实验流体力学

2021, 35(2): 1-4.

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Abstract:

Brief introduction and prospect of calculation methods for one-dimensional characteristics of axial flow compressor

WANG Jin, ZHOU Ling, JI Lucheng

2021, 35(2): 1-12. doi: 10.11729/syltlx20200088

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Abstract:
One-dimensional (1-D) characteristic calculation, as a key link of the compressor design system, plays an important role in the initial design stage of the compressor. As a highly empirical engineering approximate calculation method, one-dimensional performance calculation requires the support of a large amount of experimental data. The quality of the empirical correlation obtained from the experimental data is the key to the success of the one-dimensional calculation. By fully investigating the 1-D performance analysis methods in Europe and the United States, which are mainly based on the stage stacking method and the meanline method, this paper reviews the origin of the 1-D characteristic calculation methods of the axial compressor, and discusses its development trend and research status. In addition, the basic principles of the 1-D characteristic calculation methods and the classic empirical correlations used are summarized, and the direction of future development of 1-D performance analysis of the compressor is pointed out.

Study on two-dimensional control technology of flow field in high-load compressor cascade test

GAO Limin, LIU Zhe, CAI Ming, LI Haoxue

2021, 35(2): 13-21. doi: 10.11729/syltlx20200099

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Abstract:
The boundary-layer attached to the side wall of the linear cascade wind tunnel makes the flow passage contract, which destroys the two-dimensionality characteristic of the cascade flow field. The back pressure gradient of the compressor cascade intensifies the contraction, and the contraction becomes more significant with the increase of load. This paper conducts a numerical study on high-load compressor cascade, studies the factors affecting the two-dimensionality of the cascade blowing experiment and the effect of end wall suction at different axial positions, and explores distributed suction. The results show that the secondary flow at the end wall of the conventional cascade squeezes the main flow, accelerates it, reduces the pressure diffusion, and causes the flow field to be distorted. The total pressure loss deviation is as small as 23%. Front and middle suction can control the two-dimensionality of the cascade as a whole, but the spanwise two-dimensional zone is narrow; the tail suction outlet is wider in the spanwise two-dimensional zone, but it only partially improves the two-dimensionality near the tail edge. The front suction is well controlled at full incidence angle, the middle suction has better negative incidence angle characteristics, and the tail suction flow varies linearly with the angle of incidence. Distributed suction can control the two-dimensionality as a whole and broaden the two-dimensional area, and thus this technique is worth exploring and applying.

Experimental and numerical study of squealer tip flow field considering relative casing motion

DU Jinlin, ZOU Zhengping, HUANG Lin, XUAN Liming, WANG Yuanpeng

2021, 35(2): 22-36, 82. doi: 10.11729/syltlx20200073

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Abstract:
The tip leakage flow is an important factor that causes the internal loss of the aeroengine turbine. The squealer tip can effectively control the tip leakage flow. Accurate understanding of the tip leakage flow structures in the cavity contributes to the understanding of the flow characteristics of the leakage flow and the physical mechanism of the leakage loss. In order to study the change of flow structures in the tip cavity when considering the relative casing motion and the effect on the leakage flow, a low-speed turbine cascade testing facility is built that can model the relative casing motion. The test facility can study factors such as blade profiles, different tip structures, and different incidence angles. A visual testing method of Particle Image Velocimetry (PIV) is proposed to obtain the complex flow structures within the tip cavity. The measurement method developed can obtain the complex flow field and successfully capture the scraping vortex in the tip cavity. In addition, the evolution of the flow structures in the tip cavity is analyzed with the help of numerical results under different casing motion conditions. An aero-labyrinth like sealing effect is formed by the scraping vortex. This sealing effect reduces the equivalent flow area at the gap outlet and diminishes the discharge coefficient of the squealer tip, therefore finally achieving the purpose of controlling the leakage flow. Choosing the appropriate blade load distribution and cavity geometry can improve the clogging effect and expand the control range of the scraping vortex. Mid-loaded blades have a more obvious effect on controlling the leakage flow when using the cavity tip. The tip gap height affects the generation and evolution of the flow structure in the tip cavity by which changes the effect of controlling the leakage flow.

