实验流体力学

Progress of research on noise induced by compressible flow over cavities

Wang Xiansheng, Yang Dangguo, Liu Jun, Zhou Fangqi, Shi Ao

2018, 32(3): 1-16. doi: 10.11729/syltlx20170132

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Abstract:
The cavity is commonly employed in designing an aircraft. Nevertheless, the cavity flow, especially under high-speed conditions, is usually an important noise source, restricting the performance of the aircraft. The research progress on the cavity noise is summarized, including characteristics of the cavity oscillation, generation of the aeroacoustic noise, parameters which influence the cavity flow, and control of the cavity noise. The generation and propagation of the noise induced by the compressible flow over cavities are analyzed based on the characteristics of the unsteady cavity flow. Parameters that determine the cavity flow and noise are classified according to flow conditions, cavity geometry and structural vibrations. Furthermore, effects of these parameters on the cavity noise are considered, and the passive and active control techniques are summarized. Finally, challenges and future directions of researches on the cavity noise are outlined.

Measurements and applications of fast response pressure sensitive paint

Yu Jingbo, Xiang Xingju, Xiong Hongliang, Huang Zhan, Zhao xuejun

2018, 32(3): 17-32. doi: 10.11729/syltlx20180007

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Abstract:
The fast response pressure sensitive paint measurement technique has been developed quickly in recent years. A general review of this technique based on detailed investigation is presented. The characteristic, principle and dynamic response mechanism are described. Three kinds of porous structure fast response pressure sensitive paint are introduced, including TLC-PSP, AA-PSP and PC-PSP. Several dynamic calibration devices are introduced, including the shock wave tube, fast response solenoid valve, loudspeaker, jet oscillator and pulse jet. Different measurement methods are introduced including the point measurement, phase averaging, high speed acquiring, motion-capture measurement, life time method, and PSP microspheres method. Different application cases around the world are introduced, which manifests the advantages of the fast response PSP technique on the unsteady flow measurement.

Design and performance analysis of turbine based combined cycle inlet operation with Mach 0~4

Yuan Huacheng, Liu Jun, Guo Rongwei

2018, 32(3): 33-41. doi: 10.11729/syltlx20180005

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Abstract:
The turbine based combined cycle (TBCC) inlet was designed based on the thrust and mass-flow requirement of the TBCC propulsion system. The design points parameters of TBCC inlet, namely the captured area and the mode transition Mach number from turbine mode to ramjet mode were investigated through one-dimensional analysis of turbine engine and ramjet engine in this paper. Then the TBCC inlet scheme which can operate from Ma 0 to 4 was designed and its mode transition device was designed based on the translation scheme. The variable scheme of the TBCC inlet can be achieved through the single degree of freedom mechanism and the profile of the inlet operating at different Mach numbers was given. After the investigation of the length, control point values and the area diffusing rules of rectangular-to-circular shape diffuser of turbine flowpath, the numerical simulation results indicate that the diffuser length, control point values and the area diffusing rules have mild effects on the total pressure recovery and Mach number at the exit of the turbine flowpath, but control point values have significant effects on the distortion index. According to the results above, the diffuser length is chosen to be 3m, the value of the control point to be 1.5 and the area changing rule along the diffuser is chosen as a rapid turning at the entrance. The total pressure recovery of the TBCC inlet is 0.45 at Ma4.0 and 0.79 at Ma2.2, the distortion index is 0.15 at Ma2.2.

Investigation of the flame stabilization mechanism of the hydrocarbon fuel in the supersonic combustor

Song Wenyan, Shi Deyong, Wang Yuhang

2018, 32(3): 42-49. doi: 10.11729/syltlx20180017

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Abstract:
Supersonic kerosene combustion experiments were conducted at stagnation temperature of 1085K and inlet Mach number of 2.0. High speed camera was applied to observe the shape and structure of the flame. PLIF was used to observe the distributions of kerosene and OH. Flame stabilization mechanism was analyzed with the combination of numerical and experimental results. The experimental results show that the combustion reaction occurs in the downstream of the jet stream and in the cavity region. The spread angle and the penetration height of the flame are increased with the increase of the equivalence ratio. Numerical simulations show a reasonable agreement with the experimental results. The flame stabilization mechanism analysis indicates that the kerosene fuel is mostly distributed in the region near the floor after injected into the combustor in the liquid state. Combustion product with high temperature was transported into the cavity through the interaction between the cavity shear layer and the circulation. This process provides heat and radicals to the mixture of air-kerosene in the shear layer. Hence, the flame base is able to be stabilized in the shear layer and spread to the mainstream at a constant angle.

