实验流体力学

2021年3期目录

2021, 35(3): .

Abstract(208) PDF(33)

Abstract:

2020年优秀论文和优秀审稿专家

2021, 35(3): 1-1.

Abstract(179) PDF(20)

Abstract:

Icing and anti-icing test technology of aero-engine based on large-scale icing wind tunnel

LAI Qingren, LIU Qinglin, GUO Long, ZHANG Pingtao, YI Xian

2021, 35(3): 1-8. doi: 10.11729/syltlx20200067

Abstract(872) HTML (464) PDF(75)

Abstract:
The icing and anti-icing process of the aero-engine is complex, which can not be simulated accurately by numerical calculation. As a result, experiment is an indispensable means for the engine research. The first large-scale icing wind tunnel of our country has been built, which has the capacity to carry out icing tests on the aircraft wing section. But further development of the icing and anti-icing test technology is needed to meet the requirement of the next stage model designing and airworthiness certification for aero-engines in our country. Supported by the 3 m×2 m large-scale icing wind tunnel, the inlet gas simulation technology and hot-air supply technology were developed first, then a set of test procedures and methods was put forward, and finally the icing wind tunnel test for the inlet part of an aero-engine was carried out. The results indicate that the system can simulate the internal and external flow coupling of the engine and the anti-icing state of the compressor. The procedures and method of icing wind tunnel test are reasonable and feasible, and the test dynamic process and the flow field pressure in the inlet are successfully measured. It provides a technical support for the design of ice protection system and the verification of airworthiness on aero-engines.

Experimental analysis on aero-loading of wing skin with icing accretion

LI Zhao, YANG Guangjun, JIANG Feng

2021, 35(3): 9-15. doi: 10.11729/syltlx20200074

Abstract(420) HTML (145) PDF(26)

Abstract:
Ice accretion changes the aerodynamic shape and flow field of the airfoil, which makes the aerodynamic load distribution of the wing change dynamically. The skin, as the object of bearing and transferring aero-loading, produces different vibration responses under its dynamic action. Taking a large camber and thick airfoil as an object, the vibration characteristics of the upper and lower skins of the trailing edge under the typical icing condition are extracted, the load spectrum is used to study the skin vibration and flow field changes, and the structural stability of different skin is investigated. The results show that: Different skins have different load sensing performance for the ice-induced detached vortices and trailing edge separated vortices; the load spectrum and energy are relatively concentrated for the rigid skin while scattered for the flexible skin; as the ice accretes, the dominant frequency of detached vortices decreases slightly, substrate ice causes wide-width and high-frequency vibration, and the mixing of detached vortices and the wake results in the increase of the loading energy around the trailing edge.

Prediction of ice shape characteristic parameters based on BP nerual network

CHAI Congcong, YI Xian, GUO Lei, WANG Jun

2021, 35(3): 16-21. doi: 10.11729/syltlx20200016

Abstract(502) HTML (203) PDF(38)

Abstract:
Airfoil icing affects the aerodynamic characteristics of aircraft flight, which can lead to accidents when it is serious. The prediction of ice shape parameters can effectively prevent accidents. In this paper, BP neural network is used to establish the prediction model of airfoil ice shape characteristic parameters, and k-fold cross validation is used to select the network structure, in which the meteorological and flight conditions are the inputs, and ice shape characteristic parameters such as the ice limit, the ice angle height and angle are the outputs. The experimental results show that the relative error between the predicted ice shape parameters (except for the height of the lower ice angle) and the numerical results is less than 5%, which proves that the method has a good prediction ability.

Preliminary research on size measurement of supercooled large droplet in icing wind tunnel

CHEN Shuyue, GUO Xiangdong, WANG Zixu, LIU senyun, WU Yingchun

2021, 35(3): 22-29. doi: 10.11729/syltlx20200104

Abstract(578) HTML (214) PDF(35)

Abstract:
Drop-size measurement of the supercooled large droplet (SLD) is very important for capacity building of the icing wind tunnel. In order to evaluate the capability of Phase Doppler Interferometer Flight Probe Dual Range (PDI-FPDR) in measuring the diameter of SLD, the standard droplet stream generated by a droplet generator, was used to evaluate the uncertainty of PDI-FPDR for drop size measurement. Then, for the real large-droplet spray, the particle size characteristic parameters were measured by Malvern and PDI-FPDR simultaneously. The large-droplet spray measurement capability of PDI-FPDR has been further evaluated. The results show that the small size range channel of PDI-FPDR can't accurately measure large droplets, and its measurement results are much smaller than the real droplet size. The relative error of measuring a 189.0 μm droplet is -72.8%. The measuring accuracy of the large size range channel is high, but the precision is poor. The relative error of measuring a 240.5 μm droplet is -5.1%, and the maximum deviation is 50.2 μm. For typical large-droplet spray, the PDI-FPDR small size range channel has poor applicability under measuring conditions of median volume diameter (MVD) greater than 75.0 μm. The measured MVD values of PDI-FPDR large size range channel are larger than those of Malvern.

