实验流体力学

Shock interactions in near-axisymmetric internal contraction flows

Ji Junze, Li Zhufei, Zhang Enlai, Yang Jiming

2019, 33(5): 1-9. doi: 10.11729/syltlx20190046

Abstract(246) HTML (155) PDF(21)

Abstract:
The near-axisymmetric contraction flow in internal cones with different angles of attack is proposed to simplify the complicated three-dimensional shock interactions in a hypersonic inward-turning inlet. The interactions of the shock at near-axisymmetric contraction conditions are revealed efficiently using a combination of experiments in a shock tunnel and numerical simulations. The results show that the axisymmetric incident shock strengthens toward the central axis due to the convergence effect until a Mach disk is formed. It has been shown that the Mach reflection at the central axis is an inevitable phenomenon, which prevents the convergence and enhancement of the axisymmetric incident shock even for a small compression angle of the leading edge of the internal cone. However, when the incoming flow has an angle of attack, the flow field deviates slightly from the axisymmetric state and presents complex three-dimensional characteristics. The windward incident shock strengthens faster than the leeward incident shock along the flow direction. As a result, the shock interaction position on the symmetry plane deviates from the axis and the regular reflection can occur. The local pressure immediately downstream the reflection position for the regular reflection can reach a much higher level than that behind the Mach disk for the conditions where the Mach reflection occurs. Moreover, with the increase of the leading edge compression angle of the internal cone, the critical angle of attack for the appearance of the regular reflection on the symmetry plane also increases.

Self-ignition caused by an imploding arc-shaped shock wave and the subsequent propagation of combustion

Hou Zihao, Yang Jianting, Zhu Yujian, Yang Jiming

2019, 33(5): 10-17. doi: 10.11729/syltlx20190043

Abstract(107) HTML (101) PDF(5)

Abstract:
The self-ignition induced by an imploding arc-shaped shock wave and the subsequent propagation of the combustion waves are investigated by shock tube experiments and quasi-one-dimensional numerical simulations. A carefully designed transitional tube section is employed to smoothly transform the incident planar shock wave to an imploding arc-shaped shock wave. It is found that the non-uniform gradient environment behind the imploding shock consists of three different regions that are respectively produced by the shock wave propagation in the straight section, the transitional section and the wedge section. With the strengthening of the imploding shock wave, a mild chemical reaction zone with absence of shock waves breaks out at a spot behind the arc shock. The upstream front of the reaction zone moves faster than the Chapman-Jouguet (CJ) detonation speed in the very beginning, and the flow of the reaction products exhibits characteristics of a weak detonation wave. Further analysis indicates that the upstream reaction front is essentially a spontaneous reaction wave instead of a hydrodynamic wave and the moving speed of it is consistent with the reciprocal of the local ignition time gradient. The expandence speed of the reaction zone quickly drops below the CJ speed, accompanying with the emergence of shock waves and a shock-flame complex. The shock-flame complex accelerates and transits to a detonation wave, eventually. Under a certain circumstance and because of the unique induction time gradient environment, the spontaneous reaction wave front may overtake the detonation wave to become the new combustion front. Again, when the speed of the spontaneous wave front drops below the CJ detonation speed, a new detonation wave takes over. In this process, the original detonation wave degenerates to a shock wave propagating in the combustion products.

An analysis on typical influencing factors of wind tunnel experimental model of over-under TBCC inlet mode transition

Liu Yuan, Qian Zhansen, Xiang Xianhong

2019, 33(5): 18-27. doi: 10.11729/syltlx20190007

Abstract(216) HTML (99) PDF(18)

Abstract:
The aerodynamic performance of a typical over-under TBCC inlet mode transition model has been studied by wind tunnel experiments, and the CFD methods used have also been verified. In the present work, the influence of three typical factors on the experiment is studied by the CFD method, including the side gap, the leading edge bluntness and the forward step on the inner surface. The research results show that the gap between the splitter and the side plate leads to flow spillage between the high and low speed channels. When the gap width reaches 0.5 mm, the total pressure recovery coefficient of the high speed channel is increased by 2.13%, while the flow coefficient is improved by 2.27%. This already has an impact on the aerodynamic performance evaluation of the inlet so that the gap of the model plate should be less than 0.5 mm.The blunted radius of the leading edge has little influence on the aerodynamic performance of the inlet. For the general machining accuracy (0.3 mm), the inlet performance remains basically unchanged. For the general assembly accuracy (0.5 mm), the forward step has very little influence on the inlet flow coefficient, and the total pressure recovery coefficient of the inlet is decreased by 0.44%, which can satisfy the requirements of aerodynamic performance evaluation of the TBCC inlet.

