实验流体力学

Advances of research on internal cryogenic strain gauge balance abroad

Zhao Li, Zou Manling, Tian Jinglin, Yang Xi

2016, 30(6): 1-9. doi: 10.11729/syltlx20160090

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Abstract:
Cryogenic balance is the key measurement in cryogenic wind tunnel. Due to low air temperature and large temperature variation in the cryogenic wind tunnel, a series of problems arise, such as thermal zero drift and the variation of sensitivity. Therefore there is a risk of decreasing precision of the test data. Thus compared to conventional balances, the development of the cryogenic balance has more requirements and difficulties. By a wide literature survey, the key elements of cryogenic balance are sorted out as follows:design and optimization of balance, material selection and thermal treatment, processing and manufacturing of balance, matching of strain gauge, moisture treatment of balance at low ambient temperature, balance calibration algorithm as well as calibration apparatus and data acquisition equipment. A prospect of the cryogenic balance technologies is also given. The research results presented in this paper are of reference value for development and engineering application of cryogenic balance.

The influence of the tip sails shape on the wing aerodynamics in ground effect

Sun Chenghong, Dai chin

2016, 30(6): 10-17. doi: 10.11729/syltlx20160054

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Abstract:
The function of the wing tip sails is to scatter the concentrated tip vortices into several smaller scale vortex structures, and accelerate the dissipation of tip vortices, thereby reducing the induced drag. In order to study the influence of wing tip sails on the flow fields and aerodynamics of a wing in ground effect, wind tunnel experiment is conducted to measure aerodynamics and tip vortex structures of a NACA4412 wing fitted with three elliptic tip sails and three trapezoidal tip sails respectively, and the reason of the differences between the aerodynamic loads on the two wings is analyzed by comparing the flow fields of tip vortices. The lift and drag forces are measured using a 6-component balance, the velocity distribution of tip vortices is scanned by a 7-hole probe. The Reynolds number based on the chord length of the wing is 1.5×10⁵. The experimental results show that the differences of lift and drag forces between the two wings increase as the wings get closer to the ground, and the trapezoidal tip sails is more efficient in lift augmentation-drag reduction than the elliptic tip sails. The local flow direction and local incidence of each sails are different for the two wings, which result in different contributions in increasing the lift and reducing the drag.

Thermodynamic characteristic analysis of the cryogenic wind tunnel diffuser section based on fluid-thermal-structural coupling

Zhang Zhiqiu, Chen Zhenhua, Nie Xutao, Yao Chengwei

2016, 30(6): 18-25. doi: 10.11729/syltlx20160100

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Abstract:
In cooling down process, the cryogenic wind tunnel has a wide range of temperature variation, which may lead to strong structural thermal stress and affect equipment smooth and safe operation. The cryogenic wind tunnel diffuser section is investigated in this paper based on fluid-thermal-structural coupling. The data exchange interface for multiple physical fields, MpCCI, is adopted to combine the structural finite element software, Abaqus, and Computational Fluid Dynamics (CFD) software, Fluent. The fluid-thermal-structural coupling model of the diffuser section is established to investigate heat transfer characteristics of the cryogenic internal flow field and calculate the distribution of temperature and stress in the cryogenic wind tunnel structure. The cryogenic wind tunnel experiment indicates that the results of fluid-thermal-structural co-simulation agree well with the test results, which reflect correctly the thermodynamic characteristic of cryogenic wind tunnel structure and provide reliable analysis method for safety performance optimization of wind tunnel structure.

Investigation of heat transfer and flame dynamics under acoustic excitation based on infrared and shadow method

Deng Kai, Li Hua, Yang Zangjian, Zhong Yingjie

2016, 30(6): 26-31. doi: 10.11729/syltlx20160069

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Abstract:
The heat transfer of partially premixed laminar flame under Rijke acoustic standing wave was investigated. The flame dynamics and hot products could be captured by the infrared images and the radial temperature gradient distribution could be shown by schlieren imaging. The relationship between the hot products and the radial temperature is characterized with infrared-schlieren information integration. The results show that the hot products attached on the flame front under acoustic excitation present a symmetric structure of tip layer distribution. And the downstream region is wider than the upstream region. In one sound cycle the axial heat evolution shows a tip shape transporting heat to the downstream of the flame through two lifting processes. The temperature gradient induced by the radial heat transfer takes a finger shape whose evolvement is decided by the development of the cusps.