Cascade testing for a subsonic compressor linear cascade and its modification

CAI Ming, GAO Limin, LIU Zhe, LI Haoxue, CHEN Shun

2021, 35(2): 36-42. doi: 10.11729/syltlx20200079

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Abstract:
In order to compare the aerodynamic performance of a compressor airfoil and its modification airfoil with short chord, the linear cascade tests for the baseline and modified airfoils were conducted in a high subsonic cascade wind tunnel. Before the formal experiment, the inflow uniformity and outflow periodicity were checked under the test condition with and without the test cascade, and the measurement blade passage was determined to meet the test requirement. By cascade experiments, the outlet total pressure, outlet flow angle, and the isentropic Mach number distribution on the baseline and modified cascades were obtained and analyzed. The experimental results show that the loss of the modified cascade is larger than that of the baseline, due to the larger adverse pressure gradient after the peak isentropic Mach number position caused by the larger curvature change of the modified cascade. At the design inlet Mach number 0.6, the incidence range with low total pressure loss of the modified cascade is three degrees larger than that of the baseline cascade, and both the baseline and the modified cascades show good loss characteristics under negative incidence condition. At the design incidence angle (i=0°), the wake profile depth of the baseline and modified cascades increases with the inlet Mach number 0.4~0.7. But when the inlet Mach number reaches the critical value of 0.8, both the depth and the width of the wake profile of the baseline and the modified cascades increase.

Effect of bleed on efficiency evaluation of high pressure compressor

CHEN Yunyong, MA Changyou, SUN Zhenyu, CHEN Zhilong

2021, 35(2): 43-49. doi: 10.11729/syltlx20200097

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Abstract:
On the basis of summarizing the differences and correlations between temperature rise efficiency and torque efficiency, two kinds of isentropic efficiency evaluation methods for the high pressure compressor with inter stage bleed are studied in this paper. The influence of inter stage bleed parameters on the two isentropic efficiency corrections is discussed, and the experimental verification is carried out. The results show that: the torque efficiency is always lower than the temperature rise efficiency due to the mechanical transmission loss of the compressor; the temperature rise efficiency of the compressor before and after the correction of the inter stage bleed parameters has no significant difference, and the variation range is within ±0.5%; considering the correction of inter stage bleed parameters, the torque efficiency of the compressor can be significantly reduced, but the relative decrease is not more than the total bleed rate, and the reduction degree is related to the bleed rate and the stage position where the bleed is located; when the inter stage bleed with a large flow rate is conducted at the inlet side of the compressor, the torque efficiency should be corrected, otherwise the torque efficiency may be greater than the temperature rise efficiency.

Experimental research of variable solidity tandem cascade performance

DAI Qiulin, LIU Zhigang, ZHANG Bin, TANG Kai, ZHAO Jiantong, LIU jianpeng

2021, 35(2): 50-57. doi: 10.11729/syltlx20200100

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Abstract:
Experimental research is carried out on a high subsonic tandem cascade, the rear blades of which have two different solidities. For test cascade A, the number of the rear blades is double the amount of B, and there are two locations of rear blades in cascade A, which is following the wake or the mainstream of the front, while the test cascade B only have the rear blades located at the wake of the front. It can be seen from the results that for test cascade A, the load and work capacity of the blades are higher when the rear blades are located near the wake than the mainstream. The larger solidity of rear blades would lead to a blockage in the channel. But cascade B have more uniform outlet flow. Optimizations design should be done about the locations of rear blades and profiles according to the use environment and purpose.

