实验流体力学

Research progress of the ice crystal icing in aero-engine

SHEN Hao, HAN Bingbing, ZHANG Lifen

2020, 34(6): 1-7. doi: 10.11729/syltlx20190124

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Abstract:
It is believed that the temperature of air compressed by fan is higher than the freezing point, therefore the compressor would not freeze. However, researchers found in several engine thrust loss accidents occurred in recent years that the ice crystal can lead to compressor icing. The researchers have reproduced this phenomenon in the lab. Ice crystal icing research in the area of aero-engine has just started in China. In this paper, the ice crystal icing issues are analyzed and discussed from both numerical research and experimental research aspects. The highlight and limitation are also included. The research focus which should be paid attention to is proposed in the end. This paper can give some reference for engine icing study and certification.

Aerodynamic design and numerical simulation of combined cycle nozzle with small length to height ratio

GE Wenxing, GUI Feng, YUAN Huacheng, HE Mofan, GUO Rongwei

2020, 34(6): 8-17. doi: 10.11729/syltlx20190142

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Abstract:
A preliminary study on the aerodynamic design of the combined cycle nozzle working in the range Ma=0~6.0 with small length to height ratio was carried out under strong geometric restricts. The line of the nozzle was designed by the method of characteristic. The effects of the design Mach number, the three-dimensional lateral expansion angle and the relative position of the two nozzles on the aerodynamic performance were studied. A nozzle aerodynamic design scheme considering both the effective utilization of space and the aerodynamic performance was presented. The numerical simulation results show that reducing the Mach number at the design points can improve the performance of the combined cycle nozzles during the subsonic flight and avoid serious overexpansion of the nozzles. With the increase of the lateral expansion angle, the aerodynamic performance of the nozzle that keeps the exit height unchanged at high Mach number is superior, while the aerodynamic performance of the nozzle at low Mach number decreases seriously. The relative position of the turbine engine and the ramjet nozzle outlet has a great influence on the aerodynamic performance of the transition point, and there is an optimal position layout, which achieves the optimal thrust performance. The thrust coefficient of the combined cycle nozzle is about 0.920 at the designed Mach number. The flow field is smooth transition during the transition mode, when the thrust coefficient is not less than 0.918.

Mass flux measurement and comparison study of simulation and experiment on curved cone waverider forebody inlet

HE Xuzhao, ZHOU Zheng, ZHANG Juntao, HE Yuanyuan, WU Yingchuan

2020, 34(6): 18-23. doi: 10.11729/syltlx20190095

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Abstract:
The mass flow capture performance is a key characteristic of the integrated Curved Cone Waverider forebody Inlet(CCWI). Delicate mass flow measurement experiment and comparison studies between experiment and simulation are conducted for obtaining the CCWI's mass flow capture ratio. Using the mass flow measurement experimental system, the CCWI's mass flow capture and static pressure distribution are obtained at free stream flow Mach number(Ma_∞)3.0, 3.5 and 4.0, Angle of Attack (AOA) from -4° to 6°。Comparison studies of CFD simulation and experiment are carried out at Ma_∞=4.0, AOA from -4° to 6°。Based on the verified CFD software and simulation methods, the mass flux and compression performance of the CCWI are examined at Ma_∞=4.0 and 6.0. The results show that the average square error of the mass flux measurement is less than 2%. Simulation and experimental results agree well with each other. The CCWI has good flow compression abilities and its mass capture ratios are 0.60, 0.68 and 1.00 at Ma_∞=3.5, 4.0 and 6.0, AOA=0° respectively.

Experimental study of aerodynamic damping characteristics of a launch vehicle with boosters in transonic flow

JI Chen, WU Yansen, HOU Yingyu, ZHU Jian, LIU Wenbin, BAI Kui, LIU Ziqiang

2020, 34(6): 24-31. doi: 10.11729/syltlx20200034

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Abstract:
The aerodynamic-damping and frequency characteristics of a launch vehicle with boosters vibrating in the first free-free bending mode, and the influence of the reduced frequency on aerodynamic damping were experimentally studied in a transonic wind tunnel. The test Mach number ranged from 0.70 to 1.05, and the angle of attack ranged from 0° to 10°. The result shows that for the elastic model with boosters, the aerodynamic damping and modal frequency are affected by the angle of attack while the trend is not obvious. The aerodynamic damping changes with the Mach number. The transonic dip appears near the Mach number of 0.90. The modal frequency of the first mode decreases with the increase of the Mach number. The reduced frequency has some effect on the aerodynamic damping that when Mach number ranged from 0.70 to 0.90 and after 1.00, the aerodynamic damping decreases with the increase of the reduced frequency, while Mach number ranged from 0.92 to 0.98, the aerodynamic damping increases with the increase of the reduced frequency.