Experimental study of axisymmetrical dissemination of liquid driven by shock wave

Yang Lei, Yang Xianglong, Huang Zhongwei

2016, 30(6): 32-36. doi: 10.11729/syltlx20160060

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Abstract:
An experimental device for the axisymmetrical dissemination of liquid was set up. Applying the high-speed photography technology, the time series of the instability development at the gas/liquid interface and the primary breakup were recorded. The experimental results show that the increase of Mach number will lead not only to the decrease of the wavelength and the increase of the wave number of initial disturbance waves, but also to the degree of mixing of the spike and airflow. The positions of the primary breakup of the liquid don't change with the increase of the shock wave. The acceleration of the liquid front remains unchanged in the earlier stage and rises rapidly in the later stage.

Predication and wind tunnel experimental verification of thermal protection performance for low density ablative material in medium thermal environment

Gao Jiayi, Du Tao, Shen Yingzhe, Wu Yitian, Liang Xin, Shen Dan

2016, 30(6): 37-42. doi: 10.11729/syltlx20160015

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Abstract:
Low density ablative material is developed to shield the spaceship from the high-enthalpy, low heating rate thermal environment during re-entry. As new vehicle projects develop, the low density ablative material is required to be able to work in the new medium thermal flux environment. In this paper, material test pieces are evaluated in the arc heated wind tunnel with high-enthalpy, medium thermal condition. In the experiment, high-performance insulation material is installed between the water-cooled frame and test pieces, which avoids lateral thermal leaking and improves the accuracy of the experiment. It shows the competence of the low density ablative material under the new thermal condition in experiments. At the same time, the calculation is carried out to evaluate the thermal protection performance of this material. The ablative mechanism of the low density ablative material is very complicated. In this paper, the computation method for carbonization ablation is improved by making use of different predication methods in different regions, based on the heat conduction-pyrogenation-carbonization mechanism of the low density ablative material. The theoretical prediction is compared with the data from wind tunnel experiments, showing that the prediction is consistent with the wind tunnel result.

Study on the flow of water sand slurry with sliding bed in inclined pipe

Zhao Li'an, Wang Tieli

2016, 30(6): 43-49. doi: 10.11729/syltlx20160073

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Abstract:
In order to further study sand particles' transport rules in the inclined slurry pipe associated with the sliding bed, force balance theories are used to study the method for evaluating the suspended layer and sliding bed velocities as well as the sliding bed thickness, and an iterative method for computing the deposit critical velocity is given. Meanwhile, the shear force linear distribution assumption is used and with the aid of prandt empirical formula, a velocity distribution model above the sliding bed is given. Experimental data of coarse sand pipe hydraulic transportation show that the deposit critical velocity is negatively correlated with the particle size and concentration, and it is positively correlated with the pipe dip angle when the transportation concentration is kept constant. The comparison between the calculated results and the measured results show that the maximum deviation of the calculated value from the measured value is 13%. The experimental data also shows that with the increase of the angle of the pipe, the maximum velocity point position has an upward trend. The comparison between the calculated and measured results shows that the deviation of the theoretical velocity distribution model and the measured value is not more than 10%. Results show that the force balance theory and the linear hypothesis of the shear stress distribution apply well in the research of deposition critical velocity and velocity distribution above sliding bed in the inclined coarse sand slurry pipe accompanied with the sliding bed.

Light field volumetric particle image velocimetry

Ding Junfei, Xu Shengming, Shi Shengxian

2016, 30(6): 50-58. doi: 10.11729/syltlx20160141

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Abstract:
A novel single camera volumetric velocity measurement technique is presented, which utilizes the advanced light field imaging technology to capture 3D PIV tracer particle images. The framework of Light Field Particle Image Velocimetry (LF-PIV) includes an in-house high resolution light field camera, multiplicative algebraic reconstruction technique (MART) based light field particle image reconstruction method and a ray tracing based synthetic light field particle image generation platform. The LF-PIV technique is compared with Tomographic Particle Image Velocimetry (Tomo-PIV) by using both synthetic DNS jet flow images as well as water jet experimental images. Results show that LF-PIV is capable of reconstructing the instantaneous volumetric velocity field with the accuracy similar to that of Tomo-PIV.

