实验流体力学

The analysis of hypersonic impulse facility building course in Calspan

Lyu Zhiguo, Li Guojun, Zhao Rongjuan, Luo Yicheng, Kong Rongzong, Zhong Yong, Jiang Hua

2014, (5): 1-6. doi: 10.11729/syltlx20130082

Abstract(248) PDF(12)

Abstract:
This paper describes and analyses the serial hypersonic impulse facility building course of Calspan Corporation in USA.To meet the needs of different research,Calspan corpora-tion has built six shock tunnels and two expansion tunnels successively which include 1 1 ×1 5 inch shock tunnel,48 inch shock tunnel,96 inch shock tunnel,high enthalpy shock tunnel,LENS I shock tunnel,LENS II shock tunnel,LENS X expansion tunnel and LENS XX expansion tunnel. The dimension,simulation capability and testing technique all represent the tiptop level in the corresponding period.The analysis of LENS series impulse facility building course of Calspan Corporation would provide helpful information for building our national impulse facility and de-veloping test measurement tecnology.

Study on velocity oscillating phenomenon of free falling bodies

Li Yiming

2014, (5): 7-12. doi: 10.11729/syltlx20130100

Abstract(173) PDF(8)

Abstract:
In order to study the falling velocity oscillating phenomenon,the characteristic of suspending obj ects of five typical rigid bodies inside up-flow were experimentally studied by using a wind tunnel with vertical test section based on the principle of relative motion.The rigid objects include ball,cube,cuboid,cylinder and disc.The mean wind velocities inside the wind tunnel test section were measured by Pitot-Tube and the dynamic status of the obj ects before and after its suspension were recorded by CCD camera and quantitatively analyzed.The experimental re-sults show that the obj ects of symmetrical bodies can maintain a comparatively stable suspension state,while those of asymmetrical bodies continuously oscillate with changing attitude angle due to different drag coefficient and pitch coefficient on the asymmetrical objects.In other words,the symmetrical objects can reach a stable maximum falling speed during free fall,while the asym-metrical bodies are hard to reach expected maximum falling speed.Besides experimental study,a 2-D Computational Fluid Dynamics (CFD)model combined with dynamic mesh technology was also performed,from which the drag coefficient,pitch coefficient and the trajectory of the square inside the flow were obtained.The simulation results can be used to quantitatively explain the falling velocity oscillation of the asymmetrical free falling bodies.

Experimental study on the evolution of heavy gas cylinder under reshock condition by PIV method

Zhang Fu, Zhai Zhigang, Si Ting, Luo Xisheng

2014, (5): 13-17. doi: 10.11729/syltlx20130074

Abstract(143) PDF(10)

Abstract:
Evolution of a membrane-less heavy (SF6 )gas cylinder under reshock condition is experimentally investigated in a horizontal shock tube with particle image velocimetry (PIV ) method.As a fundamental interface configuration,gas cylinder evolution impinged by a single shock wave is extensively investigated while the related research under reshock condition is sel-dom performed.Illuminated by a continuous laser sheet,the interface morphology after the inci-dent shock and reshock impact is characterized by glycol droplets and captured by a high-speed camera.The generation and development of counter-rotating vortex pair after incident shock im-pact is observed and secondary vortex rings,which have opposite rotating directions with the o-riginal vortex rings,are generated after the reshock passage because of the opposite pressure gra-dient induced by reshock compared with the incident shock.Because the velocity of the flow field after reshock is very small,the PIV measurement based on the Matpiv procedure is employed to capture the flow field after reshock.The continuous velocity and vorticity fields are obtained with the help of the continuous light source and high speed camera.Compared with the PIV algorithm based on the double-exposure technique,continuous velocity field can be obtained in a single test run based on the high-speed technique in this experiment.The circulation derived from PIV measurements is compared with the existed analytical model and a good agreement is achieved, which validates the feasibility of the experimental method.

