实验流体力学

The progress and challenges of aerodynamics in the bionic flapping-wing micro air vehicle

Yang Wenqing, Song Bifeng, Song Wenping, Chen Lili

2015, (3): 1-10. doi: 10.11729/syltlx2015ty01

Abstract(286) PDF(32)

Abstract:
The bionic micro air vehicle (MAV )has important applications in military and civilian usage.In recent years,researchers over the world have revealed several unique flight mechanisms ,and developed several kinds of bionic micro air vehicles capable of certain flight abil-ities.In this paper,the aerodynamics progress in the bionic MAV is reviewed;also,the opportu-nity and challenges faced in the future are analyzed.At present,compared with the natural flyers,manmade bionic MAV is still clumsy and in a lower level,and thus has a large room for improvement.Many problems need to be tackled.The aerodynamics of low Reynolds number flow in unsteady state is one of the main problems.Since the flow is complex in this regime,the numerical simulation and the wind tunnel experiment can hardly model the situation of true flight.There are four concrete problems:(1 )the Reynolds number of bionic MAV flows is around 103~105 .In this regime,the transition and turbulence are easy to turn up,which makes the flow mechanism complex;(2 )the dynamic aero-elastic problem of flexible wing MAV in flight.In this situation,the scaling law is hard when the size is different for the structure and flow has different reference value.It is an essential problem to establish an accurate simulating model;(3 )the coupling problem of aero-elasticity and flight dynamics in high maneuverable flight;(4)the influence of flight attitude of flapping wing on the flight control system increases the complexity of feedback coupling control algorithm.These multi-disciplinary coupling problems make it a challenge to provide high accurate analysis for and improve the design of the bionic MAV.In the future,by solving the above problems,the bionic MAV should have high maneuver ability and can morph actively,like the natural flyers.

Development and application of molecular tagging velocimetry

Ye Jingfeng, Hu Zhiyun, Liu Jingru, Song Wenyan

2015, (3): 11-17,61. doi: 10.11729/syltlx20140079

Abstract(194) PDF(16)

Abstract:
Molecular tagging velocimetry is a kind of laser diagnostic technique for flow dis-play and velocity measurements.In this paper,the authors introduced the molecular tagging ve-locimetry in detail by analyzing the technique development of tag creating,tag displaying,and data processing.Several application examples of the velocity measurements of supersonic flow, boundary layer flow and the exhaust gas of engine using OH and NO tagging techniques were lis-ted.The problems that the molecular tagging velocimetry has encountered in industrial applica-tion,such as the background in reaction flow,the strong vibration environment and the optical windows restriction,were discussed and analyzed.

Progress in aero-acoustic technology of helicopter

Chen Pingjian, Zhong Weigui, Duan Guangzhan

2015, (3): 18-24. doi: 10.11729/syltlx20140124

Abstract(246) PDF(34)

Abstract:
The status and progress in helicopter aero-acoustic technology is presented,inclu-ding test technology,analysis method and rotor noise control technology.The advanced test technologies such as unsteady pressure measurement,flow field visualization and noise source lo-calization,have been implemented in the acoustic wind tunnel test of rotor noise,which is the es-sential instrument for helicopter aero-acoustic research.Flight test of helicopter aero-acoustic measurements has become a necessary technique in the programs of helicopter noise certification and helicopter noise reduction investigation.With the development of helicopter aero-acoustic noise analysis method,many software tools for rotor noise prediction have been developed and applied in the helicopter design and noise reduction research,based on the solutions of the FW-H equation and Kirchhoff equation.Low noise blade tip is the primary and effective method for heli-copter noise control,and is used widely in helicopter design.Moreover,new technologies such as noise abatement operation and active rotor noise control have been validated by flight test,but have not been used in helicopter design get.Initiated by the demands to design environmentally compatible helicopter,both societies of industry and academia will devote more effort in helicop-ter aero-acoustic technology research.