Effect of probe support wake on vibration characteristics of compressor rotor blade

XIANG Honghui, GAO Jie, YANG Rongfei, LIU Haixu, WU Senlin

2021, 35(2): 58-66. doi: 10.11729/syltlx20200070

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Abstract:
In order to understand the abnormal phenomenon of sudden increase of the vibration strain of the first rotor blade in an axial flow compressor experiment, the comparison experiment of the effects of different kinds of inlet measurement probes on vibration characteristics of the rotor blades was conducted. By comparing the variation of the rotor blade vibration signals under different installation layouts of inlet measurement probes, it is verified that the abnormal vibration of the rotor blade is caused by the inlet measurement probes. The flow mechanism of the probe support wake inducing the resonance of rotor blade was also analyzed using the fluid-structure coupling numerical simulation method. The investigation results show that the first order resonance of the rotor blade of the axial flow compressor emerges under an engine order excitation condition, which is induced by the cylindrical probe support with the diameter of 10 mm. As the size of the probe support decreases, the level of the rotor blade vibration response is reduced evidently. The disturbance frequency of the probe-support-induced-compressor-rotor-blade-resonance originates from the combined effect of the wake induction frequency and the passing frequency of the probe support. The shedding vortex of the probe support wake can cause large amplitude fluctuation of the inlet attack angle of the rotor blade.

Experimental research on the effect of processing technology of cascade test article on the performance measurement

WANG Hui, TANG Kai, DAI Qiulin, LIU Zhigang, LING Daijun

2021, 35(2): 67-74. doi: 10.11729/syltlx20200087

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Abstract:
In order to solve the processing problems of the test article occurred in the cascade experimental research, investigation and study of the processing technologies of the test blade and Aero-Plexiglass sidewall have been carried out through processing test and experimental validation. And then the detection methods of the key parameters are put forward based on trilinear coordinates measuring instrument. It can be seen from the results that considering the processing cost and the effects of the blade surface roughness on the cascade performance, the suitable surface roughness of the blade for high speed and high load cascade is suggested to be not more than Ra=1.6. Stress lines and black areas may appear on the Aero-Plexiglass sidewall due to some factors, such as material selections, manufacturing procedures, processing technologies and improper assembly or use, etc., which would cause adverse effect on schlieren visual measurement in high speed state. The processing quality of the test article is greatly improved by developing the detection methods of the key parameters, which will be helpful to get more accurate and reliable performance data.

Simulation and analysis of simultaneous 3D velocity and temperature measurement technique based on light field imaging technology

WU Taofeng, LUAN Yinsen, SHI Shengxian

2021, 35(2): 75-82. doi: 10.11729/syltlx20200092

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Abstract:
A technique that can simultaneously measure three-dimensional velocity and temperature is proposed. The technique is based on LF-PIV(Single-camera Light-Filed Particle Image Velocimetry), and the temperature measurement technology making use of the lifetime of temperature-sensitive phosphorescent particles. The correspondence between the lifetime and temperature of the particle(Mg₃F₂GeO₄: Mn)was experimentally calibrated, and synthetic light-field particle image simulation was performed to study the effect of camera exposure time characteristics on measurement accuracy. Under the condition that the exposure time of the two frames of camera is controllable, the water jet data obtained by DNS (Direct Numerical Simulation) are used for digital synthetic image simulation (the jet temperature and ambient temperature are 343.15 K uniformly). The three-dimensional particle image was reconstructed, temperature and velocity fields were calculated, and measurement errors were analyzed. In addition, a theoretical analysis and simulation study of the measurable velocity range was carried out under the existing light field camera hardware parameters. Simulation results show that, under the condition of controllable exposure time of two frames of camera, the new technique can simultaneously measure the three-dimensional velocity and temperature; however, the measur-able velocity is limited by existing light field camera hardware parameters.

Experimental study on drag reduction of L-shaped bluff body by AC-DBD plasma actuation

