实验流体力学

Review of research on the receptivity of hypersonic boundary layer

Jiang Xianyang, Li Cunbiao

2017, 31(2): 1-11. doi: 10.11729/syltlx20160129

Abstract(882) HTML (305) PDF(107)

Abstract:
As a key aspect of transition prediction and control, receptivity process in hypersonic boundary layer is of great importance. However, it still has not been thoroughly understood, and is especially lacking in experimental verification. In this paper, two categories of disturbances are reviewed, namely, free-stream disturbance (acoustic, vertical, thermal perturbation, shock wave and particulates) and wall-induced disturbances (roughness, vibration, blowing and suction, surface heating and cooling). Mostly concerned are the theory of Fedorov about leading-edge receptivity and inter-modal exchange mechanism. In order to make the issue of receptivity more clearly understood, a compendious path diagram is sketched to describe paths to Mack modes.

Sublayer fence for wall shear stress measurement

Ma Chengyu, Ma Binghe, Deng Jinjun, Zhou Zitong, Zhang Han

2017, 31(2): 13-18. doi: 10.11729/syltlx20170010

Abstract(263) HTML (143) PDF(19)

Abstract:
This paper is a review of the sublayer fence for wall shear stress measurements in the turbulent boundary layer. A summary is presented of the main techniques for determining the skin friction that makes the sublayer-fence gauge an attractive approach for use in such environments. The directional surface-fence gauge for three-dimensional turbulent boundary layer measurements is also introduced. The micro sublayer fence utilizing Micro Electro-Mechanical Systems (MEMS) technology is a promising approach, and many concepts have been proposed. Finally, challenges faced in the development of process techniques are also outlined.

Review of the calibration methods and devices for wall shear stress

Yan Yuchao, Jiang Chengyu, Ma Binghe, Xue Xiaohan, Luo Jian

2017, 31(2): 20-25. doi: 10.11729/syltlx20170007

Abstract(193) HTML (128) PDF(18)

Abstract:
Wall shear stress measurement with micro sensors is an effective means to study the flow friction. It is fundamental and important work to calibrate the sensors accurately. Three static and two dynamic calibration methods are introduced in this paper. The calibration devices, working principles, and behavioral models of wall shear stress measurement are analyzed. The features of calibration methods are summarized, and advice is provided for selecting the proper calibration method.

Research progress on thermal wall shear stress sensors

Sun Baoyun, Ma Binghe, Deng Jinjun, Jiang Chengyu

2017, 31(2): 26-33, 43. doi: 10.11729/syltlx20170022

Abstract(303) HTML (121) PDF(27)

Abstract:
Micro Electro-Mechanical Systems (MEMS)-based shear stress sensors provide a significant method in wall shear stress measurement. In this paper, the research progress of thermal wall shear sensors is introduced. And the sensing principle, device structure, fabrication processes, and performance test of the silicon-based and flexible polymer-based thermal wall shear stress sensors are analyzed.

Design and development of MEMS based beam-membrane structure flow sensor

Chen Pei, Zhao Yulong, Tian Bian

2017, 31(2): 34-38. doi: 10.11729/syltlx20170001

Abstract(339) HTML (205) PDF(20)

Abstract:
Flow is one of the important parameters in industrial detection. With the development and application of the Micro Electro-Mechanical Systems (MEMS) technology, flow detection is developing towards miniaturization, high precision and intelligence. A MEMS beam-membrane structure based differential pressure flow sensor is designed, and its working principle is analyzed. The sensor is fabricated by the silicon micromachining technology, and then the airflow test and water flow test are conducted. The sensitivity by the airflow test is 0.3508mV/(ms^-1)² and the basic accuracy is 0.5885%FS. The sensitivity by the water flow test is 41.5241mV/(ms^-1)² and the basic accuracy is 0.9323%FS. The results show that the designed sensor has sufficient sensitivity and basic accuracy for the flow measurement.