Review of the cascade experimental technology

LING Daijun, DAI Qiulin, ZHU Rongchuan, WANG Hui, ZHAO Jiantong

2021, 35(3): 30-38. doi: 10.11729/syltlx20200102

Abstract(1416) HTML (336) PDF(161)

Abstract:
Profile design is the basis of modern aero engine and gas turbine aerodynamic and thermodynamic research. As an economic tool, cascade test can be used to explore the profile design method and verify the engineering design in a short time. It plays an important role in the modern compressor and turbine aerodynamic design. The simulation of experimental environment and state is the key of cascade experiment. With the development of the profile design technology and the improvement of cascade performance, profile tests should be expanded and improved to get the variation rules of the profile total performance more accurately and reliably, such as the flow periodicity control, Axial velocity density ratio, 3D effect, low Reynolds number, unsteady flow etc., which would lay the foundation for the research of flow mechanism and flow characteristics that leads to performance change. The history of cascade experimental technology development is introduced in this paper, and the recent research orientations and hotpots are analyzed to provide a reference for relevant studies.

PIV experimental study on flow characteristics of a low swirl number precessing jet

FU Hao, HE Chuangxin, LIU Yingzheng

2021, 35(3): 39-45. doi: 10.11729/syltlx20200129

Abstract(545) HTML (175) PDF(62)

Abstract:
This study focuses on the flow characteristics of a low swirl number precessing jet at Reynolds number Re=4.5×10⁴ using particle image velocimetry (PIV). The time-averaged streamwise velocity fields, streamwise velocity fluctuation intensity fields and time-averaged vorticity fields at three swirl numbers, i.e., S=0, 0.26 and 0.41, respectively, are compared and analyzed. The experimental results show that as the swirl number increases, the attenuation of the streamwise velocity and its fluctuation intensity increase along the streamwsie direction, the velocity fluctuation intensity on the jet centerline increases, the recirculation zones caused by the confinement move upstream with their scales decreasing, and the streamwise development of the vortex in the outer shear layer decays rapidly, while that in the inner shear layer is almost unaffected. In addition, combining the streamwise velocity spectrum and the characteristics of the transient flow field at a typical time, it can be seen that as the swirl number increases, the precession frequency increases, and the starting position of the precession phenomenon moves upstream, which increases the precession deflection angle.

Experimental investigations on the separation interference characteristics of supersonic internal weapon releasing from the aircraft

DONG Jingang, ZHANG Chenkai, XIE Feng, QIN Yongming, MA Handong

2021, 35(3): 46-51. doi: 10.11729/syltlx20200080

Abstract(515) HTML (183) PDF(53)

Abstract:
The internal weapon is subject to the complex interference flow field of the aircraft during the separation of supersonic bombs, and its aerodynamic characteristics are significantly different from the freestream conditions, which will have a certain impact on the safety of the bomb separation. Using the new CTS test technology based on the configuration of the parallel mechanism and the schlieren techniques, the interference characteristics of a new aircraft with a typical bomber layout and a typical air-to-air missile model were studied. Under the influence factors such as the separation altitudes and folded/unfolded rudder, the pitching motion characteristics of the missile and the interference of the flow field structures for the aircraft are compared. Results show that at supersonic speed, there exists a complex shock system structure for typical embedded bomber fighter configuration, which will have a strong aerodynamic interference effect on the carrier bomb, inducing the carrier to nose up. With no initial separating angular velocity, unsafe separation is tend to occur. When reducing separation altitude, unsafe separation tendency for the bomb would advance. During the separation process, the rudder surface is not conducive to the attitude control of the loaded bomb. Meanwhile, folded rudder is unfavorable for the attitude control of the bomb during the separation procedure, thus folding the rudder as soon as possible is demanded at the premise of safe separation, in order to guarantee stability control of the bomb attitude.

