实验流体力学

2016, 30(3): 1-1.

Abstract(99) PDF(9)

Abstract:

Analysis of water droplets distribution in the test section of an icing wind tunnel

Yi Xian, Guo Long, Fu Cheng, Zhang Haiyang, Zhou Zhihong, Peng Qiang

2016, 30(3): 2-7. doi: 10.11729/syltlx20160034

Abstract(258) PDF(14)

Abstract:
The spray system is the main component of an icing wind tunnel.It costs a lot to measure water droplets characteristics directly in the test section of an icing wind tunnel.In this paper,a means,including both experimental and numerical method,of studying the droplet dis-tribution in the icing wind tunnel test section is proposed.The droplet distribution characteristics at the nozzle exit are obtained by setting up an independent experimental system based on which the numerical method is used to calculate the movement and mass/heat transfer process of differ-ent droplets in the wind tunnel.Then the diameter and mass fraction of different droplets after e-vaporation can be obtained.The distribution characteristics of droplets in an icing wind tunnel with 3m×2m test section under typical conditions are investigated,and the effects of air humidi-ty is explored.The results show that:(1)the droplets at the nozzle exit and in the test section are in an approximate normal distribution,the MVD in the test section is close to the initial value at the nozzle exit,and evaporation does not cause a significant change in MVD.(2 )generally speaking,the smaller the absolute humidity is,the greater the evaporation of water droplets is. Though,when the absolute humidity is 100%,the MVD of droplets in the test section is smaller than that when the humidity is 70%.The research results can provide a good technical basis for the design and use of an icing wind tunnel.

Ice shape correction method based on the error of cloud parameters

Zhou Zhihong, Yi Xian, Guo Long, Gui Yewei, Che Jing

2016, 30(3): 8-13. doi: 10.11729/syltlx20160031

Abstract(146) PDF(10)

Abstract:
Precise control of icing wind tunnel cloud parameters and the accuracy of measured parameters are two technical problems of icing wind tunnel experiments.They affect the accuracy of the experiment and bring errors to results.To solve the problems,this paper proposes an ice shape correction method based on cloud parameters.The key element of the ice shape correction is analyzed with the aerodynamic point of view,and the relationship between the cloud parame-ters and the typical geometric characteristic parameters of the ice is simulated by using artificial neural network technology.A TFI ice shape correction method is established.The NACA0012 airfoil is selected as the research obj ect.The ice shape has been corrected to account for the error caused by the cloud parameters of liquid water content and droplet diameter.The method has sig-nificantly improved the agreement between the corrected ice shape and the target shape.It is thus verified that our method is correct and it can be used for icing wind tunnel test.

Ice cross sectional profile measurement based on line structured light

Wang Bin, Liu Guihua, Zhang Liping, Long Huimin, Gai Wen

2016, 30(3): 14-20. doi: 10.11729/syltlx20160040

Abstract(159) PDF(6)

Abstract:
To realize the ice cross sectional profile measurement in a non-contact way,a line structured light based measurement is adopted.Firstly a laser sheet is proj ected vertically on the ice surface.Secondly,the image of the deformed laser line on the ice surface is captured by a camera.Finally,the 3D coordinates of the laser line on the ice surface are calculated upon the cal-ibrated geometric relationship between the laser sheet and the camera.Then the proj ection of these 3D coordinates on the laser sheet is the ice cross sectional profile.In this paper,a simple line structured light measurement device and a measurement procedure are developed.To deal with the problem of the low image contrast due to the low reflected laser energy on ice,a novel laser line center extraction method is provided.In the experiments,an ice sheet frozen by a re-frigerator with its radius known is measured.The maximum relative error is 0.052,and the mean relative error is 0.018.A preliminary measurement result of the icing on two elements air-foil generated in an icing wind tunnel is also obtained.It lays a technical foundation for the 3D ice shape online measurement during ice accretion in icing wind tunnels in the future.

