实验流体力学

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2022, 36(5)

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Abstract:

Ejector system design and performance test of Φ1.2 m hypersonic wind tunnel

MA Lichuan, WANG Tiejin, CUI Chun, HUANG Jingbo, SUN Yongtang, HUANG Bingxiu, SHI Yunjun

2022, 36(5): 1-7. doi: 10.11729/syltlx20210139

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Abstract:
Aiming at the problems such as high pressurization ratio, wide suction range and multi-stage parameter matching in large hypersonic wind tunnel, this paper carried out the design calculation and suction test of the multi-stage ejector system in Φ1.2 m hypersonic wind tunnel. Through single stage performance debugging and multistage combination performance debugging of the first, second and third stage ejector without wind tunnel main flow, the suction performance of three stage multi nozzle central ejector with different working parameters is obtained. The minimum static pressure in the test section is 660 Pa without the main flow. And the parameter matching principle of efficient operation of the multi-stage ejector is analyzed and summarized. The test results of the ejector coefficient with the main airflow in the wind tunnel are in good agreement with the theoretical calculation values, which verifies the feasibility of the aerodynamic design method for the multistage multi-nozzle ejector. The design results are reliable, which can provide technical reference for the design of the multistage ejector system in the hypersonic wind tunnel or other ground aerodynamic test equipment.

Prediction of icing wind tunnel temperature field with machine learning

ZHANG Xinghuan, ZHANG Pingtao, PENG Bo, YI Xian

2022, 36(5): 8-15. doi: 10.11729/syltlx20210196

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Abstract:
Icing wind tunnel is an important infrastructure for research on aircraft icing and anti-deicing in which refrigeration system realizes precise control of the airflow temperature in the wind tunnel by adjusting the suction pressure of the compressor unit. The suction pressure control and cooling methods affect the wind tunnel test efficiency. In this paper, aiming at accurate prediction of compressor suction pressure, the support vector regression （APSO–SVR） optimized by adaptive particle swarm algorithm is used to establish pressure prediction model to conduct pressure prediction and experimental research. In order to further improve the efficiency of icing wind tunnel testing, multi-layer perceptron （MLP） neural network is used to establish an analysis model to analyze the influence of test parameters on the cooling rate of wind tunnel. The results show that the average absolute percentage error （E_MAP） between the predicted and test value of the compressor suction pressure is less than 4%, and the mean square error （E_MS） is less than 0.003; the parameters affecting the wind tunnel cooling rate are mainly airflow density, test wind speed, compressor suction pressure and the initial temperature of the heat exchanger outlet. Among them, the compressor suction pressure has the most significant effect on it.

Research on key technologies of heat exchanger design for large-scale continuous high speed wind tunnel

ZHAO Bo, HUANG Zhilong, CHEN Jiming, LIAO Daxiong, PEI Haitao

2022, 36(5): 16-23. doi: 10.11729/syltlx20210080

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Abstract:
With the increase of the operation power and higher requirement on the fine measurement of the large-scale continuous high speed wind tunnel, higher performance of the wind tunnel heat exchanger is required, which is mainly reflected in the heat transfer and pressure loss performance, temperature field uniformity and flow field perturbation characteris-tics. Based on recent years' research, the key technologies and research results in the design of the large-scale continuous high speed wind tunnel heat exchanger are comprehensively discussed. Firstly, the required characteristics of the wind tunnel heat exchanger are analyzed, and the main factors affecting various performances are summarized. Then the high efficiency low-pressure loss design technology is introduced along with the temperature uniformity control technology and the airflow disturbance control technology. The principles of comprehensive trade-off of the heat transfer efficiency and pressure loss of the heat exchanger are presented. And the influences of the heat transfer core arrangement, cooling water flow and its inlet direction, cross section shape of the heat exchanger segment on the temperature field uniformity are discussed. Finally the flow disturbance characteristics downstream of the heat exchanger under different flow conditions and heat exchanger structures are analyzed.

Design and actualization of the variable density plane cascade wind tunnel

WEI Wei, MA Husheng, ZHOU Xiaogang, WU Junqiang, PENG Qiang, REN Zebin

2022, 36(5): 24-33. doi: 10.11729/syltlx20210175

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Abstract:
In order to meet the need of the variable Reynolds number plane cascade tests for the advanced turbofan engine, the variable density plane cascade wind tunnel was designed to change the subsonic, transonic and supersonic flow efficiently, adjust the Mach number （Ma） and Reynolds number （Re） independently, combine the compressor and turbine cascade tests and possess the ability of heat transfer or cooling experiments. The general design project of the wind tunnel was put forward, and the ejector, the flexible nozzle as well as the test chamber design problems were introduced in details. The results of the flow field debugging and the typical cascade tests were analysed. The research reveals that the design technologies of the components satisfy the main functions of the variable density plane cascade wind tunnel. The Reynolds number can be as low as 3.1×10⁵m^–1 so that the low Reynolds number experiments can be made easyly with the facility. The flow field debugging results satisfy the National military standard GJB 1179A—2012 of the specification for flow quality of high and low speed wind tunnels. It provides a key test platform for the study of the transonic, supersonic Mach number and low Reynolds number flow problems of the compressor and turbine cascades.

Research on test technology of civil aero-engine combustor

MENG Gang, HE Min, ZHANG Jingwei, CHEN Zhilong, QIN Hao, ZHENG Dan

2022, 36(5): 34-42. doi: 10.11729/syltlx20210177

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Abstract:
In recent years, the engines for large commercial airplane are being developed closely, and the tests for main components and the whole engine are being conducted massively in China. For the purpose of supporting the development of low-emission combustors, the paper introduces the typical R&D path of a civil engine combustor, and mainly focuses on the test technologies of single cup, multiple cups and full annular combustors, in which the main test subjects, test process, instrumentation, key points and common issues have been summarized. At the same time, by making a comparison of test pressure/temperature, instrumentation, test abundance and perspectiveness between China and western countries and by summarizing of Chinese civil combustor test technology developments, the paper gives reference to the domestic researchers in the fields of low-emission combustor research, test facility construction, measure-ment enhancement and gap filling.

