实验流体力学

Experimental and theoretical model study on effective thermal conductivity of SOFC porous electrode

Huang Zhipeng, Zhao Mengtian, Yang Xigang, Wang Yuzhang

2019, 33(6): 1-6. doi: 10.11729/syltlx20190018

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Abstract:
The flow heat transfer and chemical reaction inside the Solid Oxide Fuel Cell (SOFC) are complex, and it is easy to generate thermal imbalance zones. Obtaining high-precision effective thermal conductivity of porous electrodes is of great significance for the establishment of numerical analysis models of multi-physics field coupling and the thermal management. In this paper, an experimental platform and measurement system for the effective heat conduction system of porous materials was designed and constructed, which is based on the steady-state method. The temperature distribution of the porous electrode test specimens was measured in detail in the temperature range of 372.1~932.4K. Through the theoretical analysis of heat transfer in porous materials, the calculation model of the comprehensive effective thermal conductivity of temperature-corrected SOFC porous electrodes was constructed using the scale factor t, which combines the existing EMT and ME1 mathematical models. In addition, the validity and high precision of the effective thermal conductivity model were verified by comparing the calculated values with the experimental measurements of the surface temperatures of the three test specimens with the porosity of 0.2349~0.4178.

The influence of rotor rotation of hexacopter on wind measurement accuracy

Li Zhengnong, Hu Haohui, Shen Yijun

2019, 33(6): 7-14. doi: 10.11729/syltlx20190047

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Abstract:
MUAV (Micro Unmanned Aerial Vehicle) can replace the mast to measure the wind field at a fixed point or multiple points at the same time, but the disturbance caused by the rotor rotation can affect the wind measurement accuracy. An ultrasonic anemometer is attached on a hexacopter using different height brackets, and wind tunnel tests are carried out to investigate the influence of the rotor rotation on the wind field at different heights above the center of the hexacopter and the influence of different wind directions and the tilted fuselage on the measurement accuracy. The results show that rotor rotation causes a great relative wind speed error except for a few situations; The wind speed error caused by the rotor rotation increases first and then decreases with height; when the fuselage is horizontal, the absolute wind speed error tends to be the same under various conditions as the height increases, and when the control wind speed is greater than 6 m/s, the relative wind speed error decreases as the wind speed increases. Rotor rotation has almost no influence on the measurement of the wind direction angle. The results can provide reference for the practical application of wind measurement using MUAVs equipped with wind measurement devices.

Electrical Bond number effects on the instability of charged ethanol micro-jet in electrosprays

Huo Yuanping, Wang Junfeng, Zuo Ziwen, Liu Hailong

2019, 33(6): 15-21. doi: 10.11729/syltlx20180113

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Abstract:
This paper presents an experimental study on the evolution of charged ethanol atomization modes and the instability of the micro-jet. Based on the high-speed microscopy and small scale PIV technology, the microstructure evolution process of the charged ethanol micro-jet was accurately captured, the jet instability evolution characteristics of different atomization models and its influence on atomization characteristics under the effect of the electrical Bond number were discussed. The results show that the jet's non-axisymmetric radial disturbance occurs throughout the jet atomization models. As the electrical Bond number increases, the jet flow deviation increases first and decreases subsequently. The uncertainty fluctuation range gradually increases in the cone jet mode, while it gradually narrows down to zero and increases again in the multi-jet mode. The jet core and its velocity direction of the cone-jet mode all deviate from the axis, and the jet speed significantly declines compared with the spindle mode. The velocity of the jet core obviously rises when the jet transits to the multi-jet mode, while the velocity distribution has many differences at different electrical Bond numbers. The jet boundary streamline shows disorder and lack of symmetry most of the time. However, a stable multi-jet mode with a peak velocity occurs for a very short interval of the electrical Bond number.

