实验流体力学

Review of the state-of-art and aerodynamic technology of X-37B

Sun Zongxiang, Tang Zhigong, Chen Xilan, Zhong Ping, Liu Xiaobo

2015, (1): 1-14,24. doi: 10.11729/syltlx20140132

Abstract(377) PDF(71)

Abstract:
The research and development of X-37B has attracted high attention in recent years.It is significant to investigate the trans-atmospheric vehicle from the aspect of aerodynamic technology.In this paper,the development history of X-37B is introduced.Its strategic utility is discussed,and some key aerodynamic technologies are reviewed,including the optimization de-sign of the aerodynamic configuration,the compound control system design of the aero-surfaces/RCS/OMS,the thermal protection technology,aero-assisted orbital transfer.The progress based on the three major methods of aerodynamics research is also reviewed.Finally,experience and lessons from X-37B are summarized briefly.

Three-dimensional vorticity and heat transport in a circular cylinder wake using phase-averaging method

Cao Huali, Chen Jiangang, Zhou Tongming, Zhou Yu

2015, (1): 15-24. doi: 10.11729/syltlx20140062

Abstract(281) PDF(47)

Abstract:
This work aims to provide insight into the three-dimensional aspects of momentum and heat transport in a turbulent cylinder wake.All three components of the velocity and vorticity vectors, along with the fluctuating temperatures,were simultaneously measured with an 8 hot-wire vorticity probe and four cold-wire probes.Measurement was made at x/d= 10~40 at a Reynolds number of 2540.A phase-averaging technique has been developed to detect reliably the coherent events,thus allo-wing the coherent contributions from various quantities associated with the vectors as well as passive scalar fields to be quantified accurately.The results show that there is a close similarity between the con-tour of spanwise vorticity and that of the streamwise vorticity at x/d= 1 0 ,due to the strong rolling up effect of the spanwise vortex.As x/d increases,the similarity betweenωx andωy contours can still be observed,resulting from the contributions of the rib-like structures.It exhibits significant three-dimensional qualities of the vortex structure in the near wake.While the coherent heat flux is largely as-sociated with the spanwise vortex rolls,the incoherent (or ‘remainder’)heat flux occurs between two successive opposite-signed vortices,rather than in the saddle region.Due to the combined effect of the spanwise vortex and the rib-like structure,the spanwise heat flux behaves quite differently at different locations.The w~*~θ* contour inside the negatively signed vortex is close to the vortex center,while the w~*~θ* inside the positive one is stretched to the saddle point aligning with the diverging separatrix.As x/d increases,the negative w~*~θ* contour becomes dominant and moves towards the vortex border, which contributes to the net heat transport out of the spanwise vortex.In addition,coherent motion con-tributes similarly to the longitudinal and spanwise heat flux components.

An experimental investigation on the vitiation effects of hypersonic testing of aerothermal behaviors

Jiang Hongliang, Liu Kunwei, Jin Yi, Zhu Yujian, Yang Jiming, Wu Yingchuan

2015, (1): 25-30. doi: 10.11729/syltlx20140016

Abstract(136) PDF(5)

Abstract:
For ground tests in a combustion-heated wind tunnel,the composition of the tes-ting gas is different from that of the air,which may cause some unexpected deviations and result in more uncertainties.An experimental investigation on the vitiation effects of hypersonic testing is carried out with special focus on the aerothermal behaviors of the model flow.The experiments are conducted in a shock tunnel and the related combustion-heated wind tunnel flow conditions are simulated by adj usting the strengths of shock waves and adding specific mole fractions of contam-inations (H2 O and CO2 ).A couple of simplified wedge models with different deflection angles are used to characterize the typical compression of the flow by the vehicle model.The static tem-peratures of the wedge model flow under groups of conditions are obtained through tunable diode laser absorption spectroscopy (TDLAS)measurement system.The results indicate that the vitia-tion effects depend not only on the fractions of contaminants,but also strongly related to the freestream static temperature as well as the compression process of the model flow.A low tem-perature incoming flow with small compression angle is favorable for reducing the vitiation effects.On the other hand,if the combined interaction of the flow with the compression wall is so severe that the resulted static temperature is increased to a certain level,an obvious depend-ence of vitiation effects on the contaminations are readily observed.