Velocity measurements for flows around micro-cylinder array based on image overlapping

Wang Haoli, Xu Ming

2016, 30(6): 59-65. doi: 10.11729/syltlx20160047

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Abstract:
In this study, the influence of depth of correlation (DOC) on the micro-PIV measurement is analyzed. The method of image overlapping under the low particle density condition can decrease DOC and improve the velocity measurement accuracy. This method is applied to the velocity measurements on multiple fluid planes for the flow around a micro-cylinder array under eight Reynolds numbers from 0.8 to 3.6, and the spatial averaged velocities (SAVs) are calculated based on the velocities. In order to analyze the measurement accuracy, the velocities and SAVs resulting from the method of image overlapping are compared to those obtained by the method of average cross-correlation. The results indicate that of the image overlapping is a more reasonable method under the low particle density condition. The average pseudo-slip velocity decreases by 22.7% for the bottom surface and 17.2% for the top, respectively, and the average peak velocity increases by about 5.2%.

Design and implementationfor full field of view measurement scheme in vertical wind tunnel

Ma Jun, Song Jin, Liu Bei, Qin Sanchun, Xiong Jianjun, Jiang Min

2016, 30(6): 66-70, 104. doi: 10.11729/syltlx20160087

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Abstract:
Spin is a kind of abnormal state of aircraft, complicated and dangerous. It can easily cause flight accident. Spin experiment in vertical wind tunnel is one of the main research technical means. The purpose is to obtain the attitude angle of model aircraft in experimental process, for analysis of its spin characteristics. The paper concentrates its attention on the characteristics of spin motion and the application defect of binocular measurement system in previous experiments. The full field of view measurement scheme is designed, and the research for the key technologies is carried out. The coded marker recognition technology is adopted to realize feature automatic identification. The 3D reconstruction technology based on rigid body is adopted to realize the measurement of model attitude. The date calibration based on the same reference plane is adopted to realize the effective data fusion within multiple angles of view. The effectiveness and reliability of the measurement technology is proved by spin experiment in vertical wind tunnel. The experiment curves are complete, and the image utilization reaches 95%. It provides richer data for characteristics analysis of spin phenomenon.

Preliminary study on energy-saving layout for conventional hypersonic wind tunnel

Wang Tiejin, Shi Yueding, Deng Zhiqiang, Huang Bingxiu

2016, 30(6): 71-75, 104. doi: 10.11729/syltlx20150133

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Abstract:
With the development of hypersonic vehicles, the large-scale conventional hypersonic wind tunnel with nozzle exit diameter of 2m order of magnitude is required. However, the energy consumption of the exhausting working air also increases dramatically in the large-scale tunnel. How to save energy while the simulation conditions for the development of hypersonic vehicles are satisfied has become an important problem to be considered in the design of the conventional hypersonic wind tunnel. To solve this problem, the layout of the conventional hypersonic wind tunnel is optimized as follows:first, the aerodynamic layouts of the existing conventional hypersonic wind tunnels are summarized; second, the energy transformation in the conventional hypersonic wind tunnel during its operation is theoretically analyzed, and from the point of view of saving energy also analyzed are the methods used to deal with the exhausting working air in different layouts; third, the possible methods for utilizing the remainder energy of the exhausting working air are discussed; finally, an optimized layout for the large-scale conventional hypersonic wind tunnel is put forward, and the critical technologies to be used in the realization of the layout are discussed. The result of a simple calculation of saved energy in the optimized layout under a typical run condition shows its advantages in saving energy.

Research on flutter test technique in supersonic wind tunnel

Yan Yu, Yu Li, Lyu Binbin, Luo Jianguo

2016, 30(6): 76-80. doi: 10.11729/syltlx20160078

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Abstract:
When the wind tunnel starts or ends running, there is a large impact load which could damage the flutter model easily. In order to solve the problem, a supersonic flutter insertion system is developed in FL-23 wind tunnel of CARDC. During the flutter tests, the insertion system pushes the model into the flow after the impact load disappears, and at the end of the tests or if the flutter occurs, the insertion system pulls the model back quickly. The test results show that the insertion system could protect the flutter model from damage effectively and ease the intensity limit of the model. The dynamic pressure achieved from the subcritical prediction is close to the flutter test result. As a conclusion, a practical supersonic flutter testing platform has been established in CARDC.