Experimental study on temperature effecton deformation and drag characteristics of supercooled large droplet

Wang Qiao, Xiao Jingping, Liu Senyun, Xiao chunhua

2016, 30(3): 21-26. doi: 10.11729/syltlx20160028

Abstract(180) PDF(5)

Abstract:
In order to explore the influence of temperature on the dynamic characteristics of the supercooled large droplet (SLD),SLD dynamics experiments were conducted in room tem-perature and low-temperature environments.Studies have shown that:when a supercooled large droplet is moving in a rapidly accelerated stream,the changing history of the drop’s deformation characteristics and drag characteristics with the variation of the We number can be divided into three stages:fluctuation stage,step stage and smooth stage,and it is subj ected to the influence of the low-temperature environment.The deformation rate and drag coefficient of the droplet with the same We number decrease with decreasing temperature.In the fluctuation phase,tem-perature has the largest influence on SLD dynamic characteristics,but the temperature effect weakens in the step and smooth stage.

An experimental investigation on the process of droplet icing/frosting and defrosting/deicing using dual synthetic j et

Li Yuj ie, Luo Zhenbin

2016, 30(3): 27-32. doi: 10.11729/syltlx20160004

Abstract(288) PDF(10)

Abstract:
The processes of a droplet icing/frosting and defrosting/deicing using a dual syn-thetic jet actuator (DSJA)was experimentally studied.The temperature of a semiconductor-cooled board was reduced to -30℃,and the DSJA was started after the droplet was frozen.The processes of the droplet icing,frosting,defrosting and deicing were observed by an electron micro-scope.The experimental results show that the structure of the frost changes quickly from needle to column,and then to granule.Meanwhile,the thickness of the frost attenuates.Later on,be-cause the DSJ can enhance the heat transfer,the cone of the frozen droplet becomes flattish and the height of the frozen droplet decreases slowly.The thawed water flows downwards and freezes again.The interface area between the frozen droplet and the semiconductor-cooled board is in-creased.

Research progress on supercooled large droplet icing detection technology

Zhang Hong, Zhang Wenqian, Zheng Ying

2016, 30(3): 33-39. doi: 10.11729/syltlx20160037

Abstract(249) PDF(16)

Abstract:
The Supercooled Large Droplet(SLD)icing is a new problem that emerged in recent years.The ice detection technology of SLD,which restricts the overall development of the air-craft icing protection system,is a key technology for securing the aircraft flight safety.The arti-cles published recently on SLD ice detection are summarized and discussed.The new problems of the ice detection technology when applyied to SLD are presented from the perspectives of the icing mechanism and the detection principle.The new requirements of the SLD icing detection technol-ogy are summarized through the analysis of the latest airworthiness specification.According to the technology maturity,the SLD icing detection technologies are introduced in detail.A new classification method for the probe type SLD icing detector is firstly reported including droplet traj ectory detection and back-flow characteristics detection.

Experimental research on ethylene ignition and flame propagation processes for scramj et at Ma4

Zhang Wanzhou, Le Jialing, Yang Shunhua, Cheng Wenming, Deng Weixin

2016, 30(3): 40-46,84. doi: 10.11729/syltlx20150161

Abstract(169) PDF(6)

Abstract:
Gaseous ethylene ignition experiments were carried out on directly-connected pulse combustion facility.The stagnation temperature and the Mach number at the isolator entrance were 935K and 2 respectively,which simulated the flight with Mach number 4.Ethylene was ig-nited successfully and stable combustion was maintained by employing torch igniter and pilot hy-drogen.Wall pressure measurement,high speed imaging and numerical simulation were em-ployed to analyze the ignition and flame propagation processes.The results indicate that:(1)the recirculation zone in the cavity avails ignition,while the shear layer and the rear of the cavity are the main regions for stable combustion;(2)after ignition,the density of the fuel and oxidizer is the key factor to stable combustion,and oxidizer that continually entering the shear layer and rear of cavity supports the stable combustion;(3 )combustion downstream of the cavity pro-motes the pressure level in the combustor,and the unstable combustion there causes pressure os-cillation.The high velocity and variation of oxygen content are the two main factors including un-stable combustion downstream of the cavity.