Evaluation of arc-heated wind-tunnel operation in CO2 atmosphere

Zhu Chao, Chen Dejiang, Zhou Wei, Du Baihe, Yao Feng

2015, (1): 31-36. doi: 10.11729/syltlx20140019

Abstract(188) PDF(8)

Abstract:
The main interest of this study is to investigate the performance of the arc-heated wind tunnel using CO2 as the test gas in order to develop heat shield materials for entering Venus and Mars atmospheres which are mainly composed of CO2 .Firstly,the mixture composition e-quilibrium of the CO2 atmospheres for a range of temperatures and pressures has been studied via the equilibrium constant method.Then,numerical simulations of the flow along the facility noz-zle have been performed using a one-dimensional isentropic method with and without freezing. The stagnation point parameters at the exit of the nozzle and theoretical performance map of the arc-heated wind tunnel with CO2 atmospheres have been calculated with one-dimensional method at the equilibrium with and without freezing,based on air envelope and neglecting the effect of arc-heater efficiency.It indicates that since the mole fraction of carbon in the arc-heated flow is as high as 30%,a large amount of carbon can be deposited onto the inside of the arc-heated wind tunnel,which can reduce the performance of insulation and heat conduction.There is a large a-mount of explosive gas CO at the exit of the nozzle no matter whether the flow is freezing or not, whose mole fraction can be as high as 50%.Therefore,it is suggested that all tests in the arc-heated wind tunnel for the simulation of CO2 atmospheres should be carried out using an addition-al inj ection gas such of N2 in the diffuser to deactivate the produced CO in order to protect the vacuum pump system and ensure the safety of people.

Experimental study on a novel method for vertical tail buffet suppression

Zhang Qing, Hua Ruhao, Ye Zhengyin

2015, (1): 37-42. doi: 10.11729/syltlx20140020

Abstract(144) PDF(4)

Abstract:
The twin tails of the modern high performance fighter aircrafts with delta wing/twin vertical tails configuration generally experience significant dynamic load due to aerodynamic buffet caused by highly unsteady vortex breakdown flow.This paper proposes a new type of buf-fet alleviation method by solid static or oscillating bulges attached on the forebody of a delta wing model,and conducts wind tunnel experiment for the model which consists of a sharp-edged,70-degree leading edge sweep delta wing,and twin 31°leading edge sweep vertical tails.The model has been tested at 10m/s and 20m/s of free stream velocity,and at angle of attack ranging from 20°to 50°with an interval of 2°in the low-speed wind tunnel at Northwestern Polytechnical Uni-versity.According to the self-induced theory proposed by experts from University of Washing-ton,the bulges attached on the forebody of a delta wing would twist and kink the vortex core, change the vortex trajectory after the bulge,delay the vortex breakdown position,and decrease the fluctuating level of the flow around the twin vertical tails.Thus the goal of buffeting suppres-sion is achieved.This study aims at investigating the buffet alleviation effect of the static or vi-brating bulges attached on the forebody surface of the model.Two pairs of half bridged strain gauges are employed for the measurement of unsteady root strain on the vertical tails,with one pair on each side.The experimental results show that both static and vibrating bulges behave positively as a novel tool to alleviate tail buffet,and the alleviation effect correlates with the vi-brating frequency.Besides,the bulge on one side can only alleviate the buffeting for the tail of the same side,and it has no obvious alleviation effect for the tail on the opposite side.Results of spectral analysis prove that the bulges used in this experiment could alleviate tail buffeting,but they do not change the dominant frequency of the oscillation of the tails in the vortex breakdown flow.