Liu Lei, Gui Yewei, Du Yanxia, Geng Xiangren, Wang Anling

2015, (3): 25-29. doi: 10.11729/syltlx20140120

Abstract(131) PDF(6)

Abstract:
The performance parameters of thermal protection system (TPS)are essential for the design and optimization of high-speed aircraft.Most of these performance parameters are ob-tained from wind tunnel assessment test.Due to the limitation of the equipment capacity of wind tunnel ,the size of the test model and the flow conditions are very different from the actual flight. The experimental data are not practicable directly and need to be converted to those under actual flight conditions based on the flight-ground conversion method.In this paper,the similarity pa-rameters in the heat conduction equation and thermoelasticity equations are discussed.The wind tunnel environment is also studied.The similarity criterion equations and boundary condition e-quations are obtained.Finally,parts of the similarity parameters in this paper are calculated and analyzed.Based on the results,the wind tunnel test can be adjusted according to this similarity criterion to improve the precision and efficiency of experiments.

Preliminary research on spray nozzle atomization characteristics in icing wind tunnel environment

Fu Cheng, Peng Qiang, Zhang Haiyang, Wang Chao, Wu Shenghao

2015, (3): 30-34. doi: 10.11729/syltlx20140064

Abstract(252) PDF(15)

Abstract:
The icing cloud inside the icing wind tunnel test section is generated by the Spray Bar System (SBS)which is located at the wind tunnel settling chamber.The icing conditions such as the icing cloud liquid water content (LWC)and water droplet size (MVD)are determined by the performance of the spray nozzle of performance on SBS.The enviromental parameters of the icing wind tunnel operation such as the pressure,temperature,wind speed and diameter of liquid droplet can change the final atomization characteristics in the test section.In the 0.3m× 0.2m icing wind tunnel with low pressure spray nozzle testing platform,we used Phase Doppler Interferometer(PDI)to measure the droplet evaporation rate and spray nozzle performance enve-lope in different icing wind tunnel operation environments.The experimental results show that:the icing wind tunnel flow condition can change the MVD when the liquid droplets fly into the test section through the contraction section;when the wind speed,the temperature and Reynold number of liquid droplet increase,the evaporation rate of droplet will also increase;the ambient pressure has an indispensable influence on the MVD and spray nozzle performance envelope;as the ambient pressure reduces,the spray nozzle flow mass-MVD envelope is narrowed down,but the spray nozzle water flow mass is hardly influenced.These experimental results can be used in the icing wind tunnel for icing cloud simulation and uniformity debugging.

Comparison between aerodynamic admittances identified via force and pressure measurement tests

Tan Zhongxu, Zhu Ledong, Xu Ziran, Chen Wei

2015, (3): 35-40. doi: 10.11729/syltlx20140086

Abstract(98) PDF(4)

Abstract:
Aerodynamic admittances are important parameters in buffeting analysis,and often identified via wind tunnel test of force or pressure measurement in turbulent wind field.However, both the natural vibration of the balance-model system and the frequency-response effect of the tubing system for pressure measurement can affect the identified results of aerodynamic admittance.In this study,the aerodynamic admittances of a quasi-flat section were identified via wind tunnel tests of force and pressure measurements in conj unction with a least square method based on a colligated-residue composed of buffeting-force auto-spectrum and cross-spectra be-tween buffeting force and fluctuating wind speeds (simplified as “colligated least square meth-od”).The span-wise incomplete correlation effect of buffeting forces on the sectional model was taken into account in the identification of aerodynamic admittance based on the force measure-ment test.Two cases with and without correcting the frequency-response effect of pressure tub-ing system according to the Bergh-Tij deman’s formulae were considered in the identification of aerodynamic admittance based on the pressure measurement test.On these bases,the influences of the natural vibration of the balance-model system and the frequency-response effect of the pres-sure tubing system on the identified results of the aerodynamic admittances were investigated by observing the discrepancies among the test results and the Sears Function,which is the theoreti-cal aerodynamic admittance of flat plate cross section.The results show that the resonance of bal-ance-model system can significantly amplify the identified results of aerodynamic admittances. Furthermore ,compared with the results of aerodynamic admittances identified via force measure-ment test,those identified via the pressure measurement test are much more reasonable in gener-al,and have much wider ranges of reduced frequency with practicable values,because the natural frequency of pressure tubing system is generally much higher than that of the balance-model sys-tem.Moreover,the values of the identified aerodynamic admittances would drop to some extent within a concerned range of reduced frequency for buffeting analyses of common long span bridges after considering the correction of frequency-response effect of pressure tubing system,because the resonance effect of tube cavity plays an amplifying role on the fluctuating pressure signals with frequencies lower than the resonant frequency of the tube.