Integrated design and experimental research for curved fore-body and 3D inward turning inlet

Zheng Xiaogang, Li Zhonglong, Li Yiqing, Zhang Xu, Zhu Chengxiang, You Yancheng

2019, 33(5): 28-35, 48. doi: 10.11729/syltlx20190019

Abstract(168) HTML (112) PDF(7)

Abstract:
An integrated design method for the curved fore-body and the 3D inward-turning inlet is proposed firstly. For the effect of the side-wall expansion angle, two models with different expansion angles are designed and constructed. Wind tunnel tests for them were carried out under the design condition Ma=6.0 and α=0°. The numerical and experimental results show that the new developed integration method is reasonable. The initial conical shock wave induced by the curved fore-body is able to match the cowl lip perfectly so that the spill flow from the cowl lip can be reduced effectively. The mass flow capture capacity of the integrated model can be improved by increasing of the expansion angle in the present work. However, the growth of the expansion angle can possibly depress the back-pressure characteristic of the integrated configuration. Therefore, a proper expansion angle should be selected to meet the overall requirement for the integrated model.

Experimental investigation on the characteristics of wingtip vortex at low Reynolds number

Xue Dong, Pan Chong, Yuan Xianshi, Liu Ruiqing

2019, 33(5): 36-41. doi: 10.11729/syltlx20180129

Abstract(200) HTML (96) PDF(15)

Abstract:
The characteristics of wingtip vortex mainly consist of the vortex core radius, the mean vorticity and the tangential velocity, etc., and the accurate measurements are essential for controlling the wing-tip vortex. In the present study, 2D particle image velocimetry was used to measure the velocity fields of the cross-section downstream the wake vortices in the water tunnel, and the measurement region covers the near and mid/far field where the wingtip vortex persists. Due to the effect of the unsteady motion on the accuracy of measurements, we adopted re-centered average method to extract the characteristics of the vortex pair from the velocity field, which improves the accuracy of statistical parameters. The results show that the vortex core radius and the peak vorticity increase and decrease with the stream-wise position with power law respectively; the unsteady amplitude decreases with angle of attack, which indicates that the resistance ability of the vortex pair to the disturbance grows with the vortex strength.

Experimental study of magnetohydrodynamic power generation system in arc heater

Ou Dongbin, Zeng Hui, Yang Guomin, Zhu Anwen, Liu Feibiao, Wang Zhu, Peng Yan, Liu Baolin

2019, 33(5): 42-48. doi: 10.11729/syltlx20180189

Abstract(422) HTML (232) PDF(63)

Abstract:
The high power electric propulsion and energy system is in urgent demand for the next generation space exploration. This paper presents ground-based tests on the high-temperature magnetohydrodynamic(MHD) power generation system by utilizing arc heater. The required temperature and pressure conditions for power generation are provided by the arcjet and the conductivity of the testing gas is improved by injecting the seeding cesium. Linear and disk MHD power generation is successfully carried out respectively:the maximum output power of the linear MHD power generator reaches 196 W under the test condition of 1 T magnetic-field intensity, and the maximum output power of the disc generator reaches 10.5 kW under the test condition of 7 T magnetic-field intensity. It demonstrates the prospect of the MHD power generation technology and lays foundations for the research of the higher power MHD generator and space application.

Measurements and data processing technology of freestream fluctuations in hypersonic wind tunnel

Yu Tao, Wang Junpeng, Liu Xianghong, Zhao Jiaquan, Wu Jie

2019, 33(5): 49-56. doi: 10.11729/syltlx20180142

Abstract(289) HTML (170) PDF(20)