Investigation on flow turbulent characteristics of plate-fin and tube-fin heat exchanger

Fu Cheng, Zhao Bo, Xu Dachuan, Liao Daxiong, Pei Haitao, Zhu Bo, Qin Honggang

2019, 33(6): 22-27. doi: 10.11729/syltlx20190036

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Abstract:
In the continuous wind tunnel, the heat exchanger is installed upstream the test section to balance the heat which is generated by the fan or the compressor to control the total temperature in the test section. The heat exchange efficiency and the total pressure loose ratio are two important performance parameters of the heat exchanger in the wind tunnel. On the other hand, the flow dynamic characteristics such as the turbulence intensity and the noise of the heat exchanger can influence the flow dynamic quality of the wind tunnel significantly. In the 0.55 m×0.40 m low noise aeronautics acoustic wind tunnel, the hot wire is used to measure the velocity and the turbulence intensity distribution downstream the tube-fin heat exchanger and the plate-fin heat exchanger, and the total pressure loose ratio is also gained. The CFD method is used to simulate the flow structure and the self-turbulent intensity of these two types of heat exchangers. The study results show that the flow straightening characteristics of the tube-fin heat exchanger and the plate-fin heat exchanger have significant differences. The turbulent intensity and velocity uniformity downstream the tube-fin heat exchanger are better than that downstream the plate-fin heat exchanger, while the plate-fin heat exchanger has better straightening performance on horizontal turbulence. The self-turbulent intensity of the plate-fin heat exchanger is lower than the tube-fin heat exchanger. The investigation has important engineering application value for design of large scale continuous wind tunnels which have advanced flow quality requirements.

Study on the efficiency of a new central-type diffuser for hypersonic low density wind tunnel

Bi Lin, Li Zhenqian, Tang Zhigong, Yuan Xianxu, Chen Hao

2019, 33(6): 28-33. doi: 10.11729/syltlx20190063

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Abstract:
The diffuser is one of the key components of the supersonic and hypersonic wind tunnels, which directly affects the efficiency-cost ratio of the wind tunnel operation. However, for the hypersonic low density wind tunnel, the range of operating parameters is large and the test gas density is relatively low, and thus the effects of the conventional diffuser with "contraction section, equi-straight section and expansion section" are not obvious. In this paper, a new central-type diffuser structure is presented, and the efficiency of the central-type diffuser is tested at the Φ300 mm hypersonic low density wind tunnel for M16 small flow rate states and M8 large flow rate states. At the same time, the influence of the test section model on the diffuser's capacity is analyzed. The results show that the central-type diffuser has a wide range of operation parameters and a significant pressure increase efficiency, and can effectively improve the wind tunnel test capability. This study can provide a reference for the design of the hypersonic wind tunnel diffuser.

Effects of the high temperature exhaust plume reaction on lateral jet interactions

Zhang Qingbing, Lu Xueling, Sha Sha

2019, 33(6): 34-40. doi: 10.11729/syltlx20180161

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Abstract:
A cold jet exhaust or a somewhat equivalent gas jet exhaust or a non-reacting gas mixture exhaust is usually adopted to study the jet interaction effects in experimental or computational work, but problems may arise in the design work of an advanced future vehicle using a divert thruster. Firstly the experimental and computational results in the available literatures about the influence of different gas models on the force and moment are reviewed. Then as a supplement study result, the forces and moments acting on the body, and the peak aerodynamic heating exerting on the lateral jet interaction areas by the cold jet exhaust plume, the non-reacting mixture jet exhaust plume and the reacting mixture exhaust plume models are presented for a typical cone-cylinder-flare body with a practical-use high momentum ratio divert jet. The calculated results show that when the lateral jet is turned off the chemical reactions have very limited influence on the forces and moments, but when the lateral jet is turned on the three different gas models give 4%~15% difference for normal forces and about 20% difference for interaction pitching moments. As the cold jet model can not be used to predict the aerodynamic heating property the chemical reaction effects on the peak aerodynamic heating exerting on the lateral jet interaction areas are studied by comparison between the non-reacting gas mixture model and the reacting gas mixture model, and 13% increase is found when considering the chemical effects. The lateral interaction mechanical property and peak heating results for the cone-cylinder-flare body with practical-use high-momentum ratio divert jet put forward a demand for experimental verification reproducing high temperature exhaust plume reaction effects.

Research on measurement of airfoil drag for transonic wind tunnel experiment based on wake integral method

Xu Siwen, Gao Chao, Zhang Zhengke

2019, 33(6): 41-45. doi: 10.11729/syltlx20180047

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Abstract:
The shape, the height and the installation location of the wake rake have some influence on the airfoil drag when the airfoil drag is measured by the wake integral method in the wind tunnel experiment. The airfoil experiments have been carried out in NF-6 transonic wind tunnel for two wake rakes with different heights respectively at two installation locations in the experimental section with the OA309 airfoil. By comparing and analyzing the experimental data of different installation locations with the same height of the wake rake and the experimental data of wake rakes with different heights at the same installation location, the suitable combination of the wake rake height and the installation location needed for different experimental conditions has been obtained, which provides references for drag measurement in the transonic airfoil wind tunnel.