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, YU Minghao, LIU Yuanpeng, ZHANG Qian, SUN Zhengzhong, YU Tao

2022, 36(5): 43-51. doi: 10.11729/syltlx20210101

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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, SUN Riming, ZHANG Zongbo, JI Feng

2022, 36(5): 52-56. doi: 10.11729/syltlx20210035

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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.

Research progress of hinge moment test technique in hypersonic wind tunnel

XIANG Liguang, SHU Haifeng, XU Xiaobin

2022, 36(5): 57-68. doi: 10.11729/syltlx20210087

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Abstract:
Compared with hinge moment tests in the low speed and high speed wind tunnel, the hypersonic wind tunnel hinge moment test has smaller model size, larger effect of temperature and gap interporosity flow, and larger test difficulty. The research on the hypersonic hinge moment test technique is to seek the method to solve these difficulties. Since the 11^th Five-Year Plan, relevant work have been done by Hypervelocity Aerodynamics Institute of China Aerodynamics Research and Development Center in Ф1 m Hypersonic Wind Tunnel. The design technology of the balance and test equipment based on the vertical axis, horizontal axis and other layout modes has been developed successively. The measures to reduce the temperature effect, the rudder deflection transformation method and the balance calibration method suitable for hypersonic wind tunnel test conditions were explored, and several rounds of verification tests were carried out. Experimental results show that the developed test method, test device, balance structure, rudder deflection transformation method, and balance calibration method can meet the requirements of aerodynamics measurement of the control rudder of different hypersonic flight vehicles. The temperature effect of the balance and the effect of the gapinterporosity flow can be reduced effectively by installing the heat insulation sleeve at both ends of the balance and using the electric bridge compensation. The test technology has been successfully applied to the measurement of aerodynamic characteristics of the rudder surface in Ф1 m Hypersonic Wind Tunnel with Mach number 4–8 and total temperature of 273–740 K, and the repeatability accuracy of the hinge moment is better than 1.50%.

Study on flow field characteristics of inert gas-air hybrid arc

DU Baihe, ZHANG Songhe, GE Qiang, WANG Maogang

2022, 36(5): 69-75. doi: 10.11729/syltlx20210052

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Abstract:
Adding a small mass flow rate of inert gas into the air arc flow field does not affect the performance evaluation of the thermal protection materials. In order to obtain the flow field characteristics of the inert gas-air hybrid arc, the flow field parameters of the supersonic nozzle exit were studied by controlling the arc current and inert gas mass flow rate in an arc heated wind tunnel. The experimental results show that the enthalpy and stagnation point heat flux of the helium-air hybrid arc are 6.07% and 1.02% higher than that of the air arc flow field respectively under the condition of helium mass ratio of 11.46%, total mass flow rate of 0.2 kg/s and arc current of 1300 A; the enthalpy and stagnation point pressure of the hybrid arc with inert gases such as neon, argon and krypton are lower than that of the air arc at the exit of the supersonic nozzle, and increase with the increase of mixed gas flow rate and arc current. The increase degree is related to the proportion of the added gas medium and total mass flow rate.

Optimization analysis of modified axial force element of sting balance

MIN Fu, XIE Zhendong, DAI Jinwen, PI Xingcai, YANG Yanguang

2022, 36(5): 76-82. doi: 10.11729/syltlx20210083

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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.

Numerical simulation and experimental test of unsteady flow field for oscillating vanes gust generator in high-speed wind tunnel

ZHANG Ying, LIU Nan

2022, 36(5): 83-89. doi: 10.11729/syltlx20210093

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Abstract:
Gust generator is the important equipment of the gust test system. In order to reduce the risk of development, a set of oscillating vanes gust generator suitable for 0.6 m continuous transonic wind tunnel was designed and processed. The self-developed ENSMB software was used to numerically simulate the unsteady flow field for the generator, and the formation mechanism and distribution characteristic of the disturbance velocity field downstream of the generator were analyzed. The research focused on the influence of the oscillating frequency and maximum oscillating amplitude of gust vanes on the gust velocity amplitude, and compared the results with the experimental data. The results show that the calculated results are in good agreement with that obtained by experiment. The gust velocity field downstream is caused by the vortex shedding from the vane, and changes periodically and sinusoidally with time. The gust velocity amplitude increases first with the increase of the maximum oscillating amplitude of gust vanes. When the maximum oscillating amplitude is 10°, the gust velocity amplitude reaches the maximum, and then there is no obvious change. This is probably due to the stall caused by the maximum oscillating amplitude increase. The frequency change only affects the frequency of the gust velocity, but has no obvious influence on the gust velocity amplitude.

Design and application of the dynamic stage separation device in hypersonic wind tunnel

HE Chao, SUN Peng, LIN Jingzhou, XU Xiaobin, CHEN Lei

2022, 36(5): 90-95. doi: 10.11729/syltlx20200119

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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 on spreading and breaking mechanism of droplet impinging on low temperature wall at high speed

LEI Jilin, LI Jianwei, LIU Yi, GOU Yao, LIU Yang, DENG Xiwen

2022, 36(5): 96-101. doi: 10.11729/syltlx20210066

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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 the normal temperature （22 ℃） and 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 aluminum plate decreases to about 480. When We < 480, 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 droplet spreads out rapidly, and the larger the Weber number is, the greater the spread and retraction speed of the droplet 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.

2022 Vol. 36, No. 5