实验流体力学

An overview of supercooled large droplets icing condition simulation capability in icing wind tunnels

Fu Cheng, Song Wenping, Peng Qiang, Liao Daxiong, Wang Chao

2017, 31(4): 1-7. doi: 10.11729/syltlx20160118

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Abstract:
The icing wind tunnel is the most important ground facility in the research of ice accretion tests and the ice anti/protection devices design of airplanes. With the increasing importance of the supercooled large droplets ice accretions on the airplane surface and the development of the SLD airworthiness, the SLD icing condition simulation capability need to be developed in the icing wind tunnel. This paper presents the analysis results of the SLD icing condition in CFR14-25 Appendix O and the requirements of the SLD condition simulation in the icing wind tunnel. The developing status and the key problems of SLD icing condition simulation capabilities in several icing wind tunnels, such as IRT and CIRA-IWT are also presented. The three main key problems in the development of the SLD icing condition capability in the icing wind tunnel are the generation of large water droplets and it's turbulent mixing characteristics with the cloud in wind tunnel, the supercool process of large drops and the drop spectra accurate measurement in wide bands. The development roadmap and the key technology solution method of SLD icing condition simulation capability of icing wind tunnel of CARDC are presented in the end of this paper.

Advances influidic thrust vectoring technique research

Xiao Zhongyun, Jiang Xiong, Mou Bin, Chen Zuobin

2017, 31(4): 8-15. doi: 10.11729/syltlx20160207

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Abstract:
In contrast to the mechanical deflecting nozzle, the fluidic thrust vectoring control hires flow control methods to realize the jet vectoring, which is expected to be a more efficient way to manipulate the thrust direction. Among the main fluidic vectoring control methods, including shock vectoring control(SVC), dual throat nozzle(DTN), counter-flow(CC) and co-flow control, performance parameters such as the thrust vectoring efficiency, the thrust ratio and the discharge coefficient are compared based on published experimental and computational data. It shows that SVC, DTN and CC methods produce thrust vectoring in a wide range of Nozzle Pressure Ratio(NPR) from 1.8 to 10, and are extendable to pitch/yaw control or multi-axis control. Comparatively, DTN and co-flow control are superior to SVC and CC in the thrust loss and thrust vectoring efficiency, yet DTN is disadvantageous in the discharge coefficient as a consequence of throat injection, and the working range of co-flow method is highly limited. In pursuit of highly efficient control, some new methods of jet vectoring are introduced, and the principles, potential advantages and challenges of each method are discussed. These methods adopt after-deck-flow control and introduce little disturbance to the main jet, which are desirable for the thrust vectoring control. Such methods show promising prospects and the related experience should be drawn on for further studies.

Measuring DLVO force and surface potential based on AFM colloidal probe technique at liquid-solid interfaces

Tian Weifang, Zheng Xu, Li Zhanhua, Xu Zheng

2017, 31(4): 16-21. doi: 10.11729/syltlx20160163

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Abstract:
Surface potential is an important parameter of the fluid flow in microfluidics. This study develops a method to measure the surface potential and surface charge density based on the DLVO force obtained by colloidal probe technique using atomic force microscope (AFM). A novel procedure of colloidal probe fabrication is proposed, and then a cantilever-to-cantilever calibration method is used to determine the spring constant of the colloidal probe. We thus measure DLVO forces and surface potentials of silicon, silica and silicon nitride substrates, in 0.1 mM to 1 mM NaCl solutions respectively. The results show that our approach could well measure the DLVO forces at the liquid-solid interfaces, which is especially sensitive to the exponential variation of the electrostatic force. The surface potential, the surface charge density and other important parameters can be obtained via fitting the force curves. Additionally, the variation of surface potentials at different silicon-based surfaces indicates that the density of silane groups plays a dominant role on the surface potential. Thus it is possible to effectively control the surface potential by changing the silane density of the silicon-based materials. The findings could be valuable to regulating electro kinetic flow intensity in microfluidic chips.