Experimental study on flow drag reduction characteristics of xanthan gum solution in smooth pipes with different diameters

Yu Yanfei, Li Mingyi, Zhao Wenbin, Hou Jinliang, Li Changfeng

2014, (5): 18-23. doi: 10.11729/syltlx20130101

Abstract(97) PDF(4)

Abstract:
Experimental study on drag reduction characteristics of xanthan gum solution in smooth pipes with different diameters has been conducted.The variable parameters are as fol-lows:(1)the pipe diameters,5,10 and 20mm,respectively;(2)the concentration of xanthan gum solution ranging from 50 to 550ppm;(3 )fluid velocity,characterized by flow generalized Reynolds number in the range of 0~50000.The pipe pressure dropΔp and flow volume flux Q under different conditions have been measured.The relationship between drag reduction and con-centration of xanthan gum solution is obtained,and the influence of Reynolds number on friction factorλis also investigated.It is observed that the drag reduction effect of xanthan gum solution relys obviously on the concentration of the solution,percent drag reduction increasing with the increase of xanthan gum solution concentration until it reaches the optimum saturation concentra-tion where the percent drag reduction is mainly keeping constant.The experimental results also show the drag reduction type difference under low and high Reynolds number flow conditions for xanthan gum solution in three pipes with different diameters.

Experimental study on unsteady loads of a synthetic jet at airfoil trailing edge---B:analysis of unsteady aerodynamic loads

Zhang Weiwei, Zhai Jian, Liu Xiaobo, Ye Zhengyin

2014, (5): 24-32. doi: 10.11729/syltlx20120189

Abstract(174) PDF(6)

Abstract:
A low frequency high power synthetic j et actuator is designed to study the effects of the synthetic jet near the trailing edge of NACA0015 airfoil.The effect of the spout speed,fre-quency and other parameters on the aerodynamic loads can be studied by changing the ground cyl-inder stroke or the operating frequency of the motor.The experimental results show that the in-teraction of the synthetic jet with the upstream can modify the aerodynamic loads obviously.If one jet works,the loads amplitude in the “blowing”process is about 3 times of that in the “suck-ing”process.Moreover,when two jets work,the amplitudes of lift and moment coefficients are not simply the sum of relevant amplitudes of the one jet case,but lie between the amplitudes of one jet work and two jets work sum.The amplitudes of the lift and momentum coefficients show a good proportional relation to the amplitude of the jet velocity,and the amplitudes of the loads decrease with the increase of the reduced frequency.When the stroke of the synthetic jet is fixed, changing the rotate speed of the servomotor,there is a linear relation between the amplitude of the loads coefficients and the rotate speed.

Study on j et characteristics of slim-hole hydraulic pulsed cavitating-j et generator by in-house experiment

Lan Qichao, Li Gensheng, Shi Huaizhong, Wei Minghui, Shi Shuaishuai

2014, (5): 33-38. doi: 10.11729/syltlx20130094

Abstract(146) PDF(3)

Abstract:
The technology of hydraulic pulsed cavitating-j et has demonstrated in conventional wellhole field application that it can improve ROP(Rate of Penetration)significantly.Therefore, for economically developing offshore oil and gas resources in marginal regions,combining slim-hole single-channel well and the ROP improving technology of hydraulic pulsed cavitating-jet,a small-size(outside diameter:120mm)hydraulic pulsed cavitating-jet generator has been devel-oped.In order to figure out its jet characteristics,we have made a research by laboratory experi-ment on its parameters of pulsed frequency,the inlet/outlet pulsating pressure amplitude,pres-sure loss and jet characteristic of self-oscillating nozzle.The test results show that the pulsed fre-quency increases linearly with the increase of the flow rate,the inlet/outlet pulsed pressure am-plitude increases with the increase of the flow rate,the pressure loss increases quadratic curve with the increase of the flow rate.When the flow rate is 10L/s,the pulsed frequency is 8Hz,the out-let pulsed pressure amplitude is 1.2MPa and the pressure loss is 1.6MPa.The self-oscillating nozzle can bring about negative pressure and cavitation.A research on the mechanism analysis of ROP im-proving of hydraulic pulsed cavitating-jet has also been made.Its mechanism contains 2 parts:hydraulic j et can improve the efficiency of cuttings cleaning and cavitating-j et can improve the ef-ficiency of rock breaking.

