实验流体力学

The experimental investigation on the effect of rearward Mini-TED to the aerodynamic characteristics of an airfoil

Xia Jun, Daichin

2015, (5): 1-7,25. doi: 10.11729/syltlx20140148

Abstract(120) PDF(6)

Abstract:
The pressure distribution,aerodynamics and PIV velocity fields of a NACA23012 airfoil mounted with a rearward Mini-TED captured in a low speed wind tunnel tests are intro-duced and compared with experimental results of a NACA23012 prototype airfoil in this paper,in order to investigate the influence of the Mini-TED to the flow field and aerodynamics loads of the airfoil.The Reynolds number is 1.3×10 5 based upon the chord length of the airfoil.The pressure distribution on the airfoil is measured using the pressure tubes and pressure transducers,and then the results are integrated to obtain the lift force and pressure drag acting on the airfoil.The total drag is measured using the comb of stagnation pressure based on the momentum theorem. The velocity fields around the airfoil are captured by a PIV system.The rearward Mini-TED in-duces changes to the flow velocity around the airfoil and the wake flow structure,which leads to the variation of the pressure distribution on the suction and pressure surfaces and the increase of both the lift and pressure drag.The position of the front stagnation point of the airfoil with a Mini-TED shifts downstream slightly compared with that of the NACA23012 prototype airfoil, which consequently leads to the increase of the flow velocity on the suction surface and the sup-pression of the flow separation near the trailing edge.

Research on aerodynamic parameter identification technology in wind tunnel free-flight test based on Maximum Likelihood Estimation

Zhang Tianjiao, Qian Weiqi, He Kaifeng, Wang Qing

2015, (5): 8-14. doi: 10.11729/syltlx20140116

Abstract(122) PDF(9)

Abstract:
Using the Maximum Likelihood Estimation method can avoid severe errors of aero-dynamic coefficients as a result of direct differentiating the measured data in wind tunnel free-flight test.This paper introduces the rationale and methodology of the aerodynamic parameter i-dentification technology in the wind tunnel free-flight test in detail.Simulation and test examples are presented.The identification results indicate that the aerodynamic parameter identification from wind tunnel free-flight test data is an effective method in study of aerodynamic characteris-tics of aircrafts.Although force derivatives are hard to identify,moment derivatives are easy to i-dentify and the identification results are close to the engineering results.Meanwhile,the increase of the number of sample points,the improvement of precision of measurements,the installation of overload measuring equipment and the improvement of machining level of test models are all favorable for enhancing the reliabilities of results.

Study on error mechanism and uncertainty assessment of heat flux measurement in shock tunnel

Zeng Lei, Gui Yewei, Wang Anling, Qin Feng, Zhang Haoyuan

2015, (5): 15-25. doi: 10.11729/syltlx20140135

Abstract(143) PDF(12)

Abstract:
The influence of thermal sensors’mathematical and physical model and data pro-cessing method on the acquisition of heat flux data were analyzed,and the difference between the processed and actual heat flux data was quantitatively presented upon that.The changes of the flow field and wall heat flux caused by the curvature variation of the stagnation region due to the installation of sensors were also discussed in this paper.The correction method and correspond-ing coefficients were proposed for different types of sensors and different compositions of sensi-tive elements.The correlation between temperature rise and heat flux variation on the sensor sur-face was studied and the modified formula was given to modify the original data.Moreover,the uncertainty estimation method of aerodynamic heating measurement was established according to different error sources,and the influences of small changes of inflow condition on the heat flux and sensors’random factors on heat flux measurement were also analyzed.Based on the random error analysis theory,the uncertainty assessment method was established,based on which the uncertainty of heat flux measurement in the validation experiment was obtained.In conclusion, some valuable results and suggestions about the sensor design and aerothermal experiments were obtained,and these results can improve the accuracy of heat flux measurement further and thus have prominent application prospect in near-space hypersonic vehicle development.