Study on lateral stability of hypersonic lifting-configurations

Gao Qing, Li Jianhua, Li Qian

2015, (1): 43-48. doi: 10.11729/syltlx20130107

Abstract(157) PDF(13)

Abstract:
Hypersonic lifting-configurations have high lift-drag ratio,but are vulnerable to in-stability.Researches show that compared to the directional stability,the lateral stability is even weaker. To have a deeper understanding of the lateral stability of hypersonic lifting-configurations,wind-tunnel tests of roll non-steady aerodynamics for two typical hypersonic lifting-configurations are carried out in FD-07 in China Academy of Aerospace Aerodynamics.The tests adopt free-oscillation method.The test Mach numbers are 5 and 6 ,and the corresponding Reynolds numbers per unit length are 2.3 ×107 and 2.0 ×107 ,respectively.During the roll dynamic stability tests of the first test model,the model vibrated violently even when the angle of attack was small.This is possibly provoked by the asymmetric transition from the small transverse flow around the nose of model.Subsequent research adopts longitudinal strips to generate symmetric transition at the fore-body of the model.Test results confirm that the adoption of longitudinal strips could indeed stimulate symmetric transition of lateral flow and strengthen the lateral stability of hypersonic aircrafts at the same time.During the wind-tunnel tests of the second test model,the oscillations of the model presented a certain multi-frequency and periodical characteristics.Spectrum analysis of roll vibration data under several different flow conditions show that there are three main vibra-tion frequencies apart from the mechanical vibration frequency.It indicates that there are three characteristic lengths in the hypersonic lifting-configurations flow field.In other words,there are three scales of lateral separation or transition.A model of roll moment is established in this paper where the roll moment is expressed as the sum of cosine of the three vibration frequencies.The comparison between the results obtained from this model and the corresponding aerodynamic test data shows that this model can capture the primary tendency of the test curve and cover the main magnitude domain of the roll aerodynamic moment.

Wind characteristics of grid-generated wind field along the wind tunnel

Yan Lei, Zhu Ledong

2015, (1): 49-54. doi: 10.11729/syltlx20140075

Abstract(164) PDF(10)

Abstract:
Grid-generated wind fields are commonly applied in various wind tunnel tests to ob-tain aerodynamic parameters of flexible bridges.In this work,wind characteristics of grid-gener-ated wind field were investigated at different distances from the grid section along the wind tun-nel.The wind characteristics principally depend on the distance,the thickness of slat and the length of the unit grid side.The results indicate that the mean wind velocity descends steeply and soon afterwards steadies with the distance.The total turbulent energy declines and the dominant energy migrates to the higher frequency region with the distance:the turbulence intensity de-clines and the integral length scale increases;non-dimensional power-spectral density forms and non-dimensional frequencies corresponding to the peak value remain unchanged,but the peak val-ues decline.Two specific turbulent conditions were adjusted according to these contributing fac-tors:similar turbulence intensities with different integral length scales;similar integral length scales with different turbulence intensities,founding the basis to investigate the effects of main wind characteristics on the aeroelastic parameters.

The computational and experimental investigation on winglets of a low speed aircraft

Liu Yi, Zhao Xiaoxia, Jiang Zonghui, Ren Qingzhu

2015, (1): 55-59. doi: 10.11729/syltlx20130039

Abstract(218) PDF(17)

Abstract:
An aircraft with four turbo-propeller engines is characterized by low speed and relative high cruise lift coefficient.Winglets are utilized to improve the flow condition around the wing tips and increase the lift-to-drag ratio.CFD calculation and wind tunnel tests show that the lift-to-drag ratio at endurance cruise can be increased by 8%,while the lift-to-drag ratio at range cruise can be increased by 4.8% after the optimization of geometric parameters.The results of CFD simulation about the aerodynamic characteristics of the winglet agree well with wind tunnel test results, which could be a convenient and economic method for further optimization of winglet geometry.