Identification of aerodynamic admittances by considering the effect of incomplete span-wise correlation of buffeting forces on sectional model

Xu Ziran, Zhou Qi, Zhu Ledong

2014, (5): 39-46. doi: 10.11729/syltlx20130113

Abstract(89) PDF(6)

Abstract:
The relationship between the spectra of the distributed buffeting forces on a model cross section and the total buffeting forces on the whole sectional model measured by a base-sup-ported force balance in wind tunnel test of sectional model was derived first in this paper by consider-ing the span-wise incomplete correlation of distributed buffeting forces on the sectional model.By taking a quasi-flat plate cross section as an example,sectional model wind tunnel tests of force measurement and simultaneous pressure measurement were carried out in a grid-generated turbu-lent wind field to obtain the spectra of the total buffeting forces and the span-wise correlation functions of the distributed buffeting forces.On this basis,the equivalent aerodynamic admit-tance functions of the quasi-flat plate were calculated in the light of the equivalent admittance method whilst the six-component aerodynamic admittance functions of the quasi-flat plate were identified by using a least square approach based on a colligated residue of the auto spectrum of buffeting force and the cross-spectra between buffeting force and fluctuating wind velocities,ab-breviated as “colligated least square approach of auto and cross spectra”.The effect of the span-wise incomplete correlation on the identification results of the aerodynamic admittance were then discussed and the identified results were compared with Sears function,the theoretical solution of the aerodynamic admittance function of flat plate under the vertical fluctuating velocity of w.The results show that the ignorance of the span-wise incomplete correlation of the distributed buffe-ting forces on the sectional model,namely the direct employment of the averaged buffeting force as the distributed one based on the assumption of complete correlation of distributed buffeting forces along the model span,will lead to underestimated values of the identified aerodynamic ad-mittance functions,and the extent of the underestimation will rise with the increase of frequency. Furthermore,the effect of the span-wise incomplete correlation of buffeting force on the buffe-ting drag related components of aerodynamic admittance is more remarkable than that on the buf-feting lift force or torsional moment related components of aerodynamic admittance because the span-wise correlation of buffeting drag is much weak than those of the buffeting lift force and tor-sional moment.It can also be found that the back-calculated spectra of distributed buffeting forces acting on the model obtained by using the six-component aerodynamic admittance functions identified with the colligated least square approach of auto and cross spectra are quite close to those measured in the test.The two components of aerodynamic admittance related to the verti-cal fluctuating wind velocity (w)as well as the buffeting lift force and torsional moment are also rather close to the Sears function.These two facts verify the reliability of the colligated least square approach of auto and cross spectra for the identification of aerodynamic admittance.

Time-frequency analysis on differential pressure signal of two-phase flow based on EEMD

Sun Bin, Liu Tong, Zhao Peng

2014, (5): 47-52. doi: 10.11729/syltlx20130036

Abstract(164) PDF(4)

Abstract:
In order to study the dynamic characteristics of gas-liquid two-phase flow,a time-frequency analysis method of gas-liquid two-phase flow is proposed based on ensemble empirical mode decomposition (EEMD),using V cone flowmeter as a measuring device and the high fre-quency differential pressure transmitter to obtain the dynamic signal under different flow pat-terns.In order to lay the theoretical foundation for the further research on gas-liquid two-phase flow mechanism and accurate measurement of the flow,the differential pressure signals of the gas-liquid two-phase flow for different flow regimes are analyzed thoroughly.The analysis shows that EEMD exhibits a satisfying mixing decomposition ability,as it can extract frequency compo-nents of differential pressure signal of two-phase flow and the real-time situation accurately.It provides the theoretical basis for the identification of two-phase flow in future and has a high val-ue to engineering application.