Experimental study on motion response of a seaplane on waves

Huang Miao, Wu Bin, Jiang Rong, Jiao Jun

2015, (3): 41-46. doi: 10.11729/syltlx20140104

Abstract(129) PDF(8)

Abstract:
With newly designed test devices and data acquisition mode,a powdered-model-reg-ular-wave experiment of a seaplane is conducted.The changes of the experimental method can ef-fectively eliminate the negative impacts of the step-type signal mutation.Based on the test re-sults,the pitching,heaving motion and overload response variation laws with encounter frequen-cy and wavelength are obtained.The results show that the pitching and heaving motion response curve has a single peak,and the corresponding resonant wavelength varies from 1 .5 to 3 .5 times the hull length;the overload response curve has double peaks,and the first resonant wavelength varies from 1.5 to 3.5 times the hull length,while the second resonant wavelength is about 0.5 times the hull length.Based on these motion properties,the motion response of the full scale seaplane to waves is analyzed,and also some suggestions about the selection of the operational environmental condition are offered.

Experimental investigation on phase split of gas-liquid two-phase flows at a T-junction on a 180°return bend

Yang Limin, Feng Yan, Lyu Jinping, Wang Hong

2015, (3): 47-53. doi: 10.11729/syltlx20140073

Abstract(116) PDF(4)

Abstract:
In order to explore the phase split mechanism of two-phase flow at T-junction,a T-junction on a 180°return bend was employed to provide additional forces,such as centrifugal, gravitational and/or buoyant forces when two-phase mixture flows passing through it.The fac-tors,such as the resultant force at the branch direction,inlet momentums of the two phases,and inlet flow patterns at the phase separation were investigated experimentally.Using air and water as two working fluids,the inlet flow patterns for the two-phase flows were set as bubble and annular flows,respectively,and the inlet tube for the bend was placed vertically upward or downward .The phase split data were measured under varying the inlet flow pattern and gas and/or liquid velocities and the flow pattern transition around the bend and at the T-junction was carefully examined.The results show that under the condition of vertically upward inlet tube and the bub-ble flow pattern,the gas is mainly subjected to buoyant force and the liquid to gravitational force.Thus gas takes off preferentially under the condition of the branch.Increasing gas or liquid velocity is harmful to the gas take-off.Whereas at vertically upward inlet tube and annular flow, the liquid is mainly subjected to centrifugal force,and thus the liquid preferentially takes off from the branch.Increasing gas or liquid velocity is beneficial to the liquid take-off.In the case of vertical-ly downward annular flow,liquid is mainly subjected to downward centrifugal and gravitational forces,thus liquid preferentially takes off from the branch.Increasing gas or liquid velocity is harmful to the liquid take-off since the bubbles entrained in the liquid flow in the branch are in-creased and the liquid drops generated by the gas core at the bend are also increased.That which phase preferentially takes off depends mainly upon the resultant force at the branch direction. The phase split phenomena can be explained by analyzing the resultant forces,the flow pattern, and the momentums of the two phases at the T-junction.

Unsteady pressure measurement around circular cylinder in hypersonic flows using fast response PSP

Xiang Xingju, Xiong Hongliang, Yuan Minglei, Yu Jingbo, Chen Liusheng, Wang Zhidong

2015, (3): 54-61. doi: 10.11729/syltlx20140108

Abstract(108) PDF(16)