Experimental study of turbulent mixing of the cloud with unsaturated air under different humidity

Liu Xiaoxia, Lu Zhiming, Huang Yongxiang, Zhou Quan, Liu Yulu

2015, (5): 26-31,44. doi: 10.11729/syltlx20150017

Abstract(136) PDF(3)

Abstract:
This paper presents PIV results of turbulent mixing of the cloud and unsaturated air with different environmental humidity in a small cloud chamber (80 ×80 ×100cm3 ).Turbu-lence characteristics such as the variation,skewness and flatness factors of two-dimensional ve-locities are first calculated to demonstrate the anisotropy of such turbulent fields of several centi-meters scale.Experimental results further show that the departure of the probability density function(PDF)of the vertical velocity component from the standard Gaussian distribution be-comes more obvious at the tails with the increase of unsaturated environmental humidity.The anisotropy of the turbulence is further revealed by the difference between the second-order struc-ture functions of two velocity components.The isotropic ratio (the ratio of transverse structure functions to longitudinal structure functions)is far different from the theoretical value for homo-geneous and isotropic turbulence and its dependence on the environmental humidity is complicated and needs further investigation.

Optimization design of inner-structure of the slot-jet in aircraft cabin based on investigation of multi-scale characteristics of slot turbulent jet flow

Ge Wentao, Guo Yong, Dai Shen, Jiang Nan, Liu Junjie

2015, (5): 32-37. doi: 10.11729/syltlx20140151

Abstract(140) PDF(2)

Abstract:
In order to solve the distribution heterogeneity problem of the mean span-wise ve-locity field of the slot outlet in MD-82 airliner cabin,we designed the slit-shaped inner core struc-ture in order to make the final mixture of the slot flow more uniform,the development of the tur-bulence is more sufficient and the distribution of the mean stream-wise velocity field is more hom-ogeneous.Hot-wire anemometry is used in the simplified cabin model experiments,based on which the research is carried out on the optimization design of inner structures of the slot-jet in aircraft cabin and the multiscale characteristic analysis of the turbulence.The slot-jet flow fields in model cabin environment with different inner-structure are finely measured by constant-tem-perature anemometry system.The resolution of the constant-temperature anemometry system is higher than the smallest time-scale of turbulence (inner structure and dissipation time-scale). The actual velocity field is analyzed in the stream-wise direction and normal direction respective-ly.Furthermore,based on the comfort theory,the wavelet-transformations are applied for the characteristic analysis of the multi-scales eddy and the analysis of the distribution of energy.The variation of the mean velocity beyond the slot outlets reveals the decaying regularity of the veloci-ty in the stream-wise direction and the flow irregularity in the normal direction.Results from the wavelet transformation analysis indicate that the change of energy proportion of different scale ed-dies is connected with the evolution of the slot-jet flow field.It can be seen from the results that small scale vortices generate entrainment and merge into large scale vortices on account of the in-crease of the viscosity and the decrease of the inertness in the far field of the turbulence jet flow field,which is called inverse energy cascade.It has a significant impact on the thermal transmission and the diffusion of contaminant.It’s the main reason of the draft sensation discomfort.By the contrast experiments,the slit-shaped core inner structure is designed so that the final mixture of the slot flow is more uniform and the development of the turbulence is more sufficient.From the perspective of comfort analysis on the flow fluctuation frequency,the flow characteristic frequen-cy of the flow field beyond the outlet with the designed core structure has remained to be about 21.83Hz,while the air fluctuation frequency which results in highest discomfort is 0.2~0.6Hz. Therefore the design is worked.