Study on wind pressure characteristics on quasi-oval shaped iced conductor at critical Reynolds numbers regime

Ma Wenyong, Zhang Xiaobin, Li Lingzhi, Liu Qingkuan

2014, (5): 53-58. doi: 10.11729/syltlx20130090

Abstract(152) PDF(4)

Abstract:
By employing the rigid model wind pressure test,the wind loads distribution on quasi-oval shape iced conductor is obtained at different Reynolds numbers,and the effects of Reynolds number on wind loads as well as galloping stability in the direction transverse to the mean wind direction are analyzed by comparing the mean wind loads,fluctuating wind loads and wind force spectra.When the Reynolds number reaches the critical range,compared to the situa-tion at sub-critical range,the mean drag coefficients decrease,and mean lift coefficients occur at the symmetric case and severely vary with the wind direction;wind pressure coefficients are sen-sitive to the wind directions.Vortices shedding,which is supposed to be regular at sub-critical range,is irregular at critical range;the correlation of wind pressure around the cross section is weakened,and predominate frequency disappears.The steep slope of the lift coefficient versus angle of attack corresponding to Reynolds number at critical range makes the galloping in the di-rection transverse to the mean wind direction easy to happen.

Vortex-induced vibration measurement and analysis of model-sting system in wind tunnel

Zhu Bo, Wang Yuanxing, Yu Yongsheng

2014, (5): 59-64. doi: 10.11729/syltlx20130091

Abstract(146) PDF(6)

Abstract:
Long cantilever stings that support aerodynamic models in wind tunnels are a po-tential source of vibration problems which would impair the test data quality.It is reported in many documents to use the method of setting sensors on models to measure vibrations of the model-sting system,but setting sensors on small models is hard to realize.In this paper,a 0.55m×0.4m low turbulence aeroacoustic wind tunnel model-sting system is employed as the experimental object, acceleration sensors which directly measure the equipmentvibration and hot wires which indirectly measure the model wake are made use of jointly.The vortex-induced vibration models of the sys-tem are measured and analyzed.Wake measurement by hot wire to acquire vibration parameters of the model is tried,and this method is easy to be emploied for small models.At the same time, the methods of accelerator signal frequency domain filtering and frequency domain integration is used to acquire vibration model parameters of the model-sting for purpose of comparison with da-ta of hot wire.This method could improve the SNR of effective signal.With the method of accel-eration sensors power spectrum analysis,three order vibration frequencies of 31.1,120.9 and 221.4Hz of the system are acquired.With the method of frequency domain filtering and frequen-cy domain integration,the vibration mode and node of the system are acquired.With the method of hot wire measuring wake,vortex shedding frequencies of 31.1 and 124.1Hz,and the model buffet boundary are acquired.Experimental results show that,the results show that,the method of hot wire measuring model wake vortex shedding frequency for the analysis of aircraft model vi-bration is propitious to be applied for small models,since it has less interference with model sur-face flow field than the method of setting sensors on model surfaces.Therefore,the hot wire method is a practical method for vortex-induced vibration measurement.

The component characteristics test study of a missile model with complexity configuration in high speed wind tunnel

Li Fangji, Gao Chao, Li Weiqun, Cao Xiaolong, Li Qiang, Zhang Yue, Wang Junlan

2014, (5): 65-70. doi: 10.11729/syltlx20130068

Abstract(130) PDF(7)

Abstract:
The component characteristics test of the missile model was conducted in the FL-28 wind tunnel.The missile’s configuration is complicated.The angels of attack ranged from-6°to 10°,and angels of sideslip were from-6°to 6°.Protective cover,left wing and rectifier covers were involved in the test.A 5-component balance was used to obtain force and moment data of protective cover,and the component characteristics was acquired when the test data were correc-ted by the result of pressure measurement of the aperture.Three 3-component balances were used directly to obtain component characteristics data of left wing and rectifier covers.The test result can be applied for structure design of those components.The correction method for the da-ta of protective cover is verified,and it could provide some experience for the later tests.

Development of the 70kN strain gauge balance calibration system

Xie Bin, Shi Yujie, Yi Guoqing, Wang Chao

2014, (5): 71-75. doi: 10.11729/syltlx20130078

Abstract(24) PDF(6)

Abstract:
To meet the static calibration requirement of the balances used in force tests of 2 meter scale high speed wind tunnel,a 70kN strain gauge balance calibration system is developed. Based on the traditional OFAT method,the scheme for four degree of freedom,balance body ax-is system replacement and automatic calibration is adopted.Standard weights are applied to pro-vide accurate calibration loads by using automatic loading weights device,which controls weights independently.Through the double cross hinge force acting point positioning device and the but-terfly shape load-adapter,balance can be loaded exactly.Gapless replacement transmission mech-anism ensures precise replacement of the balance.The final calibration system can meet the cali-bration requirements of different types of balances such as sting and ring ranging from 20kN to 70kN loading.