Investigation on full-coverage film cooling effectiveness of turbine vane with exit Mach number from 0.81 to 1.01

Zhang Hong, Li Jie, Tian Shuqing

2016, 30(3): 47-52. doi: 10.11729/syltlx20150095

Abstract(128) PDF(3)

Abstract:
Heat transfer coefficient and film cooling effectiveness are investigated on a turbine vane employing the transient thermal couple technique.There are 1 3 rows of film cooling holes placed on the test blade.The cooling gas through film holes is supplied by two plenums,with mass flow ratio of 5.06% in the first plenum and 1.14% in the second.To match the real engine operating condition,the range of the inlet Reynolds number and the exit Mach number of the cur-rent experiment are 1.7×105~5.7×105 and 0.81~1.01,respectively.Heat transfer coefficient distribution is obtained,and effects of Reynolds number and Mach number to film cooling effec-tiveness distribution are investigated.The results show that heat transfer coefficient and film cooling effectiveness are higher in the near hole region.Film cooling effectiveness increases as in-let Reynolds number increases,especially on the pressure side and suction side,while the effect of exit Mach number to film cooling effectiveness is not obvious.

Experimental investigation on separation flow control of backward facing step with synthetic j et

Li Binbin, Yao Yong, Gu Yunsong, Cheng Keming

2016, 30(3): 53-60. doi: 10.11729/syltlx20150137

Abstract(174) PDF(12)

Abstract:
Backward facing step flow with boundary layer separation and reattachment is a common phenomenon in engineering.The research of backward facing step flow has important theoretical significance and practical value.Backward facing step flow contains a variety of com-plex fluid mechanics,such as flow transition,flow separation,reattachment and unsteady flow. It has important academic significance in the field of fluid mechanics.The test techniques of sur-face pressure and particle image velocimetry have been applied to investigate the backward facing step turbulent separated flow control with synthetic j et.Through analysis of the pressure coeffi-cient distributions of the step wall surface,transient vortex flow structure and time-averaged flow structure,it reveals the separation flow control mechanism of synthetic j et on the backward facing step reattachment length and recirculation zone.The results show that the synthetic j et imposed on the leading edge can effectively reduce the range of the recirculation zone,the vortex structure of which is locked by the synthetic j et perturbation.In this experiment,the greater the momentum coefficient of the synthetic j et is,the better the control effect becomes.The time-av-eraged effect is:when the momentum coefficient of the synthetic jet is 0.771%,the reattachment length can be decreased by 50%.

Investigation of the unsteady aerodynamic characteristics of a fighter with complex configuration undergoing yaw-roll coupling oscillation motion

Yang Wen, Bu Chen, Sui Jianj un

2016, 30(3): 61-65. doi: 10.11729/syltlx20150104

Abstract(129) PDF(4)

Abstract:
A new set of double degree of freedom in volatile test system is designed and con-structed in FL-8 wind tunnel.The test apparatus can not only simulate aircraft′s single degree of freedom maneuver,but also realize yaw-roll coupling movement and pitch-roll coupling move-ment around the body axis.This paper introduces the experimental proj ect in detail and conducts research into the time history influence when the model is maneuvering.Afterwards the influence of the coupling factor on the unsteady aerodynamic characteristics undergoing yaw-roll coupling oscillation motion is analyzed quantitatively at the oscillation equilibrium position.The results in-dicate that the unsteady aerodynamic gained undergoing yaw-roll coupling oscillation motion is e-qual to the linear superposition of the unsteady aerodynamic gained in the test of single yaw and roll motions when the angle of attack at the equilibrium position is less than the stall angle of at-tack.The influence of the coupling factor on the unsteady aerodynamic is remarkable near the stall angle of attack.The influence of the coupling factor on the unsteady aerodynamic is weak when the angle of attack at the equilibrium position is much greater than the stall angle of attack.