Experiment study of propulsion-induced flow on aircraft aerodynamics

Zhang Chao, Zhu Jihong, Wu Linfeng, Li Huanyu, Li Chunwen

2017, 31(4): 22-27, 33. doi: 10.11729/syltlx20160154

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Abstract:
The characteristics of aircraft aerodynamic are the fundamental characteristics of aircraft. The influence of the propulsion-induced flow on the aerodynamic force is directly related to the accuracy of the aerodynamic modeling, the flight quality and the flight safety. A real turbojet engine is installed in a scaled-down aircraft model, and a more realistic static force measurement test is conducted under the different engine thrust force, air flow velocity and direction conditions. The results show that the influence of the propulsion-induced flow is mainly reflected in the axial force, the normal force and the pitching moment. The greater the engine thrust is, the more obvious the propulsion-induced effect is. And the maximum increment value of the normal force and the pitching moment appears with an angle of attack larger than the stall angle of attack. And the sideslip angle, wind speed (small range), as well as the control surfaces deflection caused by the aerodynamic increment is mainly manifested in the stall angle of attack. Therefore, the impact of propulsion-induced effect must be considered in the high angle of attack maneuver study.

Laser absorption spectroscopy diagnostics in the arc-heater of an arcjet facility

Zeng Hui, Chen Lianzhong, Lin Xin, Ou Dongbin, Dong Yonghui

2017, 31(4): 28-33. doi: 10.11729/syltlx20160179

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Abstract:
Gas temperature and species number density are the key parameters to quantitatively assess the arc-heated wind tunnel operation and flow quality. Conventional techniques meet great challenge in high enthalpy flow diagnostics for arc-heated facilities under prolonged operation at high temperatures. Based on the local thermodynamic equilibrium plasma assumption, this paper presents in-situ diagnostics for the dissociated air (＞5000K) in the arc heater by using laser absorption spectroscopy of atomic oxygen at the wavelength of 777.19nm. The gas temperature and the number density of atomic oxygen are measured under two operation conditions of H₀=15.8MJ/kg and 17.4MJ/kg, respectively. The average temperatures are 5843K and 6047K, corresponding to 5950K and 6335K from charts for high temperature equilibrium flow properties of air. The number density of atomic oxygen is within (1.1~1.2)×10¹⁸cm^-3 and is in consistency with the calculation via NASA-CEA program, while the number density of atomic oxygen (⁵S₂⁰) is within (1.0~1.5)×10¹⁰cm^-3. This work demonstrates that the laser absorption spectroscopy is applicable for high enthalpy flow diagnostics in the arc-heated wind tunnel as a new technique.

Design of civil aircraft's static source aerodynamic layout

Yang Hui, Yang Shipu, Huang Di, Sun Yifeng

2017, 31(4): 34-38, 58. doi: 10.11729/syltlx20160109

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Abstract:
Civil aircraft obtains the flight height, speed, etc. by the air data computer with the measured static pressure, total pressure and other basic parameters as input. Therefore, the flight safety strongly depends on the accuracy of the static pressure measurement which is related to the aerodynamic layout of the static ports. For subsonic civil aircrafts, the pressures measured by static ports are mainly affected by the Mach number, angle of attack(AOA) and the configuration of the aircraft. Based on CFD results, the positions of static ports are determined by the mean square deviation method. The measurement characteristics of static ports and the disturbances on measurement due to the flap/slat, spoiler, landing gear and ground effect which are essential inputs for the static source error correction (SSEC) were obtained by wind tunnel tests.

Blade tip vortex measurements of a hovering rotor

Liu Ping'an, Lin Yongfeng, Chen Yaofeng, Yuan Mingchuan

2017, 31(4): 39-44. doi: 10.11729/syltlx20160186

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Abstract:
In order to investigate the structure of blade tip vortices, Panicle Image Velocimetry (PIV) measurements were conducted on tip vortices trailing from the rotor with slotted blade to quantify the swirl velocity, core radius and vorticity profile at a fixed wake angle of 145 degree. The influence of the PIV image analysis parameters, e.g. sampling window size, on the vortex structure parameters has been investigated. To mitigate the effects of vortex wander, a scheme to align the velocity fields based on the locations where the velocity minimum appears prior to averaging was developed. Compared to simple average, the conditional average method obtains more accurate parameters of the vortex.

