chunyuan, Ye Feng, Pang Dongshan, Jiang Fan, Yang Peiqiang
2016, 30(3): 98-103.   doi: 10.11729/syltlx20150107
[Abstract](103) [PDF 4151KB](0)
摘要:
岩心微流动可视化是研究化学驱油微观机理的一项重要流体实验新方法,重点介绍采用低场核磁共振成像技术研究天然岩心中流体分布可视化的新进展。提出和分析了国产低场核磁共振成像岩心驱替装置面临的图像不清、材料干扰等问题,通过合理选材、优化参数,从硬件和软件2方面进行了改进与优化,消除了干扰因素。开展了天然岩心的驱替实验,采集了油水的实时 NMR信号与 MRI 成像信号,以及不同驱替阶段油水的 NMR-T2谱,得到分辨率较高的油水分布图像。结果显示残余油随着驱替PV数的增加而减少,具有初期减少明显而后趋缓的特点,并发现岩心中存在端部油残滞现象,其范围距端部4mm左右。研究了通过获得的油水分布图像计算含油饱和度的方法,其结果与传统方法一致,误差在10%以内,这也说明了油水分布图像的可靠性。这不仅为计算饱和度提供了一种新方法,而且该方法的另一个优势是可以分析任意局部位置的油水饱和度。研究结果表明,在研究岩心微流动过程中流体分布的可视化方面,核磁共振成像技术是值得深入研究的新方法。
Simultaneous OH and CH2O PLIF imaging of flame structures
Zhu Jiajian, Zhao Guoyan, Long Tiehan, Sun Mingbo, Li Qing, Liang Jianhan
2016, 30(5): 55-60.   doi: 10.11729/syltlx20160026
[Abstract](194) [FullText HTML](83) [PDF 7981KB](5)
摘要:
OH和CH2O平面激光诱导荧光(PLIF)同时成像技术在研究火焰结构和燃烧反应中间产物二维分布等方面能够发挥重要作用。OH的分布被用来表征火焰反应区的结构,而CH2O的分布则被用来显示火焰预热区的分布。利用OH和CH2O PLIF同时成像技术研究了甲烷/空气部分预混火焰的结构。从实验系统、光路调节、时序同步、OH A-X(1,0)扫谱、数据采集和处理等方面讨论了PLIF同时成像技术的实验方法。实验结果表明,OH和CH2O PLIF同时成像能够分别呈现甲烷/空气部分预混火焰反应区和预热区不同形状的瞬时结构;由于反应区在相邻位置的结合,在火焰中能够局部生成新的分裂的预热区。
Advances influidic thrust vectoring technique research
Xiao Zhongyun, Jiang Xiong, Mou Bin, Chen Zuobin
2017, 31(4): 8-15.   doi: 10.11729/syltlx20160207
[Abstract](198) [FullText HTML](68) [PDF 5274KB](10)
摘要:
流体推力矢量技术不采用机械偏转,以流动控制方式实现推力转向,有望成为一种更加高效的推力矢量控制方法。目前实现流体推力矢量的主要方法有激波矢量法、双喉道方法、逆流控制方法和同向流方法等,对以上方法选择具有共性的计算与试验数据,对喷管的推力矢量效率、推力损失和流量系数进行了对比分析。结果表明激波矢量方法、双喉道方法和逆流方法能够在大落压比范围内(NPR=1.89~10)实现推力矢量控制,并且具有俯仰/偏航耦合甚至多轴控制的潜力。相比激波矢量法和逆流方法,双喉道和同向流方法在减少推力损失和提高矢量效率上占有优势,不足之处是双喉道方法对喉道进行控制限制了流量系数,而同向流方法的适用落压比范围受到严重限制。为寻求更加高效的矢量喷管技术,国内外相继发展了多种新概念流体推力矢量方法,对每种方法的控制原理、潜在优势和存在的问题挑战进行了探讨,新方法着眼于从喷流出口下游进行控制,对主流的干扰很小,值得深入研究,同时也为流体推力矢量的下一步研究方向提供了借鉴参考。
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](154) [FullText HTML](85) [PDF 9648KB](12)
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](2232) [FullText HTML](121) [PDF 8779KB](121)
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.
POD analysis of the dynamic structures of a low swirl number precessing jet
FU Hao, HE Chuangxin, LIU Yingzheng
2021, 35(4): 1-9.   doi: 10.11729/syltlx20210006
[Abstract](524) [FullText HTML](180) [PDF 7588KB](180)
Abstract:
The flow field of a low swirl number precessing jet at Reynolds number Re = 4.5×104 is measured using particle image velocimetry (PIV) and the dynamics of the large-scale flow structures are examined further using the proper orthogonal decomposition(POD) analysis. The spatial modes obtained by POD and the fluctuating velocity field obtained by POD reconstruction at three swirl numbers, i.e., S = 0, 0.26 and 0.41, are compared and analyzed. The POD results show that the precession induces an alternating flow, switching between outflow from one side of the chamber along the chamber wall and inflow from another side. When the precession occurs, the vortex structures in the upstream shear layers have not broken down completely. They will develop downstream until approaching the starting point of the precession and then deflect with the mainstream. However, the large-scale structures in the downstream shear layers are completely destroyed. As the swirl number increases, the region affected by the precession moves upstream, and the orderly vortex structures in the shear layers break down.
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