Study on prediction of ground effect test data

Fang Yue, Zhou Zhiyu, Zhang Lianhe

2015, (1): 60-65. doi: 10.11729/syltlx20130120

Abstract(133) PDF(4)

Abstract:
Based on the incompressible potential flows theory of low speed wind tunnel test, for the test of aircraft ground effect,a method is proposed to calculate and obtain the correspond-ing data for different floor heights of floor from the test data without the floor.The validity of the method is demonstrated by comparing the calculated results with the test data.Meanwhile, correcting the calculated results corresponding to existing test data with the floor can decrease the error of the data predicted by the method.

The experimental research on a flow control device of horizontal tail

Ouyang Shaoxiu, Liu Yi, Zhao Xiaoxia

2015, (1): 66-70. doi: 10.11729/syltlx20130119

Abstract(229) PDF(2)

Abstract:
The aircraft featuring high wing and low horizontal tail encountered local flow sepa-ration at the lower surface of the horizontal tail near the root,which manifests itself as aircraft vibration and abnormal pitching moment.The proposed solution is to install a pair of winglets of small aspect ratio and reversed camber at 0.12 root chord ahead of and 0.30 root chord below the horizontal tail.The winglets function as vortex generator/guiding vane,which enhance the ener-gy exchange between the boundary layer and the outer flow in the separation zone,and also re-duce the local absolute angle of attack of the root section of horizontal tail by the induced up-wash.The numerical simulation and wind tunnel tests reveal that the optimized vortex generator can reduce the separation area by 50%,and delay the starting angle of pitching moment crank by more than 4°.Therefore,the problem of local separation is solved by relatively minor cost of per-formance and weight,and the boundary of flight is enlarged.

Research and development of a compact TDLAS system to measure scramj et combustion temperature

Yao Lu, Liu Wenqing, Kan Ruifeng, Xu Zhenyu, Ruan jun, Wang Liao, Jiang Qiang

2015, (1): 71-76. doi: 10.11729/syltlx20140025

Abstract(265) PDF(36)

Abstract:
Advanced research on air-breathing engine development requires sensitive tech-niques to monitor the temperature distribution in the engine,gas flow fields distribution in the combustion reactant and product concentrations to validate combustion theoretical models and in the engine designs.Moreover,the real time acquisition of these parameters can be utilized to con-trol the working status of the engine to optimize the combustion efficiency.Because of its com-pactness,high sensitivity,fast response and non-intruding measurement feature,the tunable di-ode laser absorption spectroscopy (TDLAS )has been applied by many research institutes in tough in-flight environment,such as high temperature,high speed and violent vibration.In this paper,some electronic key techniques in the hypersonic research program HIFiRE are introduced and our design on compact sensors and some progresses are presented.It has been proved that this system can work stably in in-situ measurement and the compact design (volume of 30×15× 10cm3 ,mass<5kg,power<10W)can provide a reference for the in-flight system in the future.

Research on density measurement based on background oriented schlieren method

Zhang Jun, Xu Di, Zhang Long

2015, (1): 77-82. doi: 10.11729/syltlx20140029

Abstract(308) PDF(42)

Abstract:
Background Oriented Schlieren method (BOS )is a new technique for flow field measurement based on image with remarkable advantages,such as a big field of view,non-intru-sive,and quantitative measurement.It has extensive application prospects in flow field measure-ment.The BOS experimental setup mainly consists of a structured background pattern of random dots,a LED light source and a CCD camera.It needs two images.One is obtained without the density gradient effect as the reference image.The other one is obtained when there is disturb-ance in the flow and is stored as the refracted image.The displacement of the background dots is extracted by performing mathematical correlation analysis on a cluster of particles within each in-terrogation region between the two frames.The displacement vector field represents the gradient of the refractive index which is further integrated to calculate the line-of-sight integrated refrac-tion index via the solution of Poisson equation.This paper describes the implementation of the BOS technique to realize the quantitative visualization of the density in a flow.The basic principle of BOS is expatiated,and the sensitivity and resolution are analyzed.It is shown that the shift of the background dots and the sensitivity increase with increasing distance of the background field from the object of interest.But on the other hand,improving the sensitivity means reducing the physical resolution,as the interrogation size used in the correlation algorithm would have to be correspondingly larger.And the aero optics effect is getting more prominent at the same time. According to the principle of BOS,the background dot pattern is designed.In the experiment, the size of dots is about 3 pixels.In the later experiment,the dot pattern fits well with the dis-placement field’s extracting algorithm.And also a density measure system is constructed.Based on the flame flow and jet flow,through the detection of the deflection of a number of light beams passing the flow field,the density depending on the refractivity is obtained.And the preliminary results for the flame flow and the typical jet flow are presented,such as the refractive index field, the density field,and the temperature field.The experimental results show that the density and temperature distribution can be obtained quantitatively by BOS method expediently,effectively and in a compact way.