Control of cavity flow pressure oscillation through leading edge boundary layer perturbation

Tao Yang, Wu Jifei, Xu Laiwu, Jiang Weimin

2016, 30(3): 66-70. doi: 10.11729/syltlx20150103

Abstract(121) PDF(7)

Abstract:
Weapons embedding is the key technique to achieve the advanced aerodynamic char-acteristics and stealthy performance for the supersonic cruising fighter.The flow in the weapon cabin is very complex and the sound pressure level of strong noise induced by strong fluctuant pressure is as high as 170dB which may damage the cabin’s structure and the interior facilities,so the cavity noise generation and its corresponding suppression become the hot research topics. This paper presents a brief analysis of the aero acoustic characteristics in a cavity of length-depth ratio (L/D)of 4 with and without leading edge ramps under sub-and transonic conditions (Mach number is 0.6、0.95 and 1.2).The suppression effects of the ramp on aerodynamic noise are dis-cussed by analyzing the sound pressure level distribution on the centerline of the cavity floor and the sound pressure frequency spectrum (SPFS)characteristics at different measurement points. The results show that the leading edge ramps can suppress aerodynamic noise inside the cavity both at the floor and at the sidepiece and it is more effective in SPL reduction in the rear range of the cavity than in the front.The energy peaks of SPFS at some measurement points almost disap-peared with the leading edge ramps which indicate that the flow mechanism of self-sustained os-cillation disappeared.

Combined flame radiation and cross-correlation method for velocity measurement of burning particles

Jiang Yongjun, Yang Bin, He Yuan, Zhou Wu, Cai Xiaoshu

2016, 30(3): 71-75. doi: 10.11729/syltlx20150106

Abstract(249) PDF(3)

Abstract:
For online velocity measurement problem of high temperature burning particles, the measurement method which combines flame radiation and cross correlation method is presen-ted,and the measurement device has been designed to measure the velocity of burning pulverized coal particles in the flat flame burner experimental system.The two upstream and downstream measuring points at a distance of 6 mm are set to obtain the flame radiation signals of burning par-ticles.The velocity is determined from the cross-correlation analysis of the two signals.Thus, the time evolution of particle velocity under different conditions is obtained.Compared to the results of computational fluid dynamic,the relative deviations have been found to be less than 10%.The result shows that this method can provide a simple and effective method for measuring the burning particle velocity in the harsh environment such as coal combustion in a boiler and pro-pellant combustion in a solid rocket motor.

Development and application of pressure sensitive paint system in 2.4m transonic wind tunnel

Xiong Jian, Li Guoshuai, Zhou Qiang, Li Ping, Ma Husheng, Wang Hongbiao, Liu Xiang, Huang Hui

2016, 30(3): 76-84. doi: 10.11729/syltlx20150144

Abstract(180) PDF(20)

Abstract:
In recent decades,PSP (Pressure Sensitive Paint )measurement technique has been improved continuously and applied to engineering wind tunnel testing of two meter scale in many aerodynamic test institutions in the world gradually,for model surface pressure measure-ment,flow visualization on model surface and CFD result validation.A binary PSP measurement system with multi light sources and CCD cameras has been established in the 2.4m transonic wind tunnel,and the many problems affecting measurement accuracy and reliability in large intermittent transonic wind tunnel tests have been solved,such as temperature changing on mod-el surface,illumination uniformity and intensity changing,model vibration,as well as test data correction,spraying and coating calibration,and so on.Meanwhile it has been employed to the surface pressure distribution measurement tests of the large aircraft model and the NASA delta wing model.Test results indicate that PSP coating has little influence on model surface pressure distribution.The difference of the root mean square of Cp between PSP and conventional pressure taps is below 0.03 under the test conditions with Mach numbers ranging from 0.4 to 1.2 and angles of attack varying from -4°to 4°,which is equal to the measurements accuracy of continu-ous transonic wind tunnel of the same scale abroad.In a word,the new PSP system and tech-nique application can provide a new advanced measurement method for the configuration optimum design of flight vehicles and aerodynamics research.