The seawater surface tension coefficient representation with different salinities

Zhang Zhiyou, Jin Liang'an, Yuan Zhijiang, He Shengyang

2017, 31(4): 45-50. doi: 10.11729/syltlx20160164

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Abstract:
To study the seawater surface tension coefficient representation with different salinities and to simplify the test methods, a practical model for the bubble departure volume and the departure instantaneous velocity is built by analyzing the forces experienced by the bubble in the seawater. The underwater gas emission experimental platform is constructed. It uses the normal pressure air and six kinds of salinity seawater as the experiment's gaseous phase and liquid phase. And the bubble motions are categorized as slow motion with low Reynolds number and fast motion with high Reynolds number. Experiments with both bubble motions are conducted. The high-speed photography technology is used to record the bubble motion, and the filmed pictures are analyzed by the MATLAB program, so as to obtain the bubble departure volume and the departure instantaneous velocity. Substituting the experimental data into models, the seawater surface tension coefficient representation with different salinities can be acquired. The result shows that, under the non jet generation and flotation condition, the bubble is of small radius and has slow movement with low Reynolds number. The simulation results are in consistency with the measurement with high credibility and low divergence. The error is less than 2%.

A dynamic calibration method for a dynamometric system in impulse combustion facilities

Wu Long, Wang Feng, Le Jialing

2017, 31(4): 51-58. doi: 10.11729/syltlx20160158

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Abstract:
A new dynamic calibration method for a dynamometric system in impulse combustion facilities is proposed. The calibration involved uses an instrumented impact hammer to apply individual calibration forces in different directions at different positions on a face of the model and calculates the unit impulse response function (UIRF) of the face from input loads and output strains. UIRFs of different faces are weighted to obtain the UIRF of the dynamometric system and the weighting coefficients are determined by the pressure on each face under the experimental condition. By parameterization, the problem is converted into a parameter optimization problem to solve the UIRF. Using a genetic algorithm to obtain the approximation of the global optimal solution of the parameters and setting it as the initial value of a simplex algorithm, the exact solution is obtained by the simplex algorithm then. ANSYS simulation of the dynamic calibration is presented. Input loads and output strains are recorded and noises are added to the output strains to simulate the actual experimental situation. The simulation validates the accuracy and feasibility of the dynamic calibration method.

Study on technology of using flaky hinge moment balance for high-aspect-ratio wings based on external electric bridge correction method

Jia Wei, Liu Weiliang, Zhao Zhongliang, Miao Lei, Xie Bin, Mi Peng, Yang Hongsheng, Wang Shumin, Chen Zhu

2017, 31(4): 59-63. doi: 10.11729/syltlx20160107

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Abstract:
In application, the precision and accuracy of the traditional flaky hinge moment balance for the high-aspect-ratio wings are not high enough. The problem is caused by the additional interference signal resulted from the aerofoil transformation. Aiming at enhancing the hinge moment wind tunnel test data's precision and accuracy for the high-aspect-ratio plane, the External Electric Bridge Correction Method (EEBCM) is explored. It is a new type of signal correction method using a set of signals to correct other signals, and its operational principle, steps and workflow are expounded in detail. Taking a wind tunnel test as an example:the external bridge is arranged on the wing, and the measurement results are compared with those without correction. The comparison shows that without the signal correction the balance measurement error is up to 54%, after the signal correction the measurement error is reduced to 6%, and the balance measurement accuracy has been improved. The present study provides a new idea for the application of the hinge moment balance to the high aspect ratio wings.

General data processing system for multiple wind tunnels

Deng Xiaoman, Fan Jinlei, Yu Li, Li Chunyan, He Fu

2017, 31(4): 64-70. doi: 10.11729/syltlx20170051

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Abstract:
In order to improve the standardization and efficiency of the wind tunnel test data system and improve the reliability and automation of data processing and analysis, a general test data processing system is established for multiple wind tunnels and a variety of test types. On the basis of standardized data processing methodology, processes, symbols and formats, the general system uses the service-oriented software architecture, heterogeneous data storage management, the user defined formula expansion based on dynamic compilation, and the visualized file format editing based on metadata and template. Key problems of the general system are solved, such as the system architecture, processing methods and process control, data flow and file output, etc. In the last three years, 71.2% of test data of 6 wind tunnels in the High Speed Institute of China Aerodynamics Research and Development Center were processed by the general system, covered test types including single and multiple balances forces and moments measurement, pressure measurement, venting measurement, mixed forces and pressure measurement, jet test and some special tests. With the characteristics of being universal, efficient, and open, the general system is a data processing and management solution that worth promoting.

