实验流体力学

Hypersonic boundary layer transition simulation of complex configuration using γ-Re_θ transition model

Yi Miaorong, Zhao Huiyong, Le Jialing

2018, 32(4): 1-11. doi: 10.11729/syltlx20180019

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Abstract:
The correlation-based γ-Re_θ transition model has been implemented into a large scale parallel compressible Navier-Stokes solver AHL3D. In order to simulate the effects of compressibility of the hypersonic flow, compressible modification has been added into this model. The constant parameter for the separation induced transition has been enhanced to improve the ability of the forced transition simulation. The correlation equations have been adjusted after all the modifications. In order to validate the modified models' ability to capture the transition location, a Ma=7.4 Ames all-body aircraft model for natural transition and a Ma=6 flat plate installed with three dimensional roughness elements for forced transition were simulated. The results show that compared to the original model, the modified model gives much later transition location and stronger effects of the roughness elements, which agree well with the experimental results. Finally, the modified model has been applied to the simulation of hypersonic natural and forced transition of the 20% scale X-51A fore body configuration in BAM6QT. The present model can simulate not only the effects of the free stream turbulence intensity but also the promotion of the transition position by the forced transition trips. The results show the good potential of the modified γ-Re_θ transition model in transition prediction for complex configurations in hypersonic flows.

Investigation on flow field characteristics of a rectangular scramjet in different combustion modes

He Can, Xing Jianwen, Xiao Baoguo, Deng Weixin, Liu Weixiong

2018, 32(4): 12-19. doi: 10.11729/syltlx20180022

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Abstract:
In order to investigate the flow field characteristics of an ethylene fueled rectangular scramjet in different combustion modes, three-dimensional steady Reynolds averaged Navier-Stokes simulations of the flowpath were employed on the basis of direct-connect experiments for four different equivalence ratios. The numerical and experimental results were compared. The distinguishing criterion of the combustion modes for this configuration was chosen. The regularities of the sidewall pressure and one-dimensional average Mach number distributions were discussed. And the detailed characteristics of the shock structure, the flow separation, and the combustion were analyzed. The results indicate that the simulation results are in excellent agreement with the ground-test data. Multiple reflections of the oblique shock waves and expansion fans result in the wall pressure fluctuation, and the shock system is mainly affected by the flowpath structure for Case Cold. In the scramjet-mode operation, the influence of the shock produced by the interaction between the flow and the injectors on the flow field is obvious, the pressure rise is anchored downstream of the injector, and the flameholder cavity is full of three-dimensional separated structures. In the dual-scramjet-mode operation, the oblique shock train induced by shock-boundary-layer interactions dominates the flow field structure, and the shock system is weak in the combustor. And some separation occurs closely behind the shock train leading edge in the corners of the isolator whereas the separated region reduces in the cavity. In the ramjet-mode operation, the shock features are similar to that in the dual-scramjet-mode operation. The separation regions expand in the isolator corner and reduce in the cavity with the upstream propagation of the shock train. Some combustion may occur in the isolator with the upstream propagation of the shock train for the dual-scramjet-mode and ramjet-mode operations, while in the scramjet-mode operation the combustion is conducted just in the cavity and expander, and the chemical reaction and high temperature distributions are more concentrated.

Model for three-dimensional distribution of liquid fuel in supersonic crossflows

Wu Liyin, Zhang Kouli, Li Chenyang, Li Qinglian

2018, 32(4): 20-30. doi: 10.11729/syltlx20170172

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Abstract:
The spatial oscillation distribution characteristics of liquid jet in a supersonic crossflow were studied experimentally. Two models were built for predicting the oscillation distribution in the longitudinal and three-dimensional space, respectively. The experiments were carried out in a blow-type wind tunnel with Mach number of 2.1, and various conditions were studied, including stagnation pressure of the supersonic airflow (642~1010kPa), nozzle diameters (0.48~2.07mm), distance down from nozzle (10~125mm), practical pressure ranges (0.5~4.5MPa), and jet-gas momentum flux ratio ranges (0.11~10). Pulse laser background imaging method (PLBI) was used to shoot the transient spray distribution structures from the side and PIV method was used to capture the structures in cross-sections. A key parameter (Spray Proportion, γ) was defined to quantify the spatial oscillation distribution of the spray. A longitudinal spray oscillation distribution study was carried out, a spray boundary band model was established, and the model accuracy was verified. In addition, a piecewise function of the egg-shape curve and parabola was adopted to fit the contour line to establish the model for the spatial distribution of the spray in the cross-section. Based on various cross-section distributions with multi-parameters, a mathematical model is proposed to describe the liquid spray spatial distribution.