Research progress of test technologies for 3 m×2 m icing wind tunnel

Ni Zhangsong, Liu Senyun, Wang Qiao, Wang Zixu, Guo Long

2019, 33(6): 46-53. doi: 10.11729/syltlx20180115

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Abstract:
The 3 m×2 m icing wind tunnel was built in 2013. A lot of progresses have been made in the research of the wind tunnel test technologies in recent years. This paper presents the basic situations and test technologies of the 3 m×2 m icing wind tunnel, including overall situation, technical indexes and test capabilities. The status of the conventional icing and anti-icing test technologies in the 3 m×2 m icing wind tunnel, such as the calibration of cloud parameters, the capture of ice characteristics, the anti-icing technology using hot air and the de-icing technology using electrics are described in detail. From the view of engineering application and basic research, the research trend of test technologies in the fields of aircraft engines, helicopters, supercooled large droplets (SLD), and ice crystals are highlighted and analyzed. The development ideas and methods are put forward from the perspective of independent innovation. This paper provides a reference for the research on the construction and test technology development for the icing wind tunnel.

Internal mass flow control technology of low speed TPS tests

Hu Buyuan, Huang Yong, Zhang Guichuan, Zhang Rongping

2019, 33(6): 54-58. doi: 10.11729/syltlx20180201

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Abstract:
The TPS testing technology is one of the best methods to study the aircraft/propulsion integrated design in wind tunnels. TPS units, used as engine simulators, are driven by high pressure air. As a result, the mass flow control accuracy of high pressure air has a direct relationship with the wind tunnel testing accuracy. Because of space limits of wind tunnel testing models, the external mass flow control method can not control more than 2 TPS units. In order to overcome deficiencies of the external mass flow control method, a kind of internal mass flow control device was designed. This device integrates the control and measure function, and can control 4 TPS units simultaneously. A check test was conducted in the TPS testing chamber of CARDC. The testing results indicate that the device has good linear mass flow control ability, the control resolution is better than 0.15 g/s, and the control repeatability accuracy is better than 3 g/s. A full model TPS test was conducted in the 8 m×6 m low speed wind tunnel of CARDC as well. The repeatability testing accuracy meets the demands of GJB, which verifies the control accuracy of the device.

Precise stagnation point heat flux measurement technique of sharp leading edges

Zhang Yang, Jia Guangsen, Sha Xinguo, Chen Xing

2019, 33(6): 59-64. doi: 10.11729/syltlx20180112

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Abstract:
In order to improve the aerodynamic performance, a sharp leading edge is widely used in the hypersonic flight vehicles, which exerts a huge challenge on thermal protection systems. The sharpness of the leading edge makes it hard to measure the stagnation point heat flux precisely. In this paper, an integral sensor with high spatial resolution is developed to measure the stagnation point heat flux, and the corresponding estimation method is adopted as well. A wedge model with an interchangeable nose(R=1.0, 2.0 and 5.0 mm) is employed to validate the effectiveness of the sensor, and a series of experiments are conducted at the FD-20 impulse wind tunnel under the condition of Mach number of 4, 5, 6 and 8. The results indicate that the difference of the stagnation point heat flux values is less than 15% between experimental measurement and theoretical prediction.

A design of total pressure control method for continuous transonic wind tunnel

Chen Dan, Zhang Yongshuang, Li Gang, Guo Shouchun, Shen Mou

2019, 33(6): 65-71. doi: 10.11729/syltlx20180094

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Abstract:
The total pressure is the key indicator of the continuous transonic wind tunnel. The high control precision of the total pressure can improve the accuracy of the test data, and the fast adjustment speed is of great significance for shortening the time of the Mach polar curve. According to the main characteristics of the continuous transonic wind tunnel, such as the presence of various test conditions and many adjusting means of the flow field, the characteristics of the pressure regulating system and the coupling characteristics of different adjusting means for the continuous transonic wind tunnel have been analyzed firstly. Then the control precision of the total pressure and the characteristics of the regulating valve have been obtained for the continuous transonic wind tunnel. The valves combination strategy is designed according to different test conditions. Lastly the control algorithm of the segmented variable parameter combined with the fuzzy PID is used to adjust the total pressure accurately. The result of the wind tunnel test shows that while guaranteeing the time of each Mach pole curve, the total pressure control accuracy reaches 0.1% and the control strategy can adapt to the control requirement of the total pressure control for the continuous transonic wind tunnel.