Design and experimental analysis of three-stage compression cone-derived waverider

Lyu Zhenjun, Wang Xudong, Ji Weidong, Wang Jiangfeng

2015, (5): 38-44. doi: 10.11729/syltlx20150003

Abstract(157) PDF(6)

Abstract:
In order to give full play to the waverider forebody’s pre-compression effect,a new design method for the multistage compression waverider is presented based on the osculating cone theory.A three-stage cone-derived waverider is designed by using this design method.Numerical simulation results show that three conical shock waves intersect at the bottom section as expected in design.The three-stage compression cone-derived waverider used in wind tunnel tests has an expanded upper surface.At the bottom section the waverider is connected with the inlet.The shape of the inlet lip is designed to match the contour of the three conical shock waves intersec-tion.Experimental research on the waverider forebody-inlet model is conducted.It is found that the shock wave shape is in good agreement with the numerical simulation result.Therefore,the correctness of the design method is validated.

Research on optimal design method for wind tunnel strain gauge balance based on iSIGHT

Xiang Guangwei, Wang Jie, Shi Yujie, Yi Guoqing

2015, (5): 45-49,59. doi: 10.11729/syltlx20150013

Abstract(134) PDF(5)

Abstract:
The main point of strain gauge balance design is to optimize the configuration of the balance.With the design requirements fulfilled,it is optimal to increase the stiffness,reduce the stress concentration and diminish the interactions among the components in order to improve the quality of the balance.The current trend of balance optimal design is to utilize methods such as perpendicular calculation design method,sequence quadratic optimization method,genetic algo-rithm optimization method,etc,and conduct simulation via MathCAD,Matlab,VC++,AN-SYS,etc.Balance optimal design is a multi-objective optimization design problem.Abundant empirical experiences are required in utilizing both the analytical method and the finite element method (FEM),but still the global optimal solution is hard to obtain.Considering the relations between the dimensions and geometries of various balance configurations,layered and parallel op-timal strategies are proposed.An optimal design method for the wind tunnel strain gauge rear-sting balance with six components based on iSIGHT is introduced.The significant effects of bal-ance design variables to the optimal objective are studied by design of experiment (DOE)so that a set of important variables are selected to set up an approximate 3D parameterized model.The parametric modeling method and the finite element method are applied.An optimization flow is automatically running in iSIGHT by integrating many design tools such as UG,ANSYS,EX-CEL,etc.General optimal algorithms are provided by iSIGHT and a lot of commercial software can be integrated to support the automatic running.This method offers an economical and easy way to improve the balance design quality.

Strain gauge balance development for force test on small aspect ratio flying wing high speed standard model

Shi Yujie, Huang Yong, Tian Zhengbo

2015, (5): 50-54. doi: 10.11729/syltlx20150015

Abstract(135) PDF(4)

Abstract:
There is a large difference between the longitudinal and lateral aerodynamic charac-teristics of a small aspect ratio flying wing aircraft,which presents a major challenge to the meas-urement and calibration of a strain gauge balance.According to the aerodynamic characteristics and to meet the aerodynamic test requirements of the aircraft,a specialized balance is designed by improving the combination element which is made up of sheet-beams and bar-beams.The sensi-tivities of the five components of the babance except for the axial force component are high e-nough for measurement,with the lateral components especially improved in the balance design. The lengthening thwart Π beam is adopted as the axial force element of the balance which can re-duce the interference to the axial force measurement.Longitudinal shock vibration is enforced on the load-adapter to take down it from the balance,and this is also the way to take down the test model.The balance has already passed relevant force tests in the wind tunnel.

Research on the wind tunnel test techniques for micro-pitching-aerodynamics of re-entry body

Zhao Junbo, Fu Zengliang, Liang Bin, Zhang Shiyu, Gao Qing

2015, (5): 55-59. doi: 10.11729/syltlx20150027

Abstract(130) PDF(6)

Abstract:
To accurately measure the micro-asymmetric pitching-aerodynamics of re-entry body remains a challenge for wind tunnel tests.An articulated free-oscillation system based on ball bearings is introduced to measure the dynamic stability derivatives and the static moment simultaneously.The ball bearings provide the degree of freedom in the pitching channel and pro-tect the test model from rupture when elastic beams are fractured because of fatigue.The oscilla-tion frequency and signal quality of the model can be regulated by optimizing the structural di-mension of the detachable elastic beam.The pitching free-oscillation test conducted in Φ500 hy-personic wind tunnel,where the pitching moment reaches the order of 10-6 ,demonstrates the ac-curacy and reliability of this system.