Abstract:
The fast response Pressure Sensitive Paint (PSP)was studied to develop the capa-bility of making global pressure measurements under unsteady and short duration flow condi-tions.Fast response PSP is necessary for measuring unsteady flow fields in hypersonic wind tun-nels and short-duration wind tunnels.By the use of the fast response PSP,unsteady flow field can be accurately measured.Various PSP formulations are under continuous development in col-laboration between CAAA and Institute of Chemistry China Academy of Science.These pressure sensitive paints use PtTFPP as luminophore,which is relatively photo-stable:the decay of lumi-nescent intensity with continuous illumination is 1 .5 percent/h.This paint can be sprayable on all kinds of model surfaces.It is durable enough to withstand the aerodynamic forces.With the development of porous PSP,there has been a need for accurate characterization of the response time of PSP.Dynamic calibration methods have been developed to meet this need.Response time of PSP was measured from a step change of pressure created by solenoid valve and pulsating jet. Two dynamic calibration devices were developed to test the response time of PSP.For unsteady calibration the paint was sprayed onto 20 mm × 20 mm aluminum plates.Photo multiplier tube (PMT)was used as the light detector,which is the most critical component in the dynamic cali-bration device.Several fast response PSP was developed and tested.The typical response time of PSP is 0.2ms.The static calibration system was used to get the relation between the pressure and luminescence intensity.PSP samples were installed in a pressure chamber in which both the pres-sure and temperature can be set.The sample was excited by UV light and its photoluminescence was detected by a CCD digital camera.The experiment was conducted at different pressures and temperatures.After data processing,the relationship between the luminescence intensity and pressure can be obtained.To demonstrate the capability of PSP for pressure measurements in hy-personic wind tunnel,a cylinder mounted on a flat plate was tested in a Mach 5 hypersonic wind tunnel.The experiment was conducted in the blow down hypersonic wind tunnel FD-03 of China Academy of Aerospace Aerodynamics (CAAA).The diameter of circular cylinder is 25mm.The pressure on the plate surface was measured by several pressure taps simultaneously.The temper-ature of the model was detected by a Pt100 temperature sensor in real time.A 200-mm-diameter observation window on the ceiling was used as the optical access.Two 450W xenon lamps with bandpass filter (365±10 nm)were used for excitation light.The emission from the PSP was de-tected by photron high-speed camera SA5 with 12-bit intensity resolution.A bandpass filter (650 ±10 nm)was placed in front of the camera lens.The surface pressure distributions were ac-quired.Unsteady pressure behavior around the cylinder measured by the unsteady PSP was shown clearly.The pressure distribution results were obtained at Ma= 5 ,and the unsteady PSP measurement frame rate was 250 frames/s.A detailed pressure distribution pattern of complex flow phenomena including shock wave/shock wave interactions could be clearly measured with PSP.It was confirmed that fast response PSP could be used for quantitative unsteady pressure distribution measurements in hypersonic wind tunnel.

Measurements of gas temperature and atomic oxygen density in the arc-heated wind tunnel based on TDLAS

Ou Dongbin, Chen Lianzhong, Dong Yonghui, Lin Xin, Li Fei, Yu Xilong

2015, (3): 62-67. doi: 10.11729/syltlx20140071

Abstract(223) PDF(29)

Abstract:
Large-scale,high-enthalpy arc heated wind tunnels are the most reliable ground test facilities to test thermal protection materials and heat shield structures for space vehicles. Flow conditions in the facility need to be monitored.Currently,the facility conditions are defined using either the anticipated surface temperature with an assuming emissivity or the expected heat flux level.While this is useful to evaluate relative performance of the facility,it is not sufficient for quantitative measurement of the flow conditions.Temperature is one of the most important thermodynamic quantities in determining arc heated wind tunnel because it is a key parameter in determining arc-heater operating status and chemical reactions.Therefore,the development of accurate quantitative diagnostic techniques is necessary for better understanding the complex physics involved in the arc heated wind tunnel.The design of a tunable diode laser absorption spectroscopy (TDLAS)system to probe gas parameters during a bow shock wave ahead of a wa-ter cooled copper cylinder is presented in this paper.TDLAS is an effective method for measuring gas temperature and concentration in many fields due to its advantage of non-intrusive,high sensitivity, gas-specific and quick response.In our studies,an atomic oxygen absorption line near 777.2nm is utilized for detecting the arc-heated plasma using scanned-wavelength direct absorption mode with 100Hz repetition rate.The value of temperature is inferred directly from the Doppler broadening component of the absorption lineshape.Moreover,the number density of atomic oxygen is also determined through the integrated absorbance assuming local thermal equilibrium conditions. The agreement of the experimental observations and theoretical calculations shows that the ther-mal equilibrium assumption is valid.The current experimental results of this study illustrate the high potential of TDLAS measurements for routine and economical monitoring of arc heated wind tunnel operating status (gas temperature)as well as the time-resolved flow conditions in front of the model.