Thermodynamics model updating of cryogenic wind tunnel diffuser based on response surface method

Ma Yueyin, Nie Xutao, Chen Wanhua, Yao Chengwei, Zhang Wei

2017, 31(4): 71-78. doi: 10.11729/syltlx20160133

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Abstract:
A great amount of liquid nitrogen and power is consumed to run the cryogenic wind tunnel. The temperature variation of the wind tunnel may cause excessive thermal deformation and stress, which can have a significant influence on the wind tunnel safety. Thus, it is indispensable to develop the reliable thermodynamic model of the cryogenic wind tunnel for evaluating the safety, performance and economy efficiency. In this paper the cryogenic wind tunnel diffuser is studied and its thermodynamic model is established based on the finite elements method. Moreover, the response surface method is adopted to correct some model parameters for purposes of improving the consistency between the finite elements model and the actual model. Firstly, according to the differences between the test data and simulation results the internal surface convective heat transfer coefficients of the plenum tapered shell are chosen as the parameters that need to be corrected. Secondly, the sample space of the finite elements thermal analysis is generated by using the central composite experiment design. Thirdly, the nonlinear regress analysis of the residual mean square is carried out in the sample space to establish the response surface model. Finally, the residual mean square sum of all monitor results is taken as the objective function and then the thermodynamic model is analyzed and optimized by means of the nonlinear multi-object optimization algorithm. The model verification results show that the updated thermodynamic model is highly consistent with the actual model and it is feasible to correct the thermodynamic model with the response surface method.

Experimental investigation on critical pressure ratio of hypersonic wind tunnel vacuum system

Chen Aiguo, Li Zhenqian, Qi Dawei, Long Zhengyi, Yang Yanguang

2017, 31(4): 79-83, 96. doi: 10.11729/syltlx20160115

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Abstract:
When the pressure in the vacuum container of the intermittent type hypersonic wind tunnel rises up to a certain extent, the flow field in the test section begins to destroied, and the static pressure in the test section would be unstable. The pressure in the vacuum container at the corresponding unstable point is called the critical pressure. The critical pressure would affect the vacuum system design of large-scale hypersonic wind tunnels (Ma ≥ 10). The experiment is carried out in the Φ0.3m hypersonic low density wind tunnel, where the Mach number is over 10. The pressures in the test section, the pitot tube, the diffuser and the vacuum container have been measured. The critical pressure ratio of Ma10, Ma12 and Ma16 is 0.34, 0.35 and 0.5 respectively. The wind tunnel flow field unsteady process from establishment to destruction is simulated by FASTRAN software. The calculation result is in agreement with experimental result. The investigation provides key data for the vacuum system design of similar larger hypersonic wind tunnels.

Research on method for evaluating the thermal protective performance of non-catalysis material in non-equilibrium flow

Yu Mingxing, Bai Shuxin, Xu Xiaoliang, Cao Zhanwei

2017, 31(4): 84-89. doi: 10.11729/syltlx20170084

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Abstract:
In this paper, an effective wind tunnel test method is presented for evaluating the thermal protective performance of the non-catalysis material. The method is proved to be reasonable by iterating the results between CFD simulation and the wind tunnel operating parameter, taking a typical CMC(ceramic matrix composite) wedge-edge specimen for example. The operating parameters of the arc tunnel was determined by comparing the simulation results of the non-catalysis and the full-catalysis assumption. The wind tunnel test results indicate that the test on the specimen was performed as expected, which may be helpful to solve the 'under-evaluating' problem for the non-catalysis material in the non-equilibrium flow.

Uncertainty assessment for aerodynamic test in Φ0.5m hypersonic wind tunnel

Liu Chunfeng, Xiong Lin

2017, 31(4): 90-96. doi: 10.11729/syltlx20160121

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Abstract:
Based on AGARD(AGARD-AR-304) and AIAA(AIAA S-071A-1995) of wind tunnel test uncertainty assessment, the standard is extended to the Φ0.5m hypersonic wind tunnel test. The specific procedure is:distinguish all the uncertainty sources according to the test process; estimate the uncertainty of independent variables, including the value of bias limit and precision limit; finally assess the uncertainty from dominance independent variables based on the standard, and assess the uncertainty from the attack angle using the linear interpolation. The result of a lifting model shows that the systematic errors are the major contributor to the uncertainty; the uncertainty results of C_N, C_A and C_m are notably different at different attack angles, while the relative uncertainty of C_m has the maximum value; the sensitivity analysis shows that the uncertainty from the balance and the total-pressure probe dominates the result.

2017 Vol. 31, No. 4