Experimental study on the fine structures and pressure characteristic of the shock train in the isolator

Kong Xiaoping, Chen Zhi, Zhang Kouli, Chang Yu, Zhu Yangzhu, Gong Hongming

2018, 32(4): 31-38. doi: 10.11729/syltlx20170178

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Abstract:
Experimental studies on the fine structures of the transient flow and the pressure measurement of the shock train in a constant area isolator with T-control and without controlling method are performed. To study the three dimensional structure of the shock train, the oriented schlieren technique and the nano-tracer planar laser scattering(NPLS) technique are used. The flow visualization results show that these two techniques can obtain the flow structures. Compared with the oriented schlieren, the NPLS technique can catch the fine structures of the flow such as the boundary layer of the turbulence, fine structures of the shock train and the separation area. With the interaction of shock train and vortex induced by the T shaped generator, the shock train edge is bifurcated and closely followed by the second similar structure. High frequency pressure measurements are conducted to reveal the shock train movement and its frequency-domain feature. The shock train location and its movements are detected by conventional statistical methods and the approach of pressure derivative integral. It is revealed that the approach of pressure derivative integral can detect the shock train arriving effectively.

Shear layer correction methods for open-jet wind tunnel phased array test

Zhang Jun, Wang Xunnian, Zhang Junlong, Lu Xiangyu, Chen Zhengwu

2018, 32(4): 39-46. doi: 10.11729/syltlx20180013

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Abstract:
To identify the true location of the noise sources, the shear layer effect must be taking into account when conducting the microphone array test in open-jet wind tunnels. An experimental study for the shear layer correction was performed in the 0.55m×0.40m aero-acoustic tunnel of China Aerodynamics Research and Development Center(CARDC). The shear layer velocity profiles, source-receiver delay times and source identification results were obtained. The Gortler's velocity-profile solution was validated and four different shear layer correction methods were compared and analyzed on the basis of the experimental results. The research results show that:the velocity-profile experimental data agrees well with calculations when the self-similar parameters σ=9, ξ₀=0.2 are chosen, and the relationship between the fitted shear layer thickness and the axial distance data can be presented by the equation y=0.15x; Ma ≤ 0.3 and the measurement angle θ_m within 40°~140°, the relative calculation error of the delay time of different shear layer correction methods is smaller than 1%; the accuracy of the other three methods are quite close to the Amiet 2D method. A fast ray tracing method that is 100 times faster than the conventional ray tracing method is proposed, which makes the ray tracing method applicable for on-line microphone array data processing.

Experimental research of the plate film cooling characteristics of backward-expanding shoulder arm hole

Huang Kang, Wang Hongbiao, Huang Hui, Ma Husheng, Zong Youhai

2018, 32(4): 47-52, 71. doi: 10.11729/syltlx20170137

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Abstract:
A new turbine film-cooling hole shape that is named the backward-expanding shoulder arm hole is designed. By using N₂ and CO₂ gas as the cooling gas, the film cooling perfor-mance with different density ratios of the backward-expanding shoulder arm hole, the circular hole and the shoulder arm hole is studied in the paper. The results show that, under the same conditions the film cooling efficiency of the backward-expanding shoulder arm hole is better than that of the circular hole and the shoulder arm hole, and the film cooling efficiency of the shoulder arm hole is slightly higher than that of the circular hole. The average film cooling efficiency decreases with the increase of the blowing ratio in the place where x/D < 15, and the average film cooling efficiency at Br=1.0 reaches maximum in the place where x/D > 15 when the density ratio is 1.0. The average film cooling efficiency increases first and then decreases with the increase of the blowing ratio, and the average film cooling efficiency is highest at Br=1.0 is maximum. The analysis indicates that as the outlet velocity is higher when the density is lower under the same blowing ratio, so that the cooling gas is more easily blown away from the cooling wall, the blow-ing ratio has effects on the film cooling efficiency of the backward-expanding shoulder arm hole.