Weak signal detection of MEMS hot-film wall shear stress sensors

Sun Hailang, Tian Yukui, Jin Lei, Zhang Xuan, Xie Hua

2017, 31(2): 39-43. doi: 10.11729/syltlx20170016

Abstract(272) HTML (103) PDF(5)

Abstract:
The weak signal of MEMS hot-film wall shear stress (WSS) sensors is hard to detect by direct amplification due to the inherent basic voltage. An effective method to solve this problem is proposed, which is to add an output-balancing system (OBS) before the signal is amplified. The basic voltage is decreased while the signal is retained. The development of the output-balancing system is presented, including the technical scheme, key technologies, examination and application.

High temperature dynamic pressure sensor and experimental analysis

Rahman·Hebibul, Wang Hongyan, Xue Fangzheng, Huang Linya, Huang Mimi, Yu Mingzhi, Zhao Libo

2017, 31(2): 44-50. doi: 10.11729/syltlx20170028

Abstract(295) HTML (130) PDF(17)

Abstract:
The inverted cup-type high-temperature piezoresistive pressure sensitive chip with the range of 25MPa was developed by the Micro Electro-Mechanical Systems (MEMS) and Silicon on Insulator (SOI) technology. The sensitive piezoresistors are isolated from the silicon substrate by the silicon dioxide, and thus the stability and reliability problems of the pressure sensitive chip are solved at high temperatures beyond 120℃. The flush-type mechanical packaging structure was designed to avoid the channeling effect and improve the dynamic response frequency of the sensor. For the fabricated high temperature dynamic pressure sensor, the static and dynamic performance experiments were carried out to obtain the sensor's fundamental performance and analyze its uncertainty at the static experimental temperature of 250℃. The results show that the sensor accuracy is ±0.114%FS and the uncertainty is 0.017 94mV. The thermal zero drift and thermal sensitivity drift were calculated. The dynamic response frequency was calculated as 555.6 kHz through dynamic performance experiment. Therefore, the developed MEMS pressure sensor has fine accuracy and high natural frequency at high temperatures.

Natural laminar-to-turbulent transition inside an electrically heated circular tube

Zhang Ruoling, Le Jialing

2017, 31(2): 51-60. doi: 10.11729/syltlx20150024

Abstract(201) HTML (117) PDF(9)

Abstract:
The natural laminar-to-turbulent transitional flow and convective heat transfer inside an electrically heated circular tube are analyzed. It is proposed that the transitional flow can be decomposed into the fully developed laminar flow and the turbulent flow, under the assumption that the fluctuating velocity in the radial direction does not change with varying flow modes. The composite ratios are adopted to define the composite flow, and they fluctuate during the flow transition. The minimum entropy production criterion is used to derive an equation which can describe the evolution of the transitional flow. It is deduced that the transitional behavior is governed by the fluctuations of the composite ratios. One fluctuation function is given to attain agreements with measurements including those obtained in heat transfer and flow experiments. It is pointed out that the process of the laminar-to-turbulent transition inside the tube can be compared with continuous phase transitions in a thermodynamic equilibrium system, and similar and separate processes for the transitions of the velocity and temperature inside the tube can be allowed.

Experimental study on the characteristic motion of bubble propelled hollow Janus microspheres

Zhang Jing, Zheng Xu, Wang Leilei, Cui Haihang, Li Zhanhua

2017, 31(2): 61-66. doi: 10.11729/syltlx20160152

Abstract(218) HTML (156) PDF(13)

Abstract:
This paper studies the bubble propelled motion of Pt-SiO₂ hollow Janus microspheres in H₂O₂ solutions (concentrations between 2% to 4%). Three typical stages have been observed in every period of the bubble growth-collapse, which are self-diffusiophoresis, bubble growth and bubble collapse. At the bubble collapse stage, the speed propelled by a microjet can reach tens of millimeter per second, and it is about 2 or 3 orders of magnitude higher than the speed in the other two stages. In the experiment, two scaling laws between the bubble radius and the elapsed time during the bubble growth stage are observed: R_b~t^1/3 and R_b~t^1/2. Because the bubble growing point at the Janus microsphere's Pt side deviates from the axisymmetric point, the trajectory of the Janus microsphere is nearly a circle.With the increase of the H₂O₂ concentrations, the speed of the Janus microspheres can be enhanced.This study not only quantifies the characteristic motion of Janus microspheres, but also provides valuable information for improving the speed and energy utilization of Janus micromotors in practical application.