Design and implementation of high accurate digital valve for FL-3 wind tunnel

Ji Jun, Deng Xiangdong, Bai Yuping, Song Xiaoyu, Li Yong

2014, (5): 76-80. doi: 10.11729/syltlx20130084

Abstract(138) PDF(11)

Abstract:
The technical target ,the scheme,the type of valve and the design of nozzle for the design of the digital valve system used to controll mass flow and pressure are introduced in this paper for power simulation testing in FL-3 wind tunnel.The experimental results show that the measuring accuracy of mass flow and pressure control is ±5g/s respectively for the digital valve system,and the digital valve also has the advantages of quick and stable control.The digital valve system can satisfy the demand of accurate control of the flow rate and pressure for aircraft power simulation testing in the FL-3 wind tunnel.

Surge margin test and research of AV90-3 axial compressor in 0 .6m continuous transonic wind tunnel

Zhou Enmin, Cheng Song, Xu Jing, Liu Kai, Zhang Wen, Xiong Bo, Wang Yitian

2014, (5): 81-85. doi: 10.11729/syltlx20130083

Abstract(155) PDF(15)

Abstract:
In order to determine the AV90-3 axial compressor’s safe working area in the 0.6m continuous wind tunnel,the test method of reducing the compressor’s inlet volume flow to deter-mine the surge point and that of monitoring the pressure to distinguish the surge are employed. The surge margin of the AV90-3 axial compressor is accurately determined.It comes to the con-clusion that the surge margin is extended to the top-right as the static blade angle increases and the surge margins both above and below atmospheric pressure fit well with that at atmospheric pressure.The surge is prevented occurring effectively by selecting the ratio of the inlet volume flow to the pressure as the anti-surge control parameter,setting alarm and anti-surge curve,and taking by-pass circumfluence.It can provide reference to large-scale continuous wind tunnel com-pressor’s surge margin test and anti-surge control.

The measurement of shock wave velocity by heat flux probe

Zhang Shizhong, Li Xian, Li Jinping, Chen Hong, Yu Hongru

2014, (5): 86-91. doi: 10.11729/syltlx20130098

Abstract(174) PDF(10)

Abstract:
Shock wave velocity is one of the most important parameters in shock tube for de-termining the running states.It can be measured through shock pressure or optical method,of which the cost will be high in large systems.Ionization-probe is an effective means of determining the velocity of detonation or strong shock waves by using the conductivity behind the shock wave, but it may not meet the experimental requirements under the condition that the shock wave veloc-ity is so low that the air behind the shock wave cannot reach the ionization temperature.A ther-mocouple flux probe with high frequency response is used in our measurement system to over-come the aforementioned disadvantages.Based on traditional ionization-probe circuit,the ther-mocouple probe measurement circuit is redesigned.The shock wave signal is amplified and locked to trigger the pulse generating circuit to obtain the shock velocity signal.The key of the circuit design is that the secondary amp signal interference is particularly large after the thermal simula-tion network,due to the load through a capacitor,therefore,the magnification of the secondary amplification circuit cannot be too high,but the amplitude of heat flux signal is determined by the magnification,so the relationship between the two factors need to be balanced.Temperature and heat flux signals are used as trigger signals respectively.The delay times contrasted with piezoe-lectric sensors are inconsistent when the trigger signal is temperature.The first pulse delays 130 microseconds,and the second delays 80 microseconds,which is because the limit trigger voltages have error.When the trigger source is heat flux signal,the circuit can be triggered without delay to obtain more accurate shock wave velocity.The resutls show that only heat flux signal can meet the time requirements of shock velocity.This method overcomes the drawbacks of traditional i-onization probe,and can be widely applied to various shock tubes for shock wave velocity meas-urement.