Experimental investigation on large aircraft afterbody vortices under the influence of horizontal tail tip vortices

Wang Xiao, Qin Suyang, Xiang Yang, Wang Fuxin, Liu Hong

2018, 32(4): 53-60. doi: 10.11729/syltlx20170149

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Abstract:
The vortex system of a large aircraft afterbody includes a counter-rotating vortex pair (APV) generated by the afterbody separated flow and horizontal tail tip vortices (HTV). The characteristics of the vortices of a simplified afterbody with and without horizontal tails were measured in the wind tunnel using PIV. APV shifts upwards when moving downwards. A four-vortex system is observed for the afterbodies with horizontal tails. APV is significantly affected by HTV:APV shifts upwards faster and moves outwards in spanwise direction; the existence of HTV strongly reduces the vorticity strength of APV. The restraint effect becomes stronger as the span of horizontal tail decreases. Inflow speed has little to do with non-dimensional parameters of the vortices under low speed conditions.

Research on interference effect of super large cooling towers with two tower combinations under complex mountains

Ke Shitang, Yu Wenlin, Wang Hao, Zhu Peng, Yu Wei, Du Lingyun

2018, 32(4): 61-71. doi: 10.11729/syltlx20180044

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Abstract:
Taking a domestic super large cooling tower which is the world's tallest (210m) as an example, the flow field information and pressure distribution patterns of two cooling tower combinations were obtained considering complex mountains (close to the cooling tower, the height of which is close to the cooling tower throat elevation) based on wind tunnel experiments and CFD numerical simulation methods. On this basis, maximum negative pressures, interference factors based on the extremum of the negative wind pressure and mean wind pressures were analyzed, and then the wind-induced interference mechanism between the mountain and the towers were studied under the most unfavorable conditions. Studies show that the distribution rules of interference factors of cooling towers based on the extremum of the negative wind pressure obtained by wind tunnel experiments and CFD numerical simulation methods, respectively, are the same, and the maximum interference factors obtained by the two methods are 8% different. Complex mountains have significant influence on the flow turbulence and wind pressure distribution patterns of cooling towers. Influenced by the "channel effect" between cooling towers and buildings, the interference factor based on the extremum of the negative wind pressure under the worst condition is up to 1.586, significantly greater than the common interference factors without complex mountains.

Study on supersonic turbulence plate ablation flow field in arc heater

Yang Hong, Luo Yue, Wu Dong, Zhou Ping

2018, 32(4): 72-77. doi: 10.11729/syltlx20170181

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Abstract:
The supersonic turbulent plate ablation test technology is an important method in arc-heater to study the ablation characteristic of thermal protection materials. In order to study the change of the flow field during the supersonic turbulence plate ablation, a numerical simulation method based on N-S equation is adopted. The simulation results of the initial model surface parameters are in good agreement with the experimental results. Then, the flow field simulation about the model contour is carried out in the experimental process, which is compared with the experimental flow field. The changes of surface pressure and heat flux on the model are analyzed. According to the analysis, if the maximum ablation position is in the high heat flux region of the initial model, the ablation rate can be calculated by using the maximum ablation amount.