An experimental study on drag reduction of superhydrophobic rotating disk with air plastron

CHEN Zhengyun, ZHANG Qingfu, PAN Chong, LIU Yanpeng, CAI Chujiang

2021, 35(3): 52-59. doi: 10.11729/syltlx20200025

Abstract(613) HTML (273) PDF(45)

Abstract:
Drag reduction performance of superhydrophobic disks in a Von Kármán swirling flow with Re~O(10⁵) was experimentally studied. Two superhydrophobic disks, which have different microstructures, i.e., one with micron-scale homogeneous roughness (abbreviated as SHS#1) and the other with additional millimeter-scale nonhomogeneous grid pattern (abbreviated as SHS#2), have been tested. Both SHS#1 and SHS#2 are prepared by the method of physically spraying nano-scale hydrophobic particles onto an acrylic-plate substrate. The grid pattern on SHS#2 is obtained by applying a mask of wire mesh during the spraying procedure. The mean skin-friction drag on the rotating disk was measured by a torquemeter. It is shown that for the superhydrophobic surface to reduce drag in Von Kármán swirling flow, there is a critical Reynolds number Re_c. When Re < Re_c, the superhydrophobic surface has a stable long-term drag reduction effect, with drag reduction ratio up to 30%; but when Re>Re_c, the drag reduction effect is rapidly lost with the increase of Re. Compared to SHS#1, SHS#2 can effectively improve the dynamic stability of the air plastron attached on the surface. Additionally, the air plastron on the superhydrophobic surface can be effectively restored by pulse air injection, and so can the drag reduction effect. This observation indicates a promising strategy for reliable and sustainable drag reduction via superhydrophobic surface.

Numerical simulation and experimental measurement of fluid flow field in pipe with capsule robot

LIANG Liang, TANG Puhua, LIU Yu

2021, 35(3): 60-68. doi: 10.11729/syltlx20200145

Abstract(382) HTML (218) PDF(19)

Abstract:
Capsule robots are widely used in the inspection and treatment of human intestines. According to the permanent magnet method, a magnetically controlled smooth capsule robot is designed and manufactured. Based on the Computational Fluid Dynamics (CFD) method, the fluid flow field (velocity and vorticity) around the capsule robot is numerically simulated when the capsule robot precesses (rotates and translates) in the pipe filled with mucus. The Particle Image Velocimetry (PIV) technology is used to measure the fluid flow field. The resistance, the resisting moment of the robot and the average turbulent intensity of the surrounding fluid are further calculated as the capsule robot precesses at different rotational speeds. Finally, the shape and distribution of fluid streamlines, and the distribution and size of the fluid velocity and vorticity around the capsule robot are also experimentally measured. The results show that: 1) when the rotational speed of the capsule robot is increased, the fluid velocity and vorticity in the surrounding and lower regions of the capsule robot are slightly increased, while the fluid streamlines and vorticity distribution of the surrounding fluid are basically similar. 2) With the increase of the rotational speed of the capsule robot, the resisting moment of the capsule robot in the forward direction and the average turbulent intensity of the surrounding fluid are all increased, while the resistance of the capsule robot in the forward direction remains basically unchanged. 3) The experimentally measured shape and distribution of fluid streamlines, and the measured distribution and size of the fluid velocity and fluid vorticity around the capsule robot are basically similar to the numerical calculation results.

A study of a wide range (1-600 kPa) static calibration method for pressure sensitive paints

ZHU Yong, DONG Zhe, PENG Di, LIU Yingzheng

2021, 35(3): 69-76. doi: 10.11729/syltlx20200138

Abstract(444) HTML (133) PDF(45)

Abstract:
Pressure sensitive paint is an advanced optical testing technology. The calibration error of paint is one of the main error sources of this technology. The measuring range of pressure sensitive paint is gradually expanding from the conventional pressure range to ultra-low pressure and ultra-high pressure. Therefore, it is necessary to develop a calibration system with a large pressure adjustment range and high precision. A new PSP wide range pressure calibration method and system are proposed by combining the existing method of variable pressure with the method of variable concentration. The performance difference between this system and ISSI's commercial calibration system is studied by theoretical calculation. The results show that the calibration error of the PSP wide range pressure calibration system in the low-pressure area (1-20 kPa) can be controlled within 0.5 kPa, and its performance is better than that of the ISSI calibration system. In the medium-pressure area (20-200 kPa), the error of this system is under 4%, which is close to that of the ISSI calibration system, and the error decreases with the increase of pressure. In the high-pressure area (200-600 kPa), it has a broader calibration range and can realize the calibration of PSP in an ultra-high-pressure environment (400-600 kPa). This paper also carried out calibration tests on the two most commonly used quick response PSPs. The results show that proposed system has high calibration accuracy and can realize the wide range calibration of PSP.