A new method for improving the measurement sensitivity of wind tunnel balance

Wang Huilun, Xie Yajun, Jiang Yajun

2015, (1): 83-86,91. doi: 10.11729/syltlx20140003

Abstract(137) PDF(10)

Abstract:
The sensitivity of traditional measurement of small scope aerodynamic force is not very high.Aiming at this problem,this paper introduces a new measurement method:Displace-ment measurement method.It means setting two grooves at the same place as where the tradi-tional gauges are pasted,then measuring the displacement of the grooves as it changs when the grooves are loaded to get the balance formula.Here take three kinds of single component bal-ances as an example:One traditional strain balance and two kinds of the displacement balances with different grooves.The traditional balance and the displacement balance with 2mm grooves are pasted with two kinds of strain gauges,which are the optical fiber strain gauge and the strain gauge respectively,to compare the performance of both the gauges and the measurement meth-ods.And an optical fiber strain gauge is used in the displacement balance with 1mm grooves to compare the different sensitivity caused by different depths of the grooves.The static calibration test and the finite element simulation are carried out,and we can draw conclusions as follows:The new measurement method can improve the sensitivity compared to the traditional methods, and the deeper the groove is,the higher the sensitivity becomes.For example,the sensitivity of the new balance with 2mm deep grooves is improved by 3 times compared to the traditional strain balance,1.57 times compared to the 1mm deep grooves.The accuracy of the new balance with 1mm deep grooves is 0.02%,meeting the accuracy requirements.The accuracy of the balance with 2mm deep grooves is 0.09%.It thus shows that increasing the depth of the grooves would lower the accuracy,which may be caused by the decrease of the rigidity of the balance.Therefore the size of the grooves should be chosen carefully.This paper provides a new idea for small scope aerodynamic force measurement.

Aberrance and rectification of a round pipe for flow field visualization

Yue Maoxiong, Xie Feng, Zhang Jin, Yuan Qiang, Zhang Long

2015, (1): 87-91. doi: 10.11729/syltlx20140014

Abstract(198) PDF(10)

Abstract:
When the flow field in a circular-section pipe is visualized,there exists optical aber-ration along the radii of the pipe,which makes the effective range of flow field smaller.The aber-ration must be calibrated in order to get a bigger view.Commonly a cylindrical len with reverse foci to that of the pipe wall is used to calibrate the distortion.Therefore the design of the calibra-tion cylinder lens is the key.Firstly we calculate the foci of the half-wall of the circular-section pipe,and the other side of the pipe is the same as this side.Then the foci of the calibration cylin-der len is obtained.It is found that the calibration effect of a cylinder len with the traditional pla-no-convex cross section can not meet the requirement.So the foci of the len is recalculated in ZE-MAX software by fixing the distance between the pipe and the len,and then adjusting the two curvatures of len until the output rays are almost parallel in 80% range.The result shows that the optimal cross section takes the form of positive meniscus.After that,we manufactured two glass pipes and two pieces of calibration cylinder lens.Then the result of static state demarcation by grid imaging proves the validity of this method.Compared to the traditional method,this method is more accurate and extends the effective flow field range to more than 80%.Dynamic result is given by the high speed focusing schlieren way.This research has reference signification for flow field visualization in round pipes with a thick wall.