LAN Ziqi, SHI Zhiwei, SUN Qijie, GENG Xi

2021, 35(2): 83-91. doi: 10.11729/syltlx20200095

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Abstract:
Plasma flow control is a widely used active flow control method. In order to further expand the application scope and understand the actuation mechanism, three kinds of AC-DBD (Dielectric Barrier Discharge) plasma actuator layout forms are used to compare the drag reduction capabilities of the L-shaped model after actuation, and the drag reduction mechanism is studied. The experiment is carried out in a low-speed DC wind tunnel, with a wind direction angle of 0°, and a wind speed of 2-8 m/s. These different actuators layout forms are the plasma actuator placed close to the leading edge along the incoming flow direction, the plasma actuator placed close to the leading edge against the incoming flow direction, and the plasma actuator arranged at the corner, respectively. Research shows that plasma actuators under different wind speed conditions have a certain control effect on drag reduction of bluff bodies, and the control ability decreases with the increase of wind speed. The plasma actuator placed in the corner produces the best control effect, and the drag reduction rate can reach more than 13% at low speed. The plasma actuator placed close to the leading edge against the incoming flow direction produces a similar effect. The drag reduction rate of the plasma actuator near the leading edge along the inflow direction can only reach about 7% at most. By analyzing the flow field, it is shown that the change of layout position produces different disturbance effects. Different flow control mechan-isms are the key factors affecting the actuation effect.

Wind field measurement over complex landforms based on Multi-rotor Unmanned Aircraft

WU Honghua, ZHANG Liang, Feng Hao, HU Haohui, LI Zhengnong

2021, 35(2): 92-103. doi: 10.11729/syltlx20200055

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Abstract:
The purpose of this study is to explore the method of measuring planar wind field over different landforms based on Multi-rotor Unmanned Aircraft (MUA) equipped with a wind speed and direction measurement device. In this study, a wind tower of a test base in Yanqing, Beijing is used as a reference. Firstly, the accuracy of MUA wind measurement is studied. Then, the wind speed and direction measured by MUA at different measuring points and the wind tower in the same period are taken for orthogonal decomposition to obtain the ratio of wind speed and turbulence between MUA and the wind tower. Through the data of the wind tower and the ratio, the wind speed and direction of different positions are deduced, and the wind field over the complex landform is obtained. The results show that the error of MUA average wind speed and average wind direction after correction is smaller. The turbulence measured by MUA is larger than that measured by the wind tower, and the turbulence measured by MUA can be reduced partly by the moving average method. The wind field conditions are greatly affected by the landforms, and the wind field over complex landforms fluctuate more frequently. The study verifies the feasibility of using MUA equipped with an anemometer to measure the planar wind field over different landforms, which can provide reference ideas and methods for wind field measurement in a local area and micrositing of wind farms.

Advances in experimental research on Taylor-Couette flow characteristics and drag reduction

ZHANG Wenyun, HU Haibao, WEN Jun, CAO Gang, REN Liuzhen

2021, 35(2): 104-111. doi: 10.11729/syltlx20190163

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Abstract:
The coaxial rotor filled with fluid in the gap can be simplified to be the Taylor-Couette flow model. It has the characteristics of simple structure, high symmetry, and easy to carry out high-precision experimental tests, and is widely used to study basic fluid mechanics problems. Rotary shaft structures involving Taylor-Couette flow are ubiquitous in the engineering field, and research related to Taylor-Couette flow characteristics and drag reduction methods has important economic value in the engineering field. In order to facilitate researchers to understand the experimental progress of Taylor-Couette flow characteristics and drag reduction, this paper systematically introduces the main dimensionless influence parameters, flow field structure and torque characteristics of Taylor-Couette flow. According to the differences in drag reduction mechanisms, the drag reduction methods can be divided into two categories: the general and the specific drag reduction method. Finally, the prospect of the research on Taylor-Couette flow drag reduction is given, which provides reference for future research work.

Wall effects and cavitation number correcting of supercavitating tests in water tunnel

CHEN Weizheng, WEI Xizhong, LI Peng

2021, 35(2): 112-116. doi: 10.11729/syltlx20200007

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Abstract:
This paper is intended to evaluate the wall effects in the super-cavity flow past a test model held in a closed water tunnel, and to establish a theoretical correction rule. Based on the principle of independence of cavity expansion, mainly considering the longitudinal pressure gradient in the working section, a theoretical solution of the super-cavity shape in the closed water tunnel is derived. With the theoretical solution the wall effects are discussed, and a correction rule of the cavitation number is presented.

2021 Vol. 35, No. 2