Direct measurement of skin friction in hypersonic wind tunnel

Ma Hongqiang, Wen Haoju

2016, 30(3): 85-91. doi: 10.11729/syltlx20150118

Abstract(106) PDF(14)

Abstract:
The experiments of direct measurement of skin friction in hypersonic wind tunnels FD-03 and FD-07 of CAAA are introduced.Two-component and one-component strain-gage bal-ances are developed to the application of moving compression ramp experiment and wave rider ex-periment,respectively.In the experiments,the total pressure is 1MPa,total temperature is 360K and Mach number is 5.There are two balances installed in each model as measuring points. In the moving compression ramp experiment,the skin friction of plate is measured.The flow field is found to be interfered by the moving compression ramp,and the skin friction of the com-pressed ramp motion interference region is measured.In the wave rider experiment,the skin fric-tion of the model is measured and the relationship between the skin friction and the angle of at-tack has been found.Temperature correction is introduced to the experimental data processing. In all the experiments,the uncertainty is less than 1 2%.

High temperature strain measurement of the front edge structure in high thermal environment

Wu Dong, Chen Dej iang, Zhou Wei, Du Baihe

2016, 30(3): 92-97. doi: 10.11729/syltlx20150131

Abstract(178) PDF(8)

Abstract:
During the long time flight in the aerosphere,the hypersonic vehicles’front edge structures are heated badly and affected greatly by thermal stress.Therefore it is necessary to an-alyze the stress field of the front edge structure.The hot structure experiment of hypersonic ve-hicles’front edge was done in the arc heated wind-tunnel.During the experiment high tempera-ture strain was measured using the high temperature strain gages.In this paper,the experimen-tal equipment,the experimental condition,the experimental model and calibration of thermal output are introduced.The experimental data of two kinds of model materials including carbon composite and heat-resistant alloy are analyzed.The computational results verifies the experi-mental data.The temperature of the experimental strain measurement was 600℃.The experi-mental results show that the front edge model’s side flat is in a normal stress state.The results shall be an important reference for structure optimization design.

Study of micro flow visualization with nuclear magnetic resonance in core

Di Qingfeng, Hua Shuai, Gu Chunyuan, Ye Feng, Pang Dongshan, Jiang Fan, Yang Peiqiang

2016, 30(3): 98-103. doi: 10.11729/syltlx20150107

Abstract(259) PDF(8)

Abstract:
Core micro flow visualization is an important method to study the microcosmic mechanism of the chemical flooding.The latest results of core micro flow visualization by MRI technology in our research group was introduced in detail.Some questions on low field MRI core displacement system (MRICDS)were put forward,and improvement and optimization were made from the two aspects of hardware and software to eliminate interference factors.The exper-iments of fluid image test during water-flooding process were successfully carried out using the improved MRICDS.The real-time signals of NMR and MRI of the oil-water distribution during the flow test were collected,and NMR-T2 spectrums and oil or water distribution images were obtained in different stages.The images with high resolution can meet the request of visually an-alyzing the fluid distribution in the core.Experimental results show that residual oil decreases with PV increasing.The trendline of oil distribution drops rapidly first and then slowly.Images also show the phenomenon of residual oil gathering in the end area in core flow tests and its influ-ence range is about 4mm from the end.A new method of oil saturation by the oil-water distribu-tion map of MRI was introduced,and its results are consistent with that of the traditional method and the error is within 10%.This also shows that the reliability of the oil-water distribution map.This provides a new method for the study of oil saturation.Especially the other advantage
of the method is that it can analyze the oil-water saturation at any local position.The results also indicate that the new method of MRI is worthy of further development for fluid distribution visu-alization during core micro flow.

2016 Vol. 30, No. 3