Departure characteristics of blended-wing-body aircraft

FU Junquan, SHI Zhiwei, CHEN Jie, ZHOU Mengbei, WU Dawei, PAN Lijun

2020, 34(6): 32-37. doi: 10.11729/syltlx20190110

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Abstract:
Static force measurements of blended-wing-body aircraft at high angles of attack were carried out in the 1 m low speed wind tunnel of Nanjing University of Aeronautics and Astronautics. By fully mining and analyzing the experimental results, the approximate initial departure angle of attack and departure region of BWB aircraft are obtained by using multiple criteria, including the static stability derivative, the dynamic directional stability parameter, the lateral control departure parameter and the Weissman chart. Besides, the spin sensitive region of BWB aircraft is predicted. At the same time, the departure is simulated by the virtual flight test in wind tunnel. The results show that the lateral stability of BWB aircraft is poor, and the non-command roll motion may occur at a very small angle of attack, which is also the main reason for the divergence of the departure. And the departure characteristics obtained from the virtual flight test and these stability criteria are in good consistency, which verifies the reliability of the virtual flight test in departure characteristics research.

Experimental study on starting characteristics of vertical axis wind turbine with resistance wind-cup structure

BAI Yuedi, TONG Guoqiang, JIANG Yu, LI Yan, FENG Fang, ZHAO Bin

2020, 34(6): 38-44, 65. doi: 10.11729/syltlx20190105

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Abstract:
In order to improve the starting characteristics of SB-VAWT, a wind-cup structure is installed inside the wind turbine. Through static torque wind tunnel test and PIV visualization test, the influence of wind-cup structure on the starting characteristics of double-blade SB-VAWT is studied. The results show that the wind-cup structure has a significant influence on the inner flow of the SB-VAWT. At some azimuth angles, the flow separation phenomenon at the tail of SB-VAWT lift blade is improved by the wind-cup structure, and the vortex is weakened, reducing the energy loss. In a rotation period, the existence of the wind-cup structure also produces the torque acting on the rotor axis, so the static starting moment of the vertical axis wind turbine with the wind-cup structure is higher than the static starting moment of SB-VAWT.

Study on buffet flight test of aircraft with T-tail

GAO Wentao, ZHANG Wulin, KOU Baozhi

2020, 34(6): 45-51. doi: 10.11729/syltlx20200040

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Abstract:
This paper introduces the aircraft buffet mechanism, the research developments of buffet flight tests of the domestic and overseas, the buffet flight test methods, and the advantages and disadvantages of the methods. Then theoretical analysis was performed on the wind-up turn method. The methods, such as the velocity reduction method and the wind-up turn method, were used in the flight test. Acceleration transducers were put on the horizontal tail and the floor under the pilot's chair, in order to obtain the buffet response under different flight conditions. The buffet response at different locations was obtained by analyzing the root mean square(RMS) and frequency spectrum of the buffet response data. The buffet response of the trailing edge of the tip of the horizontal tail is the most violent. The buffet response increases with the increase of both the angle of attack and Mach number. The horizontal tail's buffet response mainly centralizes on the 1^st-order symmetric bending, the 2^nd-order anti-symmetric bending model frequencies of the horizontal tail and the 1^st-order symmetric bending model frequency of the wing. The buffet response at the pilot's seat location centralizes on the 1^st-order symmetric bending model frequency of the horizontal tail. The aircraft buffet response can influence the comfort of the pilot. Both vibration responses at the pilot's seat location and the wing surface structures should be considered to establish the buffet boundary.

Research on the effect of tubing on turbulence in inlet wind tunnel test

XU Binbin, WU Chaojun, WANG Xue

2020, 34(6): 52-58. doi: 10.11729/syltlx20190118

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Abstract:
Turbulence can be calculated through the fluctuating pressure in the inlet wind tunnel test. The accuracy of the fluctuating pressure measurment depends on the tubing ahead of the fluctuating pressure sensors. In this paper, the effects of tubing on turbulence are researched based on the dissipation model of dynamics and are verified by the inlet wind tunnel tests. The research results show that the tubing ahead of the sensor has a serious effect on the turbulence. The amplitude of the fluctuating pressure increases and the measured turbulence is magnified when the effect of tubing exits. In order to eliminate the error brought by the tubing, the way using tubing to measure fluctuating pressure should be avoided in the inlet wind tunnel test. If the tubing is inextricably used in test and the length of tubing is more than 5 mm, the final fluctuating pressure data should be revised.