Abstract:
Freestream fluctuation has a direct impact on the experiments carried out in hypersonic wind tunnels, due to effects such as hypersonic laminar/turbulent boundary-layer instability and transition. In order to obtain a deep insight into the mechanism in the hypersonic boundary layer instability, it is significant to measure and quantify the freestream disturbance in the hypersonic wind tunnel. Upon this work, we propose a novel approach for the disturbance modes characterization such that the hypersonic freestream can be measured by the hot-wire anemometer and the Pitot probe simultaneously. All the amplitudes of the disturbance modes, such as the entropy, vorticity and sound wave modes, are derived based on the small disturbance assumption by using the transfer function for the Pitot probe, which is obtained from direct numerical simulation. This novel approach for disturbance decomposition in hypersonic freestream has been applied in the Mach 6 Ludwieg tube wind tunnel at Technical University of Braunschweig in Germany. The experimental results show that this Ludwieg tube tunnel is a typical noise wind tunnel, in which the acoustic mode is up to 69% of the total disturbance mode, and the vortex mode and entropy mode account for about 15% respectively. This disturbance mode decomposition method sheds light on the freestream disturbance measurement in the hypersonic wind tunnel and provides valuable data for hypersonic wind tunnel experiments.

Study on artificial neural network modeling and wind tunnel test for the FADS system applied to the vehicle with sharp nosed fore-bodies

Wang Peng, Jin Xin

2019, 33(5): 57-63. doi: 10.11729/syltlx20180125

Abstract(273) HTML (176) PDF(14)

Abstract:
The solving model and its accuracy for the Flush Air Data Sensing (FADS) system applied to the vehicle with sharp nosed fore-bodies are studied. Firstly, the pressure ports configuration for sharp nosed fore-bodies is determined based on the theoretical model of the FADS system applied to the blunt fore-bodies. Secondly, a typical wind tunnel test for the FADS pressure ports is implemented, and CFD results and wind tunnel test are analyzed systematically. Finally, the solving model and algorithm are developed for the FADS system based on the Radial Basis Function (RBF) neural network modeling, and the neural network model solving accuracy for the FADS system is analyzed. The results show that, the solving accuracy of the RBF neural network model for the FADS system is high enough. The neural network outputs agree well with the wind tunnel test data, and the testing error distributions (absolute error distribution) for the angle of attack, angle of sideslip, free stream static pressure and Mach number are less than 0.1°, 0.1°, 50.0 Pa and 0.01, respectively. The results also present that the artificial neural network modeling for the FADS system can be further developed in the future.

Artificial icing tests of the helicopter anti-icing system

Ren Zhiyong, Li Zhipeng, Wang Junqi, Ma Dingfeng

2019, 33(5): 64-69. doi: 10.11729/syltlx20180077

Abstract(406) HTML (161) PDF(23)

Abstract:
In order grasp the working characteristics of anti-icing systems of the helicopter rotor, the turboshaft engine and the inlet under icing conditions, the helicopter artificial icing tests were conducted. The icing tests were conducted in different liquid water contents, at different temperatures, and under both ground and hovering conditions. The interaction between the rotor, the engine and the inlet anti-icing systems was studied. It is found that the right inlet ices easier than the left side due to rotor rotating. The inlet has a poor anti-icing performance when the engine works under low power condition, and its performance improves when the engine power rises. The engine power condition rises after rotor icing, leading to a higher inlet temperature than that in the dry air. The periodical icing-shedding on the rotor results in an engine parameter fluctuation. The fluctuation period is hardly affected by the environmental condition, while the fluctuation amplitude changes linearly with the liquid water content.

Focused laser differential interferometry measurement of instability wave in a hypersonic boundary-layer

Yu Tao, Zhang Wei, Zhang Yifeng, Chen jiufen, Chen Jianqiang, Wu Jie

2019, 33(5): 70-75. doi: 10.11729/syltlx20190076

Abstract(276) HTML (139) PDF(28)

Abstract:
The wind tunnel experiment is one of the most important methods to conduct the hypersonic boundary-layer transition research. However, the experimental technology that can be used for three-dimensional hypersonic boundary-layer measurement is still extremely lacking, and the dynamic response of the existing measurement technology is quite restricted. In order to solve the above problems, a non-instrusive Focused Laser Differential Interferometry (FLDI) measurement system is set up based on the light refraction and interference principle and it can effectively measure the density disturbance of the flow field at spatial points. A hypersonic laminar/turbulent boundary-layer transition experiment was carried out on a 7° half angle sharp cone model in a conventional Mach 8 hypersonic wind tunnel with FLDI being the main diagnostic. The results show that FLDI successfully captures the second mode instability wave at 327 kHz and its 645 kHz harmonics. In comparison with PCB test results, FLDI has the advantages of high Signal to Noise Ratio, high dynamic response and high spatial resolution (less than 1 mm along the flow direction). Considering its excellent characteristics such as high spatial and temporal resolution, FLDI can be used as a promising diagnostic for the hypersonic boundary-layer transition and receptivity study.