Research on particle image velocimetry based on optical flow

Wang Hongwei, Huang Zhan

2015, (3): 68-75. doi: 10.11729/syltlx20140115

Abstract(134) PDF(11)

Abstract:
As a new aerodynamics experimental technique,optical flow test technique gradual-ly attracts more and more attention due to its advantages in vector field measurement with pixel scale resolution and strong smoothness ability.By means of scalar constraint equation combined with smoothness constraint condition,optical flow test technique can measure global velocity vec-tor field with high space resolution.In this paper,the integration minimization optical flow ve-locimetry theory and algorithm were firstly studied and programmed by C++;then,in order to verify the accuracy of the optical flow algorithm,three groups of grayscale images shifted by giv-en displacements were used for processing by the optical flow algorithm program and the result can be used to guide how to obtain high-precision optical flow calculation result in the actual measurement applications;at last,backward step verification experiment,in which tracer parti-cle images were acquired by high speed camera and velocity vector field was calculated by optical flow algorithm,was completed in a small wind tunnel.The result calculated by optical flow algo-rithm was compared with the result calculated by PIV′s cross-correlation algorithm,which shows that optical flow test technique possesses the advantages of pixel scale resolution.

Research on a micro-rolling-moment six-component strain gauge balance of composite structure

Wang Yuhua, Liu Wei, Xie Bin, Zhang Yue

2015, (3): 76-79,98. doi: 10.11729/syltlx20140087

Abstract(163) PDF(5)

Abstract:
Rolling-moment measurement at micro level is extremely important for wind tunnel testing.Compared to conventional force tests,micro-rolling-moment measurement test is charac-terized by small rolling moment loading whose value of quantity is below 0.5N·m,and an obvi-ous difference between rolling moment load and other aerodynamic loads in the value of quantity. It is a great challenge to design a six-component strain gauge balance of appropriate structure for that purpose.To solve this problem,efforts were made to optimize the balance structure and the concept of composite six-component balance was developed and realized,which has reduced the measurement deviation (Δmx0<1.1 ×10-6 )and has addressed the configuration contradictions. In this paper,key techniques and primary technical measures for the newly-designed balance are introduced,with an account of the results of balance analysis and calculation,static calibration and test measurements.

Design and numerical simulation of an elliptical nozzle

Long Yongsheng, Hu Zhenzhen, Yuan Jie, Li Haiyan

2015, (3): 80-86. doi: 10.11729/syltlx20150045

Abstract(259) PDF(18)

Abstract:
A method is proposed for the design of an elliptical nozzle.The flow fields of the elliptical nozzle and the rectangle one are analyzed and compared.The numerical simulations indi-cate that the exit Mach number of the elliptical nozzle is greater than that of the rectangle one un-der the same conditions,i.e.the same reservoir parameters,length and exit area.The turbu-lence and high temperature real gas effects reduce the effective area ratio and change the expan-sion waves.A fine uniform outflow can be obtained by choosing an appropriate location of the ex-it.As a special device for the hypersonic wind tunnel experiments,the elliptical nozzle can im-prove the simulation ability of the wind tunnel by its high efficiency in using the energy of the heater.This nozzle can be applied to perform the thermal protection experimental researches on large-scale models with flat-like leading edge,helm or wing and on large length-width ratio scramjet engines.

A new ground test method for near space propeller

Li Xile, Li Guangjia, Zhou Bo, Zhu Wenguo, Sun Kaijun

2015, (3): 87-92. doi: 10.11729/syltlx20140138

Abstract(187) PDF(10)

Abstract:
A new experimental technology for testing the aerodynamic performance of near space propeller by a railcar on the ground is proposed,in which the advance speed of the propeller is controlled by a high accuracy railcar,and the rotation speed of the propeller is controlled by a servo-electromotor.According to the equal Reynolds number and equal advance ratio similarity criterion,ground experiments including thrust and torque measurement were carried out to inves-tigate the designed near space propeller aerodynamic characteristics at different flight altitudes, and the experimental data was compared with computational results by strip theory and CFD method.The results indicate that:(1 )because the Mach number at the tip of the propeller is lower,the equal Reynolds number and equal advance ratio similarity criterion is appropriate for the designed near space propeller experiment on the ground;(2 )the ground experimental data of propeller at different altitudes agree well with computational results,and thus it is proved that the new experimental method is feasible and can provide a reference for similar propeller tests.