Research on large field visualizaiton based on divergent light reflective layout

YUE Maoxiong, ZHANG Wanzhou, WU Yungang, YUAN Qiang, DENG Weixin

2021, 35(3): 77-82. doi: 10.11729/syltlx20200081

Abstract(317) HTML (150) PDF(24)

Abstract:
Larger scale of flow-field visualization is required for larger wind tunnel, larger test model and longer jet flow. Two methods of the large field visualization were proposed which are based on divergent light reflective layout and are named as the reflective focusing schlieren method and the reflective shadow method, respectively. A reflective focusing schlieren device was built in laboratory which improves the source grid and light source. A visualization field with a diameter of about 1.5 m was obtained. The field uniformity and the minimum exposure time under test condition indicate that the reflective focusing schlieren method could be utilized for the large scale wind tunnel and other situations. Also, to realize the large field visualization for the situation with strong vibration, a diffuse reflective shadow visualization device was set up, and a visualization field with a length of about 2.5 m was obtained for a combustion jet flow. Finally, according to the characteristics of the reflective method, the applicability of the method in larger tunnel layout was evaluated, and the results show that the method is completely suitable for the large-scale wind tunnel visualization.

Research on density variation and control method of high temperature fuel in combustor

WANG Xiangyi, ZHANG Lei, ZHANG Ruoling, JIANG Jin

2021, 35(3): 83-87. doi: 10.11729/syltlx20190162

Abstract(490) HTML (149) PDF(18)

Abstract:
The operating characteristics of the high temperature fuel in the active cooling channel and the variation of the fuel density are analyzed. The design methods of the fuel temperature and pressure measurement system are given, and the control scheme of the injection pressure which can adapt to the great change of the fuel density is designed using the balance equations of fuel energy and entropy. In order to determine the influence of the fuel density change on the control scheme, the fuel injection pressure control tests are carried out on the directly connected combustion test platform. Both the fuel measurement and control systems work normally during the test, and the processes of the fuel injection pressure and the density variation agree well with the prediction, which verifies the effectiveness of the high temperature fuel measurement, control method and the fuel density calculation method.

Particle reconstruction of volumetric particle image velocimetry with strategy of machine learning

ZHU Haoran, GAO Qi, WANG Hongping, LIAO Xiangwei, ZHAO Liang, WEI Runjie, WANG Jinjun

2021, 35(3): 88-93. doi: 10.11729/syltlx20200141

Abstract(825) HTML (259) PDF(118)

Abstract:
Three-dimensional particle reconstruction with limited two-dimensional projections is an underdetermined inverse problem that the exact solution is often difficult to be obtained. In general, approximate solutions can be obtained by optimization methods. In order to obtain a better quality particle field for Tomographic PIV, in the current work, a practical particle reconstruction method based on convolutional neural network (CNN) is proposed. The proposed technique can refine the particle reconstruction from a very coarse initial guess of particle distribution from any traditional algebraic reconstruction technique (ART) based methods. Compared with available ART-based algorithms, the novel technique makes significant improvements in terms of reconstruction quality. It can effectively eliminate ghost particles and restore the shape of particles more accurately, and is at least an order of magnitude faster with dense particle concentration.

Development of a two degrees of freedom support system for full model gust tests

TANG Jianping, WU Fuzhang, PU Lidong, ZENG Xian'ang, ZHANG Haiyou, ZHANG Lei

2021, 35(3): 94-99. doi: 10.11729/syltlx20200062

Abstract(462) HTML (248) PDF(26)

Abstract:
This paper describes the development of a support system for free flying dynamically scaled full model. The free flying model requires plunge and pitch degrees of freedom(DOF) for the measurement of the gust response in the 8 m×6 m wind tunnel in LSAI of CARDC. The main part of the system consists of 2 slideways and a steel beam. The characteristics of the system include: its left and right structures are symmetrical, the range of free movement in the plunge direction is 2.8 m and the coefficient of friction is 0.006, the range of free movement in the pitch direction is ±10°, the lowest frequency of the system supporting a 50 kg model is not less than 12 Hz, and the structure changes in the test section can be ignored. By optimizing the structure and selecting the materials, the sliding carriage's mass is less than 6 kg. A gust load alleviation test for a full model was successfully completed by the use of the support system, which verifies the practical effect of the system.

2021 Vol. 35, No. 3