Accurate infrared radiance measurement of H₂O₂-kerosene rocket engine flume

Chen Hao, Li Shuaihui, Chen She, Li Sen, Li Teng, Wei Xiaolin, Yu Xilong, Fan Jing

2019, 33(5): 76-80, 86. doi: 10.11729/syltlx20180171

Abstract(352) HTML (188) PDF(19)

Abstract:
The quantitative measurement of infrared radiation (IR) of the attitude and orbit control rocket engine flume plays a key role in the aircraft penetration effectiveness research and in verification of the numerical simulation of the rocket engine flume flow field. In order to study the IR field of the rocket engine flume quantitatively, an experiment is conducted to measure the IR characteristics of the flume of one H₂O₂-kerosene small rocket engine. A cooled midwave infrared camera with a spectral band of 3.7~4.8 μm is developed. The detector, which has a mean NETD of 16 mK and an output resolution of 16 bits, is highly sensitive and has a wide dynamic range. With radiation calibration and calibration error analysis, the obtained grayscale images are converted, and the IR field distribution of the engine flume in the midwave infrared spectral band is acquired. The experiment result shows distinct Mach disks in the plume, and the peak radiation of the plume in the midwave infrared spectral band is 184 W/(m²·sr) with a measurement accuracy of 12 W/(m²·sr).

Atomic emission spectroscopy diagnostics for leak detection of cooling water in a low-enthalpy arc heater

Lin Xin, Zeng hui, Peng Jinlong, Ou Dongbin, Li Fei, Yu Xilong

2019, 33(5): 81-86. doi: 10.11729/syltlx20180174

Abstract(193) HTML (106) PDF(3)

Abstract:
Arc-heated facilities play an important role in the development of thermal protection materials and heat shield structures for entry vehicles. Owing to the intensive heat fluxes generated by the arc root at the electrode surface, the erosion of the electrode is inevitable and there exists a risk of the cooling water leaking from the electrodes due to the accumulation erosion of the electrode material. It is well acknowledged that the arc heater can be severely damaged due to the late leak detection. Therefore, the development of fast response and accurately quantitative diagnostic techniques for leak detection of cooling water in an arc heater would be highly beneficial. Due to the harsh conditions inside the arc heater, especially for the low-enthalpy arc heater (total enthalpy range:2~12 MJ/kg), choices for the diagnostic methods are limited. Optical emission spectroscopy (OES) is a powerful tool to probe atoms and molecules which has been used in many areas such as chemical kinetics, non-equilibrium radiation, and so on. This paper presents an experimental investigation of the application of OES in the leak detection of cooling water for a low-enthalpy arc-heated wind tunnel (FD-04). According to the spectral characteristics of the high-temperature flow field in the FD-04 arc heater, the 777.19 nm emission spectral line of the atomic oxygen (O_777.19) is utilized for monitoring the operating status and determining the leakage of the cooling water. A relative intensity determination method for the O_777.19 emission is proposed and water leakage failures are successfully diagnosed under two test conditions at total enthalpy values of 11.6 and 9.8 MJ/kg. A solution is proposed that the diagnostic technology keeps high enough sensitivity for multiple total enthalpy conditions. This work demonstrates the potential of using the OES technique for leak detection of cooling-water in a low-enthalpy arc-heated facility.

Thrust/drag calibrations for integral inlet and jet testing on a aircraft with blended wing/body

Wu Chaojun, Hu Buyuan, Li Dong, Wu Fuzhang, Chen Qisheng

2019, 33(5): 87-92. doi: 10.11729/syltlx20180141

Abstract(200) HTML (88) PDF(7)

Abstract:
When researching on the influence of the inlet and jet exhaust plume of the embedded propulsion system on the aerodynamic characteristics of a blended wing/body aircraft, a calibration method of thrust and drag for the integral inlet and jet simulation test is developed. The embedded ejector integrated with the aircraft model is employed to simulate the inlet and jet effects simultaneously. The total value of the aerodynamic load on the aircraft model and the thrust of the working ejector are measured by the balance. With the TPS calibration tank, the thrust and drag of the propulsion system can be calibrated, the decoupling of the aerodynamic load on the aircraft model with the thrust and drag of the propulsion system can be efficaciously realized, and the reliability data of inlet and jet effects can be obtained. The thrust/drag calibration method is verified by the inlet and jet simultaneously testing with black-embedded inlets of a blended wing/body aircraft.