Investigation on the shock interactions between an incident shock and a plate with V-shaped blunt leading edge

Zhang Enlai, Li Zhufei, Li Yiming, Yang Jiming

2018, 32(3): 50-57. doi: 10.11729/syltlx20180002

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Abstract:
The cowl lip of a hypersonic inward-turning inlet is a critical region due to the complicated three dimensional shock interactions. To reveal these shock interactions and the inherent mechanisms, a simplified model of a plate with a V-shaped blunt leading edge was proposed to simulate the main characteristics of the cowl lip flow. Experimental observations in a shock tunnel in conjunction with numerical simulations were conducted to examine variations of the relative position of a wedge-induced forebody shock and the cowl lip. The results show that the stand-off distance of the bow shock in front of the stagnation point is large (compared with the bow shock of a cylinder with the same radius), followed by a wide subsonic flow region behind the bow shock. When the oblique shock impinges on the near normal part of the bow shock, Edney type Ⅳ a shock interaction occurs. On this occasion, the interaction between the incident shock and the bow shock is coupled with the shock interactions induced by the three dimensional flow over the V-shaped blunt leading edge, causing several regions of supersonic jet. When the oblique shock impinges on the subsonic region near the sonic point of the bow shock, a type of shock interaction that is different from the classification of Edney type Ⅲ is shown. When the oblique shock intersects with the bow shock at the supersonic region, the shock interaction structures are similar to the shock structures of Edney type Ⅱ and type Ⅵ. More attentions should be paid to the shock interaction problem of the V-shaped blunt leading edge cowl in the design of an inward-turning inlet.

Analysis of data correlation between impulse and continuous combustion heated facilities

Wu Yingchuan, He Yuanyuan, Zhang Xiaoqing, Lin Qi, Le Jialing

2018, 32(3): 58-63. doi: 10.11729/syltlx20180008

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Abstract:
The comparison tests of impulse and continuous combustion heated facilities were conducted. For Hydrogen-Oxygen combustion heated impulse and continuous facilities, the pressure coefficient distributions of the engine flow path were coincident but the engine thrust gain in continuous facility was 10% larger than that in the impulse facility. For Hydrogen-Oxygen combustion heated impulse facility and Alcohol-Oxygen combustion heated continuous facility, the pressure coefficient distributions of the engine flow path were coincident but the engine thrust gain in continuous facility was 5% larger than that in the impulse facility.

Analysis of data correlation between combustion heated impulse facility and hypersonic wind tunnel

He Yuanyuan, Wu Yingchuan, Zhang Xiaoqing, Lin Qi

2018, 32(3): 64-68. doi: 10.11729/syltlx20180011

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Abstract:
The simulation parameters of different hypersonic test facilities have large influence to the test results. A typical lift body aerodynamic test was conducted in the combustion heated impulse facility and hypersonic wind tunnel. The influence of Reynolds number and wall temperature ratio was analyzed. The aerodynamic changes of the combustion heated impulse facility test were in consistence with those of the hypersonic wind tunnel test, but its drag coefficients were about 15% larger. Numerical analysis indicates that the differences caused by Reynolds number were about 5%, and those caused by the wall temperature ratio were about 10%, and therefore the change of velocity boundary layer is the main factor.

Ballistic range measurement and numerical calculation of shock standoff distances in CO₂

Liao Dongjun, Liu Sen, Huang Jie, Jian Hexiang, Xie Aimin, Wang Zonghao

2018, 32(3): 69-74, 93. doi: 10.11729/syltlx20170157

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Abstract:
Measurement of shock standoff distances over spheres and the Mars entry vehicle model in CO₂ has been conducted in the hypervelocity ballistic range of Hypervelocity Aerodynamics Institute, China Aerodynamics Research and Development Center. Test models were spheres with the diameter of 10mm and entry vehicle models with the nose radius of 12.5mm. For spheres, the flight velocities were between 2.122 and 4.220km/s with ambient pressures between 2.42 and 12.3kPa. For the entry vehicle model, the flight velocity was 2.802km/s with the ambient pressure of 1.836kPa. Comparison was made between the test data and calculated results using the two-temperature nonequilibrium model. Under present test conditions, the two-temperature nonequilibrium model can basically reproduce the shock standoff distances over the test models. The flow over the test models is speculated to be mainly nonequilibrium. More test data with higher flight velocities (>5km/s) are needed for the validation of the two-temperature nonequilibrium model in CO₂ with higher freestream velocity. The influence of multi-temperature models and different chemical reaction models on the accuracy of the numerical simulation for the nonequlilbirum flow in CO₂ can be further studied.