Effect of confining pressure on the axial impact pressure of hydraulic jetting

Li Jingbin, Li Gensheng, Huang Zhongwei, Song Xianzhi, He Zhenguo

2017, 31(2): 67-72. doi: 10.11729/syltlx20160074

Abstract(264) HTML (136) PDF(4)

Abstract:
Hydraulic jetting techniques have found growing application in improving the rate of penetration (ROP) and enhancing oil recovery (EOR) in the oil and gas field. But it always encounters high confining pressure condition which may significantly weaken the performance of hydraulic jetting at the bottom of wells especially for the deep and ultra-deep wells, so it is crucially important to study the effect of the confining pressure on the high pressure jetting. A hydraulic jetting impact pressure measuring device which could generate low confining pressure ( < 10MPa) is used to measure the jet pressure and axial impact pressure. Results show that, with the method to build the confining pressure by changing the diameter of the outlet, the dimensionless jet pressure hardly changes until the dimensionless confining pressure exceeds a threshold which approximately equals to the square of the nozzle discharge coefficient, and from then on it increases with the confining pressure linearly; the confining pressure has no effect on the axial impact pressure within one nozzle diameter standoff distance; numerical fitting analysis show that the dimensionless axial hydrostatic pressure is proportional to the 3.3 power of the dimensionless confining pressure, and increases linearly with the dimensionless standoff distance; the dimensionless axial impact pressure is inversely proportional to the 0.15 power of the dimensionless confining pressure, and decreases linearly with the dimensionless standoff distance; but if the dimensionless confining pressure exceeds a threshold value which is between 0.6 and 0.7 in our study, the axial hydraulic static pressure will be in accord with the confining pressure, and the axial impact pressure won't change. This study provides helpful instruction for the hydraulic factor design for drilling, sand-flushing operation, et al.

Research on HIFiRE project's hypersonic vehicle integrated design of aerodynamic and scramjet propulsion

Deng Fan, Ye Youda, Jiao Zihan, Liu Hui

2017, 31(2): 73-80. doi: 10.11729/syltlx20160125

Abstract(586) HTML (269) PDF(57)

Abstract:
By the HIFiRE project, America and Australia have deeply investigated the aerodynamics, propulsion and controlling system of hypersonic aircrafts. The high-speed ability is evaluated for the integrated design of aircrafts with propulsion system. A series of valuable flight-data and staged achievements are obtained by the flight tests of single-target evaluation and step-by-step improvement, the principal study of waverider shapes and different propulsion systems, and the verification of designing condition by flight tests. The key technique and experimental conclusion are summarized for the overall design by organizing the flight tests of dynamics/propulsion integrated processes. Moreover, the developing trend is analyzed for the aircraft with propulsion system. The results show that the unit Reynolds number of the transition is between 3×10⁶ and 4×10⁶, and a combination of scramjet and waverider with high lift characteristics at small attack angle is the optimized design, which gives some suggestions for the overall design of high-speed aircrafts with scramjet.