Effects of adiabatic structure on heat flux measurement using a slug calorimeter

Yang Qingtao, Bai Hanchen, Zhang Tao, Wang Hui

2014, (5): 92-98. doi: 10.11729/syltlx20130085

Abstract(101) PDF(5)

Abstract:
Slug calorimeter is widely used in thermal protection tests,and lateral heat conduc-tion is one of the most important sources of heat flux measurement error using a slug calorime-ter.An improved adiabatic structure is designed based on slug calorimeter heat transfer analysis, and a heat loss correction method is proposed based on semi-infinite body assumption.FEA(Fi-nite Element Analysis)model is developed to study effects of thermal contact resistance (TCR) between the slug and the adiabatic structure on data reduction results.If TCR is large (R= 1 × 10-3 m2 ·K/W),the max measurement error is less than-9% without correction and more than 20% with correction.On the other hand,when TCR is small (R= 1 ×10-4 m2 ·K/W),the error is about-20% without correction and less than 1 .5% with correction.It is concluded that the correction method can only used in the situation when TCR can be neglected.Numerical simula-tion results also show that using the improved structure with a metal sharp wedge structure add-ed near the surface of adiabatic layer,the max temperature of adiabatic material decreases from o-ver 2000℃ to less than 300℃,which means that with the improved structure,the adiabatic ma-terial is protected efficientlly from ablation.The heat transfer area between the metal wedge and the slug is only about 2 .9% of the total lateral area,which hardly effects selection of data reduc-tion methods.

Study of the T type back-supported tube and its application in EMU flow test

Xu Liangzhong, Pan Yunyan, Tang Hong

2014, (5): 99-103. doi: 10.11729/syltlx20140010

Abstract(102) PDF(4)

Abstract:
In order to solve the problem that the traditional velocity measurement instruments can not be applied to Electric Multiple Units (EMU),because of the reverse of the flow and the limited space,a new type tube called T back-supported tube was developed.It has better total port.By the wind tube test,the correlation between velocity coefficient and the different varia-bles such as bend segment length,wind yaw angle,flow velocity and so on was discovered.A verification flow test of the flesh air tube in the full-scale experiment can prove its excellent char-acters.The best ratio between length and diameter of the bend segment is 2,and under this size, the velocity coefficient under the dynamic pressure 138Pa was only changed 1.34% as the pres-sure varied.The average velocity coefficient in the range of 353Pa of the dynamic pressure was 0.741.The wind yaw angle variation does have effect to the velocity coefficient of the T type back-supported tube.It is indicated that 10 degrees increasing can make the velocity coefficient decrease 6 .1 2%.The T type back-supported tubes were well applied in the EMU fresh-air tube flow testing;the errors between the testing results and the rated values were all within 4.02%. It is pointed that while the structure of the T back-supported tube is simple and symmetric,it is also less sensitive to the velocity and wind yaw angle variation.The tube worked stable and relia-ble and the result was also precise.

Comparison of the performance of cobra probe and hotwire in circular cylinder wake

Wang Hanfeng, Li Zhuofeng, Lin Xiangde

2014, (5): 104-110. doi: 10.11729/syltlx20130093

Abstract(299) PDF(33)

Abstract:
The performance of cobra probe and hotwire is compared in a circular cylinder wake at the Reynolds number of 7200,including time-averaged velocity,Reynolds stresses,probability density functions,auto-correlation coefficients and spectra.Based on the experimental results,it is found that the rejection rate of cobra probe increases with turbulence intensity.However,its effect on the time-averaged results is negligibly small.Although the acceptability rate of cobra probe is higher than 95%,it over estimates the Reynolds stresses compared to hotwire.Particu-larly,for the main Reynolds shear stress u*v*,the difference of measurements between cobra probe and hotwire is significantly larger than those for the Reynolds normal stresses.Since cobra probe can not capture high frequency fluctuation,the auto-correlation coefficients of velocities present stronger periodicity relative to that of hotwire.The responses of cobra probe are different for u and v,resulting in significant difference in their spectra in the inertial sub-range,and thus it can not reveal the local isotropy of small scale turbulence in the inertial sub-range.

2014, (5): 111-112.

Abstract(41) PDF(6)

Abstract:

2014 Vol. 28, No. 5