Study on varying dynamic pressure control of flow field in 2m supersonic wind tunnel

Zhou Bo, Gao Chuan, Yang Yang

2019, 33(6): 72-77. doi: 10.11729/syltlx20180133

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Abstract:
The flutter test requires that the wind tunnel must have the capability of varying dynamic speed pressure. Therefore, the flow field control method was studied in the 2m supersonic wind tunnel. For the problem that the regulating characteristics of the main pressure regulating valve are not consistent when the total pressure is running in a wide range of steps, the method of the total pressure grouping and error segmentation control is adopted to solve the problem. The control method based on the characteristic curve of the main pressure regulating valve is adopted to meet the requirements of adjustable total pressure rise rate, which avoids the process of setting control parameters and requires fewer times of debugging. Test results show that the method can complete multiple total pressure control in a test, the main pressure stable precision reaches 0.3%, the overshoot of the dynamic pressure is less than 0.5kPa, and the total pressure rise rate is adjustable. The 2m supersonic wind tunnel has the capability of varying dynamic speed pressure, and has been successfully applied in the model test.

Influence of different sub-grid scale models on simulation accuracy of aerodynamic noise

Yin Xiang, Wang Yiping, Du Mintao, Su Chuqi, Sun Hao

2019, 33(6): 78-83. doi: 10.11729/syltlx20190109

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Abstract:
Based on different sub-grid scale models, the Large Eddy Simulation (LES) is used to calculate the unsteady flow field and sound field of the Hyundai Simple Model (HSM). The experimental data of the internal monitoring points of the model are used to verify the simulation results. The results show that using the WMLES model can get more accurate results.

Experimental investigation of the unsteady wake of the square-back Ahmed model

Fan Yajun, Xia Chao, Ge Diandian, Yang Zhigang

2019, 33(6): 84-89. doi: 10.11729/syltlx20190112

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Abstract:
The square-back Ahmed model is a simplified commercial vehicle body model. The flow separates at the tail to form a recirculation region, leading to the negative pressure on the back and large aerodynamic drag. The unsteady wake of the 1/4-scale square back Ahmed model were finely measured and statistically analyzed via the wind tunnel test. The experimental Reynolds number was 9.2×10⁴. The results of the back pressure measurement, particle image velocimetry (PIV) and hot-wire measurement show that the unsteady wake pattern of the square back Ahmed model basically consists of three flow characteristics: the bi-stable behavior (random asymmetry between the left and right vortex structures), vortex shedding in the horizontal and vertical direction, and pumping of the recirculation region periodically. Among them, the bi-stable phenomenon plays a dominant role in the wake. It shows the alternating occurrence of two stable states (the transition probability is 0.149). Each stable state can maintain a long time scale (the average duration is about 6 s), and its spectral characteristics satisfy the -2 power law distribution; the corresponding frequency of the periodic pumping oscillation is Sr_H=0.07; and the vortex shedding frequencies corresponding to the oscillations in the horizontal direction and the vertical direction are Sr_H=0.13 and Sr_H=0.17, respectively. The interaction among these structures exists, and thus the unsteady wake of the square back Ahmed model presents complex three-dimensional features.

Evaluation of simplified automobile wind noise model based on main propagation path of sound and vibration

Wang Yigang, Jiao Yan, Zhang Jie

2019, 33(6): 90-94. doi: 10.11729/syltlx20190106

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A Statistical Energy Analysis (SEA) model was established for a real vehicle. The main propagation paths were classified by the analysis of propagation characteristics, and the simplified model approximation analysis was performed. By choosing the main and secondary systems in the SEA model, two simplified models are established, and the calculation of their interior noise and propagation path shows that the characteristics of the model subsystem change, the energy propagation path and size characteristics change, and even the subsystem's ability to accept the external fluid pulsation and sound field changes, resulting in the change of the calculated interior noise. The use of the simplified model requires further study.

2019, 33(6): 95-102.

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Abstract:

2019 Vol. 33, No. 6