Technique for developing thin slab strain gauge balance based on rectangular beam

Shi Yujie, Wang Yuhua, Tian Zhengbo

2016, 30(6): 81-85. doi: 10.11729/syltlx20160082

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Abstract:
The thin slab strain gauge balance is often used in hinge moment force test and parts force test for aircraft in wind tunnel. Limited by the structure of the aircraft model, the stiffness of the conventional thin slab strain gauge balance at the connections is insufficient as compared with that of the balance elements, leading to low accuracy. In this study, each element of the thin slab balance is divided into multiple rectangular beams which together compose a new element. Using the new thin slab strain gauge balance can improve the accuracy of measurement. By traditional mechanical analysis, FEA, and tests the feasibility of the technique is shown, and it has already been used in several wind tunnel tests in China Aerodynamics Research and Development Center.

Development of a single-fixed sheet hinge moment balance with axial force measurement

Wang Shumin, Pan Huaye, Wang Chao, Ma Tao

2016, 30(6): 86-90. doi: 10.11729/syltlx20160003

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Abstract:
Restricted by the condition of the test model and the wind tunnel balance structure, it's hard to measure the aerodynamic loads of the control flap accurately by using the normal sheet hinge moment balance. The main reason is there is no axial force measurement on the typical hinge moment balance, and therefore the interference due to the axial force can't be avoided. Moreover, The data quality of the balance measurement is depressed seriously due to the wing flexibility. To solve this problem, we put efforts to optimize the balance structure at the High Speed Aerodynamic Institution of CARDC. We designed a single-fixed sheet hinge moment balance with axial force measurement, which has been used in a certain airplane model hinge moment test successfully. The results of the balance calibration and the test data show that this balance can measure the axial force effectively, almost eliminate the influence of the wing flexibility, and increase the matching characteristic of the forces by decreasing additional moment. Using this type of hinge moment balance can increase the quality of the test data efficiently.

The design of a 3-DOF robot arm used forcaptive trajectory simulation in wind tunnel test

Wei Ran, Che Binghui, Zhang Jun, Sun Chuanbao, Wang Xinlin

2016, 30(6): 91-97. doi: 10.11729/syltlx20150141

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Abstract:
A 3-DOF robot arm design is presented for the Captive Trajectory Simulation (CTS) test in the FL-12 wind tunnel. It is an integrated mechatronics device. The paper introduces its transmission principle design, physical design, control system design, drive element selection calculation and verification, then verifies the design results with dynamical and static mechanics analysis. The results show that the device improves the load in pitch and yaw from 100Nm to 250Nm with control precision from 0.1°to 0.05°, and also improves the load in roll from 10Nm to 20Nm with control precision from 0.1°to 0.05°.The structure of drive element and cable, fairing configuration, overall dimension are optimized to make the device more suitable for the wind tunnel test.

Design and realization of full flexible nozzle control system of the trans-supersonic wind tunnel

Gao Chuan, Rui Wei, Qin Jianhua, Wang Fei, Jiang Jingyan

2016, 30(6): 98-104. doi: 10.11729/syltlx20160071

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Abstract:
Flexible nozzle has to be designed long enough in order to ensure the elasticity of the nozzle wall material. The characteristics of long-span, large amount, complex structure of the actuators bring enormous challenge to the design of the flexible nozzle contour control system. It is not only needed to control the positon of each actuator precisely, but also to control motion axes for synchronization. The effect of synchronization control has a direct impact on the flexible plant forming quality and the wind tunnel flow quality. To solve the accurate positioning, multi-axis proportion synchronous control problems and to ensure safety of the full flexible nozzle in the new trans-supersonic wind tunnel of China Aerodynamics Research and Development Center, key technologies are researched. A virtual axis with the gearing synchronization strategy is proposed the redundant position technology axis is established and the control parameters is optimized based on SIMENS SIMOTION D and S120 motion control platform. The test results of actuators' displacement and servo motors' speed are analyzed based on the experiment of the multi-axis proportion synchronization motion system. The results show that the control system possesses complete functionality, that all the actuators can move uniformly in the range of 0~1mm/s, the tracking error is less than or equal to ±0.01mm/s, the proportion synchronization error is less than or equal to ±0.02mm/s, and the contour error before and after the nozzle throat point is less than or equal to ±0.2mm and ±0.06mm. The synchronization control precision and repeatability accuracy can meet the engineering application request and achieve good effect.

2016 Vol. 30, No. 6