Curved surface pressure measurement based on light-field imaging and PSP

Li Haotian, Xu Shengming, Zhao Zhou, Zhang Hanmo, Shi Shengxian

2018, 32(3): 75-81. doi: 10.11729/syltlx20180036

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Abstract:
This paper presents a novel single camera light-field three-dimensional pressure measurement technique (LF-3DPSP), which consists of light field 3D reconstruction and pressure sensitive paint. The technique uses a light-field camera to capture the wind-on, wind-off and model geometry images, which has a similar experimental procedure as the traditional 2D PSP method. The proposed technique was validated with a Ma5 truncated cone model test. The results show that LF-3DPSP is capable of measuring the surface pressure distribution on relatively large curvature 3D models with high accuracy, and the pressure results agree favourably with those of the schlieren test.

Measurement of turbulence velocity fluctuations in transonic wind tunnel using Interferometric Rayleigh Scattering diagnostic technique

Yang Furong, Chen Li, Yan Bo, Su Tie, Bao Weiyi, Chen Shuang

2018, 32(3): 82-86. doi: 10.11729/syltlx20170103

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Abstract:
The interferometric Rayleigh scattering diagnostic technique for the time-resolved velocity measurement of the transonic wind tunnel is studied. The velocity-measurement apparatus, consisted of a CW laser, a high resolution Fabry-Pérot interferometer and a high-speed EMCCD camera, is designed. Rayleigh scattering light is produced as the flow irradiated by the laser. Then the light is collected and analyzed accurately by the Fabry-Pérot interferometer and the camera. Theoretically, this systematic velocity-measurement accuracy can reach 1.23m/s. Measurement accuracy is then evaluated by comparing with hot wire anemometry results. Moreover, the distributions of velocity and turbulence intensity in a supersonic flow at Mach number 3.0 are obtained quantitatively. The sampling rate in this measurement reached about 4 kHz.

Visualization of shock wave in hypersonic flow using electric discharge

Sha Xinguo, Wen Shuai, Yuan Minglun, Lu Hongbo, Ji Feng

2018, 32(3): 87-93. doi: 10.11729/syltlx20170106

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Abstract:
Based on the relationship of the electric discharge radiation intensity and gas density, the electric discharge visualization system was set up in hypersonic impulse wind tunnel FD-20. Three different test models are employed to explore the practicability of electric discharge for visualization of hypersonic flow structures under the flow condition of mach number Ma=12.16 and static pressure p≈106Pa. The experimental models include a plate, a combination of a cube and a plate (labeled as plate-cube), and a simplified inlet. In the plate experiment, the shock wave between electrodes was accurately observed by the electric discharge and the shlieren respectively, and the two methods gave a merely 0.21° difference in the shock wave angle. In the plate-cube experiment, flow structures on two different slices were obtained by the electric discharge. Shock structures on the central plane slice are basically the same as those obtained by the schlieren and CFD, and shock structures on the slice far away from the central plane are also confirmed by CFD. In the simplified inlet experiment, a diamond shock cell was observed by the electric discharge in the internal flow region of the inlet. The measured size of the diamond shock cell is slightly different from the numerical result with a deviation of 7.9%. These results demonstrate that electric discharge can be used to visualize shock structures on different flow slices and the internal flow region in the hypersonic impulse wind tunnel, and is especially suitable for the observation of local complex flow structures.

Experimental investigation on response characteristics of PIV tracer particles in high speed flow

Wang Yanzhi, Chen Fang, Liu Hong, Sha Sha, Lu Xueling, Zhang Qingbing, Yue Lianjie

2018, 32(3): 94-99. doi: 10.11729/syltlx20170160

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Abstract:
The tracer's tracking ability is the key factor affecting the measurement accuracy of high speed PIV. Particle relaxation modeling is presented for high speed flow with the normal mach number over 1.4. Based on the combination of theoretical analysis and numerical simulations, high speed PIV and the tracer particle seeding technology are developed, and the quantificational measurement ability of PIV is improved. Recent experimental results were obtained by the Multi-Mach number high-speed wind tunnel in Shanghai JiaoTong university where titanium dioxides of various sizes were used as tracers in the Mach 4 wind tunnel to induce a 22° shock wave. The results reveal that the 30nm titanium dioxide particle is the most qualified option. Meanwhile, various shock wave experiments (including oblique shock wave and detached shock wave) were carried out to validate the particle tracing ability. In this paper, multiple experimental results are put forward to support the selection of tracer particles of high speed PIV.

2018 Vol. 32, No. 3