Development of near-space-vehicle anemometer and calibration tests in low-temperature-low-static-pressure wind tunnel

Zhang Shiyu, Fu Zengliang, Zhao Junbo, Gao Qing, Qian Er

2017, 31(2): 81-85, 103. doi: 10.11729/syltlx20160137

Abstract(121) HTML (98) PDF(9)

Abstract:
A new kind of anemometer to measure the air speed of the near-space low speed vehicle is introduced in this paper. This equipment is designed based on the theory that rotating the measuring arms increases the acquired dynamic pressure. Benefitted from this theory, the anemometer can measure the wind speed with reasonable precision in situations of ultralow dynamic pressure in the near space environment. A series of tests are completed in the near-space environment simulation wind tunnel in the 21th Research Institute of CETC, whose inflow air speed is available from 5 to 14 meters per second. The results show that the measured dynamic pressure curves are coincident with the sine function curves and there is a significant linear correlation between the amplitude of the dynamic pressure and the inflow airspeed. Based on the linear fit method, a calibration model of the anemometer is established.

CFD analysis of the arc heater turbulent flow field of flat plate testing

Luo Yue, Zhou Wei, Yang Hong, Chen Wei

2017, 31(2): 86-92. doi: 10.11729/syltlx20160088

Abstract(173) HTML (81) PDF(3)

Abstract:
The statement debugging is important but time-consuming work in the arc-heated turbulent flat plate testing. Specially, with the development of the alerting angle method in recent years, the debugging becomes more complex and further consuming in both time and cost. In order to guide the experiments, some CFD analyses of the flow characteristics under different testing conditions are completed with the FLUENT software. By comparing to the experimental measurements of a calibration-plate under some representative conditions, the numerical method is verified firstly. At the same time, the distributions of the primary aerothermal parameters over the plate surface are provided quantitatively under various attack angles and total pressures. Furthermore, by analyzing the shock wave reflection, interaction and boundary layer separation, the rules of the impact of the control parameters to the flow field and some basic principles in experiments are summarized.

Experimental study on the control of fixed floor boundary layer in low speed wind tunnel

Tang Wei, Chen Li, Wang Hui, Zhang Pingtao

2017, 31(2): 93-97. doi: 10.11729/syltlx20160066

Abstract(192) HTML (220) PDF(15)

Abstract:
In the wind tunnel test of aircraft-taking-and-landing and vehicles, the fixed floor is used to simulate the ground. The existence of the fixed floor boundary layer has an influence on the test data. Generally in order to obtain full and reliable experimental data close to the ground state, various methods can be used to eliminate the boundary layer influence on the surface of the ground floor. Considering the effect and feasibility of large area fixed floor, we have put forward the suction control method of boundary layer thickness in the 8m×6m wind tunnel of China Aerodynamics Research and Development Center. The fixed floor with 48 suction units and 192 suction holes, which can be individually controlled, is developed. Based on the water ring vacuum pipe, a vacuum suction and control system is designed. Through the experiments, 10 kinds of boundary layer thickness control option are analyzed at the wind speed of 70m/s. Then we get the optimal control option with 30mm boundary layer thickness. At this optimal option, the influence on the flow angle is-0.14° and the height of the floor is also investigated. In the end, the suction floor system is applied in the wind tunnel test of C919, where it is found that at the angle of attack more than 8°, the lift coefficient decreases, the drag coefficient increases and the pitching moment increases.

Test technology on unsteady characteristics of inlet flow during fighter plane maneuvers

Wu Chaojun, Nie Bowen, Kong Peng, Lu Xiangyu

2017, 31(2): 98-104. doi: 10.11729/syltlx20160027

Abstract(157) HTML (116) PDF(17)

Abstract:
A test facility was developed in the Φ3.2m wind tunnel, which is driven by two moment electromotors and used to simulate inlet working conditions of the fighter during high maneuvers. The unsteady test method for research on the inlet flow characteristics was established. Based on results of the validating test, the inlet flow characteristics during maneuvers with rapidly changing angle of attack were studied. Some unsteady features, such as the circumferential distortion and turbulence, were obtained from the tests. All these results prove the feasibility of the test technology on studying the unsteady characteristics of the fighter plane inlet flow during maneuvers in the low speed wind tunnel.

2017 Vol. 31, No. 2