Measurements of cylinder’s wake by Tomo-PIV

Xu Xianghui, Jiang Jiali, Niu Zhongguo, Ning Jipeng, Liu Jie

2015, (5): 60-64. doi: 10.11729/syltlx20150022

Abstract(187) PDF(19)

Abstract:
Tomographic particle image velocimetry (Tomo-PIV)is an advanced optical meas-urement technology,which can acquire three-dimensional three-components (3D3C)flow field structure quantitatively in a complete volume,and can be used as an effective method on turbu-lence,vortex interference and other complex three-dimensional flow field measurement.In order to achieve the measurement application of Tomo-PIV in the FL-5 wind tunnel with 1.5m diame-ter test section of AVIC Aerodynamics Research Institute,the wake of a cylinder with 12mm di-ameter is investigated by means of Tomo-PIV.The flow speed is 15m/s,the measurement vol-ume is illuminated by a 2 ×200 mJ laser,and four 2048 ×2048 pixels CCD cameras with 85mm lens are used to record particles images from different directions.By solving a series of engineer-ing problems,such as diffusion of particles and optical path design,we successfully obtained the Karman rollers flow structure of the cylinder’s wake.Then,we studied the method of the data processing.The measurement volume extends approximately over a region of 95mm×70mm× 8.5mm with the shortest side in the direction of the depth of field,and the particle image spatial resolution is about 20 pixels/mm.There are tens of thousands of vectors recorded at every snap-shot.We can obtain a lot of information about the flow field by Tomo-PIV,much more than that obtained by 2D PIV or stereo-PIV measurement.

Uncertainty analysis in submarine standard model resistance test

Shi Shengzhe, Zheng Yaxiong

2015, (5): 65-71. doi: 10.11729/syltlx20150002

Abstract(147) PDF(9)

Abstract:
To improve the test accuracy in the towing tank,repeated resistance tests of the submarine standard model were conducted.According to ITTC recommended procedures and guidelines for uncertainty analysis in experimental liquid dynamics,the test results were ana-lyzed.Uncertainty is caused by the bias limits related to the submarine standard model geomet-rical form,velocity,resistance,temperature,density and kinematical viscosity,and accordingly the bias limits were calculated.The standard deviation was got by six repeated resistance tests, and then the precision limits were calculated.The total uncertainty was estimated.The results show that,the bias limits of the kinematical viscosity coefficient caused by temperature uncer-tainty contributes to 97% of the bias limits of the friction resistance coefficient;98% of the bias limits of the total resistance coefficient comes from the bias limits of the wet surface area;as the test velocity increases,the total uncertainty of the total resistance coefficient and friction resist-ance coefficient reduces.

Research on flutter test technology of continuously adjusting dynamical pressure in high-speed wind tunnel

Guo Hongtao, Yan Yu, Yu Li, Lyu Binbin, Du Ning

2015, (5): 72-77. doi: 10.11729/syltlx20150061

Abstract(141) PDF(6)

Abstract:
According to the defects shown in the flutter tests of stepped adjusting dynamical pressure in high speed intermittent wind tunnel,such as:long testing time,high gas consump-tion,and short acceptable life of testing models,researches on flutter test technology of continu-ously adjusting dynamical pressure in high-speed intermittent wind tunnels are conducted.Tech-nical problems of flutter test data processing and wind tunnel flow controlling have mainly been solved.The specific approaches are:in the 2.4m×2.4m blow off transonic wind tunnel,fixed Mach number and linear varying total pressure controlling strategies based on movement function are presented,and thus the flow controlling goal of fixed Mach number continuously adjusting dynamical pressure is achieved.The controlling uncertainty of Mach number reaches less than 0.005 without deviation of dynamical pressure.The Pick-Hold method is adopted to set up the subcritical prediction criterion in flutter boundary;according to the characteristic that the recipro-cal of predicting criterion is close to the normal distribution,a parameter estimation method based on the mathematical statistics theory can be used to reduce the diffusive sampling of the prediction criterion and then the accuracy of the subcritical prediction of flutter boundary can be increased.The results of wind tunnel verification test show that the flutter test results of contin-uously adjusting dynamical pressure is in consistent to that of stepped adjusting dynamical pres-sure,and the test technology has reached engineering practical levels;besides,the gas consump-tion is greatly reduced by using flutter test technology of continuously adjusting dynamical pres-sure,and thus it also has good economic benefits.