Assessment and measurement of total pressure distortion based on five-hole-probe for S-shaped inlet

Xu Zhulin, Gao Rongzhao, Da Xingya

2018, 32(4): 78-86. doi: 10.11729/syltlx20170130

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Abstract:
The assessment and measurement of total pressure distortion of the inlet is significant in the assessment of the integration of the inlet and engine. S-shaped inlet possesses great stealth performance, but the complex fluid field in the outlet contributes to error in the measurement and assessment, which impedes the integration of the inlet and engine. The experimental results show that the sector fitting is suitable for data processing of total pressure in the S-shaped inlet. The circumferential total pressure distortion index increases from 0.005 to 0.09 while the maximum radial index not exceeding 0.055 with the increase of Mach number from 0.2 to 0.6. The higher Mach number is, the severer total pressure distortion is. Total pressure recovery index of the main area of total pressure distortion in outlet is below 0.85. In total, compared with numerical computation and the rake measurement, the results of five-hole-probe measurement are more comprehensive and rational.

Investigation of wind tunnel balance dynamic characteristics' multi-order inertial compensation

Ai Di, Xu Xiaobin, Wang Xiong

2018, 32(4): 87-92. doi: 10.11729/syltlx20170161

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Abstract:
The structural vibration of the aerodynamic measurement system can be actuated by impulse loads or dynamic loads in aerodynamic measurement tests of hypersonic wind tunnels. Therefore, the useful data and the vibration noise are mingled. The accuracy of the present balance dynamic compensation method is poor since the processing method is over simplified. We simplify the force measurement system to a cantilever beam with an end mass determined by its structural characteristics, and obtain its analytical solutions for free vibration. Study of the free vibration is focused on the impacts of different vibration shapes on force measurement, and the distribution disciplines of acceleration of different vibration shapes. We put forward a new compensation method named 'multi-order inertial compensation method', and obtain the corresponding theoretical compensation coefficients. What's more, we validate this method by finite element analysis and wavelet analysis. The results show that the multi-order inertial compensation method significantly improves the dynamic characteristics of the balance compared with conventional method.

Research on microphone phase array design based on surrogate model

Ding Cunwei, Li Zhoufu, Zhang Xue, Zhou Guocheng

2018, 32(4): 93-98, 103. doi: 10.11729/syltlx20170151

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Abstract:
In aero-acoustic wind tunnel tests, the improvement of the microphone phase array according to the noise source features must be conducted as fast as possible to ensure the required efficiency of the tests. An optimization method based on the Kriging surrogate model is proposed in this study. The maximum sidelobe level and the resolution of the microphone phase array are obtained by analyzing the results computed from the point spread function. A Kringing surrogate model is constructed based on the response values computed on sample points. Then the surrogate model was utilized to fast assess the maximum sidelobe level and the resolution of the microphone phase array, which avoided the high computational cost caused by computing the point spread function. This method can improve the performance of the microphone phase array effectively for aero-acoustic wind tunnel tests.

Experimental investigation on aerodynamic performance of hypersonic wind tunnel two-stage ejector

Guo Xiaoguo, Jiang Zepeng, Chen Xing, Wang Tiejin

2018, 32(4): 99-103. doi: 10.11729/syltlx20170041

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Abstract:
The aerodynamic performance of the two-stage supersonic ejector is investigated by the Ma5~6 experiment on the FD-07 wind tunnel of CAAA. The experimental data is acquired by the test of the second stage ejector, the combined test of the first and the second stage ejectors, and the combined test of the main flow and the secondary flow. The conclusion can be organized as followed:(1) The ejector operating efficiency is higher and medium pressure gas consumption is less when the work pressure ratio of the two-stage ejector is setted to 0.8MPa and 1.0MPa, respecticely. (2) The low pressure environment of the test section is mainly determined by the main air flow. As far as the start-up pressure ratio of the wind tunnel is satisfied, the ope-rating parameters of the ejector have little effect on the pressure of the test section. (3) The first-stage supersonic ejector can be well segregated from the main airflow disturbance and the second-stage supersonic airlow interference, which is instructive for the theoretical study of the multi-stage ejector. The research work is carried out with the actual wind tunnel as the object, and effectively solves the problem that the running state of the FD-07 wind tunnel ejector is not clear. The ejector operating pressure scheme has been optimized so to be energy saving, and it has practical significance for the hypersonic wind tunnel performance improvement. The relevant test data can provide a reference for the study of aerodynamic performance of the supersonic ejector.

2018 Vol. 32, No. 4