Experimental investigation on the wind pressure on the platform screen door of a subway station

ZENG Lingwei, YI Fumin, WANG Hanfeng, Li Liangqiao

2020, 34(6): 59-65. doi: 10.11729/syltlx20190149

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Abstract:
Using moving model tests, the pressure distribution and variation inside a tunnel and on a Platform Screen Door (PSD) have been investigated for the cases of a train passing the tunnel, passing the station and tracing. The scale ratio of the standard A⁺ subway train model is 1:20. It is found that a pressure wave is generated when the train is passing the shaft of the tunnel, which is similar to the situation when a train is entering a tunnel except for the smaller extreme pressure value. For the case of a train passing a station, the pressure on the PSD is dominated by the pressure wave transfering through the tunnel; when the train reaches the station, this pressure experiences another extreme value, and then shifts to a negative extreme value immediately when the train's head passes the PSD. These extreme pressures determine the strength design criteria for the PSD. For the train tracing case, the pressure on the PSD reaches its extreme value caused by the pressure wave when the coming train is still at a distance from the station. Then, this pressure decreases slightly and keeps approximately constant for a period. This lateral pressure is the reason why the PSD cannot open or close properly.

Transition measurement for the nature-laminar wing based on TSP technique

WU Ning, TANG Xin, DUAN Zhuoyi, ZHANG Yanjun

2020, 34(6): 66-70. doi: 10.11729/syltlx20190085

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Abstract:
In order to verify the design results of a laminar flow wing, a high-speed wind tunnel test was carried out in the DNW-HST wind tunnel in the Netherlands, and the transition position of the boundary layer on the wing surface was measured by the TSP method in the test. The experimental results show that the TSP method is very effective in detecting the transition position of the natural laminar airfoil surface. At the same time, it is found that the test has high requirements on the surface finish of the wing, and the test results are very sensitive to the surface pollution of the wing.

Research on the calculation of pressure loss in continuous transonic wind tunnel

LI Qingli, MENG Fanmin, LI Xinglong, ZHANG Ren, CUI Xiaochun

2020, 34(6): 71-78. doi: 10.11729/syltlx20190139

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Abstract:
In order to meet the demand of the development of advanced aerospace models in the future, the construction of large-scale transonic wind tunnels has been carried out. Since the construction of large-scale continuous transonic wind tunnels has never been carried out in the past, construction experience is limited. The estimation pressure loss of the continuous wind tunnel and the calculation of aerodynamic parameters of various parts are the design input conditions for the wind tunnel structure system, measurement and control system, and power system. The accuracy of pressure loss estimation results directly affects the difficulty of the wind tunnel power system design. Using the classical pressure loss calculation method combined with the CFD numerical simulation, this paper comprehensively analyzes the key parts of the loss and the results of scaled section test, and gives the loss coefficient of the special section, especially that of the test section, more accurately. The iterative calculation method gives the aerodynamic performance of each section accurately. Finally, by comparing the estimated value of the wind tunnel pressure loss with the test results of 0.6 m continuous wind tunnel, the estimated uncertainty is within 7.5%.

Research on semiconductor strain gage balance technology applied in shock tunnel

HUANG Jun, QIU Huacheng, LIU Shiran, ZHAO Rongjuan, LYU Zhiguo, YANG Yanguang

2020, 34(6): 79-85. doi: 10.11729/syltlx20190122

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Abstract:
The conventional strain balance or piezoelectric balance cannot meet the requirements of high precision aerodynamic measurement in the shock tunnel, as the effective test time is very short. The strain sensitivity of the semiconductor strain gage is much higher than that of the foil strain gage, but its temperature coefficient is two orders of magnitude greater than that of the foil strain gage. This paper designed a temperature-self-compensation semiconductor strain gage, and applied it on equal strength beam experiments. The results show that the temperature self-compensation technology can effectively improve the temperature effect of the semiconductor strain gage, and the temperature drift of the semiconductor strain gage is reduced down to 0.2% FS after temperature compensation. In this paper, a six-components balance with high frequency response is designed for the shock tunnel, and the results of calibration show that the combining loading repeatability and combining loading error of the balance meet the requirements of the national military standards. The balance can acquire more than one signal during effective test time as the inherent frequency of the test system is more than 100 Hz, and the results of the shock tunnel test are in good agreement with reference values of the aerodynamic manual and CFD results.

Self-innovated ALTP heat-flux sensor and its performance tests

YANG Kai, ZHU Tao, WANG Xiong, TAO Bowan, ZHU Xinxin, WANG Hui, YANG Qingtao

2020, 34(6): 86-91. doi: 10.11729/syltlx20190148

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Abstract:
The transverse Seebeck effect is used to develop the ALTP heat-flux sensor for the high-frequency-pulse heat flux density measurement in hypervelocity wind tunnel tests. The self-innovated ALTP heat-flux sensor is statically calibrated with the xeon short arc lamp calibration system. And the sensitive coefficient is about 8.24 μV/(kW·m^-2), which is larger than the sensitive coefficient 6.90 μV/(kW·m^-2) of the ALTP heat-flux sensor developed abroad. Then an experiment was conducted in a shock wind tunnel to get the sensor's response time in comparison with thin-film-resistance heat-flux sensors, and the response time of the ALTP heat-flux sensor is less than 0.20 μs.

2020, 34(6): 91-91.

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2020, 34(6): 92-99.

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2020 Vol. 34, No. 6