Key technologies study of fluorescent mini-tuft application in the low speed wind tunnel tests

Hui Zenghong, Hou Jinyu, Deng Lei

2015, (1): 92-96. doi: 10.11729/syltlx20130117

Abstract(226) PDF(16)

Abstract:
Fluorescent mini-tuft method is a surface flow visualization technology using mini-tuft with fluorescent material to visualize the flow characteristics under the UV light of specific wavelength.This method can reduce the disturbance of the tufts to the flow and give more accu-rate flow information.In this paper,the key technologies (including the making and sticking method of the mini-tufts,choosing the wavelength of UV lights and taking photos,etc.)of fluo-rescent mini-tuft method are investigated based on a high-lift device wind tunnel test of a certain civil aircraft in NF-3 low speed wind tunnel of NWPU.The results show that,(1)the flow pat-terns at different angles of attack are clear and intuitive,and the developments of the flow states with the angle of attack are shown,(2 )the flow state and range can be easily read in detail from the flow patterns,(3)compared with the fluorescent oil flow tests,the results are relatively sim-ilar under the same experimental conditions.It shows that the fluorescent mini-tuft method can exactly display the flow field.The flow visualization results agree well with the force measure-ment experiments and thus can interpret the force measurement results.

Research on the data processing of unsteady large-amplitude-oscillation experiment

Jiang Yong, Sun Haisheng, Shen Zhihong, Liu Zhitao, Zhang Haiyou

2015, (1): 97-102. doi: 10.11729/syltlx20140017

Abstract(186) PDF(2)

Abstract:
Removing the noise in the experimental data signals and aligning the angle and force signal sequences of the initial data and the test data are the two key issues that remain to be re-solved in the large-amplitude-oscillation test.The basic principle of all-phase digital filtering and the method of processing unsteady experimental data are introduced.The theoretical formula of all-phase data processing is derived in detail.Spectrum analysis of each channel of the balance is used to choose the cutoff frequency in the digital filtering process.The three methods of moving phase,interpolating fitting and Moving Least Square(MLS)fitting are studied in detail for alig-ning the initial data with the test data.The experimental results obtained by the three methods are compared.The results show that all-phase digital filtering can remove the noise in the experi-mental signal data successfully and reduce the signal phase and amplitude distortion.The experi-mental results obtained by the three different methods are consistent and reasonable.

Application of Kalman filtering in continuous dynamic traj ectory simulation technique of the captive traj ectory system used in a transonic wind tunnel

Wang Fei, Zhu Rusong, Zhang Junsheng

2015, (1): 103-108. doi: 10.11729/syltlx20120029

Abstract(139) PDF(4)

Abstract:
The flying traj ectory simulation of the store after being separated from the mother plane is an advanced and difficult technique in wind tunnel test.In this paper,the continuous dy-namic traj ectory simulation technique is studied in the Captive Traj ectory System (CTS)used in a transonic wind tunnel.This paper initially introduces the dynamic trajectory predicting principle. Then,the specific steps of the coordinated control method of continuous dynamic trajectory simu-lation are amply described.The algorithm and constraint condition of the coordinated control and the buffering coordinated control are also discussed.Finally,the Taylor mean value theorem is applied to build a Kalman filtering model to resolve the conflict between filtering delay and accu-racy requirements.After choosing appropriate parameter,the Kalman filtering is used to process the balance signal dynamically and in real time,and the comparison between the continuous dy-namic control process and the move-and-stop control process is carried out.The wind tunnel CTS test result shows that the Kalman filtering can reduce the signal fluctuation greatly,meet the re-al-time requirements of CTS,and dynamic separation trajectory of the continuous dynamic con-trol process metches well with the one of the move-and-stop cortrol,while the wind tunnel CTS test efficiency has also been considerably improved.

2015 Vol. 29, No. 1