Numerical and experimental researches on contraction boundary correction for pilot aeroacoustic wind tunnel

Liu Weihong, Yao Lei, Yu Yongsheng, Lyu Jinlei, Qu Xiaoli, Zhu Bo

2015, (3): 93-98. doi: 10.11729/syltlx20140067

Abstract(156) PDF(4)

Abstract:
On the basis of the master curve of boundary layer displacement thickness for low speed wind tunnel contraction obtained from numerical research,the distribution of the displace-ment thicknessδ* for the pilot aeroacoustic wind tunnel(PAWT)’s contraction is derived.Ac-cordingly,we redesigned the contraction contour,gave the deviation after correction,fabricated the test article,and conducted the numerical simulation and experimental study.The numerical results show that,although the boundary layer of the contraction was very thin and the maxi-mumδ* was only 0 .5% or so of the test section hydraulic diameter,the correction effect was re-markable.After the correction,for both open and closed test sections,the dynamic pressure non-uniformity was reduced,the flow-deviation angle decreased,and the flow field quality was im-proved.At the contraction exit,the near wall velocity was overshoot due to the reverse pressure gradient.But after entering the straightness section,the dynamic pressure non-uniformity and the flow angle decreased sharply.After the contraction,there is a straight section whose length is 1 6 .7% of contraction,which is very helpful for improving the flowfield quality.Using mova-ble measuring device,pitot tube and hotwire anemometer,we measured the dynamic pressure and velocity before and after the correction.The measuredδ* coincides with the theoreticalδ*, and the effect of boundary correction is verified experimentally.Based on the measured velocity distribution,it can be inferred that the boundary layer in the contraction of PAWT is laminar, without transition from laminar to turbulent flow.

Study on gas natural frequency of pipeline system with air cooler

Han Wenlong, Wei Guo, Han Shengliang, Bai Changqing

2015, (3): 99-103. doi: 10.11729/syltlx20140106

Abstract(141) PDF(2)

Abstract:
A simple air cooler model is designed and manufactured based on conventional air coolers used in engineering and the national standard of GB/T-15386-94.The pipeline with the air cooler experimental system is constructed,and the fluid dynamics of the piping system is mod-eled.Comparing the numerical results with test data,it can be found that both the experimental method of frequency sweep and the numerical simulation method of frequency response are cor-rect and reasonable.The parametric model of the air cooler as a special pipe component is pro-posed based on the results of experiment and simulation,which is named as “Volume-Pipe-Vol-ume”model.It provide a direct and effective method for calculating the gas natural frequency of pipeline system with air cooler.

Study on influencing factors and estimation method of Helmholtz harmonic frequency in transonic compressor test system

He Lei, Pan Tianyu, Li Qiushi

2015, (3): 104-109. doi: 10.11729/syltlx20140091

Abstract(111) PDF(2)

Abstract:
Compressor testing facility is one of the fundamental and imperative experimental apparatus when carrying out experiments to investigate phenomena occurring within the compres-sor.In this paper,experiments have been carried out on the complex transonic compressor tes-ting facility in Beihang University to analyze the influence of the systematic Helmholtz harmonic frequency on this specific testing facility.Several modifications have been made to this compres-sor testing facility in Beihang University to accommodate the experiments.Firstly,the settling chamber,screen and other parts have been removed from this testing facility.In addition,the geometry of the compressor testing facility has been adjusted for this experiment.Modified compressor testing facility has been modeled using Duct-Compressor-Plenum model theory;cal-culations on estimating the effect of the systematic Helmholtz harmonic frequency have been con-ducted and investigated.Final results indicate that the settling chamber at the inlet cannot affect the systematic Helmholtz harmonic frequency,but can improve the uniformity of the flow and minimize the turbulence level.It can be concluded that the Duct-Compressor-Plenum model should not be applied to the testing facility when conducting experiments on it.

2015 Vol. 29, No. 3