Development of coaxial rigid rotor test stand for Φ3.2m wind tunnel

Huang Mingqi, Yang Yongdong, Liang Jian, Peng Xianmin, Tang Min

2019, 33(5): 93-97. doi: 10.11729/syltlx20180135

Abstract(204) HTML (119) PDF(8)

Abstract:
To meet the needs of the wind tunnel experiment, China aerodynamics research and development center successfully developed the Φ3.2 m coaxial rigid rotor stand for wind tunnel experiments. The test of coaxial rigid rotor models with a diameter of 2 m can be carried out on this test stand. The upper and lower rotors are supported separately and rotate conversely. The coaxial rotor test stand realizes remote and synchronous real-time control over the rotor shaft angle, collective and cyclic pitch, and so on. From the iteration cycle of simulation-test-adjustment, dynamic issues of the test stand are addressed. The design parameters of the transmission system are selected carefully to guarantee the stability. The wind tunnel test results of the model coaxial rigid rotor show that the repeatability precision of thrust can be better than 0.58%, and the repeatability precision of torque can be better than 0.11%.

Design and processing of a continuous aero-elastic shell model of high-rise flexible structures

Wang Lei, Liu Wei, Fan Xingyan, Zhang Zhenhua, Liang Shuguo

2019, 33(5): 98-104. doi: 10.11729/syltlx20180152

Abstract(165) HTML (108) PDF(5)

Abstract:
The wind tunnel test of the aero-elastic model is an accurate method to assess the wind effect on the high-flexible structures, and the model making is the key point during this process. A novel method to make the continuous aero-elastic shell model is proposed, and the main steps as well as key techniques of the model manufacture are discussed in detail. Firstly, the inner mold is made of gypsum, the outer mold is carved by organic glass, and the gap dimension between the inner and outer mold is precisely designed in this step. After that, the DEVCON glue is injected into the gap. Finally, the inner and outer mold is removed after the glue is cured, and then the aero-elastic model is done. Dynamic test results show that the mass, the damping ratio, the first two order mode shape and the frequency of the realistic structure could be simulated accurately. The making method of this article has the following advantages:low time-consuming, economic, high precision and good versatility. Moreover, this method can be used for the continuous aero-elastic model of high-rise buildings, high-rise flexible chimneys, chemical towers, TV towers, cooling towers and so on. So the making method proposed in this paper can be an important guideline for the similar structures.

Design and debugging of the liquid nitrogen storage device in continuous transonic wind tunnel cooling system

Li Feng, Gao Chao, Xi Zhongxiang, Zhang Guobiao

2019, 33(5): 105-110. doi: 10.11729/syltlx20180131

Abstract(194) HTML (112) PDF(8)

Abstract:
The low temperature operation is an effective way to improve the Reynolds number in wind tunnel experiments. By means of liquid nitrogen injection, the first cooling system for the NF-6 continuous transonic wind tunnel has been built in China. The overall scheme and main technical indicators of the liquid nitrogen injection cooling system in NF-6 wind tunnel are introduced. The structure and technical principles of the liquid nitrogen storage device of the cooling system are expounded and the static and dynamic debugging results are presented. Test results indicate that our calculation method of the liquid nitrogen consumption is correct and it provides theoretical references for volume estimation of the liquid nitrogen tank. The scheme design of the liquid nitrogen storage device is reasonable and the liquid nitrogen injecting process is smooth and unimpeded. Meanwhile, the self-pressurized system of the liquid nitrogen storage device is working well and the heat-insulating properties of the liquid nitrogen tank can meet the requirements of the cryogenic liquid nitrogen storage.The daily evaporation rate of the liquid nitrogen in the tank is 0.044%, far lower than the designed index.The liquid nitrogen storage device has a good match with the whole cooling system. Throughout the debugging process, the key indicators such as the total temperature, total pressure, Mach number and running time have reached design requirements and excellent performance was achieved.

2019 Vol. 33, No. 5