Investigation of aeroacoustic localization technique in lining test section

Chen Bao, Li Zhoufu, Tan Xiao, Li Yuanshou, Shao Tianshuang, Zhang Xue, Jiang Tao

2015, (5): 78-83. doi: 10.11729/syltlx20150035

Abstract(146) PDF(6)

Abstract:
To meet the requirement of aeroacoustic localization experiment for civil aircrafts like C919 and MA700 in aero-acoustic wind tunnel tests,a liner test section featuring phased ar-ray beamforming algorithm and diagonal removal deconvolution was adopted to deal with the high background noise and flow interference to microphones in the closed test section.MA60 model test was carried out for validation.Test results show that the acoustic liner is in favour of micro-phone phased array and line array installation in the closed test section,and the background noise is reduced to be about 5 ~10dB which is lower than that in traditional closed test sections.The sound pressure level and trend found in the localization tests are reasonable.Judging from the re-sults,FL9 is capable of locating source and taking aeroacoustic experiments of airframe source lo-calization,noise reduction technique validation in the development of civil aircrafts.

Application of PID based on adaptive genetic algorithms in wind velocity control system of wind tunnels

Ni Wenbin, Dong Jingang, Liu Shuwei, He Lihui, Fu Zengliang

2015, (5): 84-89. doi: 10.11729/syltlx20150016

Abstract(253) PDF(13)

Abstract:
In order to accomplish the wind speed control system for a FDxx wind tunnel,a PID parameter setting method based on adaptive online genetic algorithm was designed.In the case of the limited gas source for a wind tunnel test,the algorithm can quickly establish the flow field and ensure the stability time of the flow.First,joint coding is done with these parameters. With elitist strategy adopted in early genetic evolution stage,a non-linear selection method based on roulette selection is introduced in the last period.So optimum individuals are preserved and the population diversity is increased.The fixed value thus would not be exceeded in the dynamic adjustment process.The objective function is set up with the error absolutes and variation rate accompanied by penalty functions.When the fixed value is exceeded,the excess is taken as the optimal.This method has been applied in a field debugging of FDXX wind tunnel.The result shows that it is fast,effective and reliable to use online adaptive genetic algorithms to set the PID control parameters.

Ground experimental method for stratospheric propeller plasma flow control

Chen Qingya, Tian Xihui, Che Xueke, Nie Wansheng, Zhou Siyin

2015, (5): 90-96. doi: 10.11729/syltlx20140140

Abstract(135) PDF(4)

Abstract:
According to the propeller Reynolds-similarity theory and the plasma induced jet similarity theory,the method which is used to study the performance of plasma flow control of high-attitude propeller by ground experiment is put forward based on the blade element theory. First,the propeller geometry and motion parameters are converted to the inflow velocity and an-gle of attack on the blade element.Second,the induced plasma voltage and inflow parameters are determined based on the similarity theory in ground experiment.Finally,the collected experi-mental data is processed to assess the aerodynamic performance of propeller.A high-attitude 20km S1223 airfoil propeller plasma flow control experiment is conducted by this method.It is found that when the propeller revolves at the speed of 300r/min under forward velocity of 5 ~20m/s,the thrust of propeller is increased by 6.6%~10.9% with the high voltage AC input, but at the speed of 600r/min the thrust is reduced by 0.52%~1.7%.

2015 Vol. 29, No. 5