实验流体力学

The problems and progress in the experimental study of Micro/Nano-scaleflow

Li Zhanhua, Zheng Xu

2014, (3): 1-11. doi: 10.11729/syltlx20140018

Abstract(369) PDF(30)

Abstract:
The micro/nanoscale experimental fluid mechanics studies the fluid flow with the typical dimension from about 1mm to 1nm,which is also the transition range from the macro-scopic flow to molecular motion.The combination of the two classical theories:the continuum mechanics and the quantum mechanics,pusts forward some basic theoretical problems like the validity of the continuity hypothesis and the boundary slip.In the mean time,due to the coupling of the liquid/solid/gas phases in micro/nanoscale,it is worthy considering the influence of inter-facial chemistry and electric properties on the flow.Therefore,micro/nano experimental devices should integrate force and electricity measurements,and require a nanometer measuring space resolution,a pN force precision and a nano-second time resolution.This paper focuses on the problems of validity of the continuity hypothesis,boundary slip,Brownian motion of micro/nano-particles and micro-vortex flow,and introduces the progresses and difficulties of micro/nano flow measurement by Micro/Nano PIV and micro/nanoscale flow visualization using trac-ers.Up to date,the study of micro/nano flow is still following the idea of “miniaturization”of the classical fluid mechanics measurement,however,the nano flow measurement urgently needs new techniques and methods.

Progress in absorption spectroscopy diagnosis techniques for combustion flowfields

Hong Yanji

2014, (3): 12-25. doi: 10.11729/syltlx2014ty02

Abstract(189) PDF(17)

Abstract:
Tunable diode laser absorption spectroscopy (TDLAS),a line-of-sight technology, is used to measure the temperature,velocity,concentration and other parameters in the flow field.As a fast and efficient diagnostic tool,TDLAS sensors have wide applications in the devel-opment of the combustion and propulsion system.TDLAS sensors play more and more important role in the improvement of the system performance.When new concept propulsion appears,the sensors face new challenge,at the same time,relevant technology have been improved.The de-velopment of the TDLAS technique,applications in the combustion diagnosis and enormous po-tential have been summarized.This review can provide enlightenment and help for the research-ers in this field.

Scale effects on the starting characteristics of a 2D hypersonic inlet

Ling Gang, Li Zhufei, Xiao Fengshou, Jiang Hongliang, Liu Kunwei, Gao Wenzhi, Yang Jiming

2014, (3): 26-31. doi: 10.11729/syltlx20130115

Abstract(164) PDF(11)

Abstract:
A combined numerical and experimental investigation was carried out for the self-starting characteristics of a 2D hypersonic inlet,with a special focus on the comparison between different scale models.The numerical results show that the self-starting capability is decreased when the model scale is reduced under the same unit Reynolds number condition,during which the corresponding self-starting Mach number may go up remarkably.It was also found that the inlet flow behaves similarly when the Reynolds numbers are close to each other even though the model scales are different in size,which demonstrates that the Reynolds number is a dominant factor characterizing the flow field.The experimental results obtained within the capability of the in-hand shock tunnel show that the agreement with that of the CFD simulation is reasonable. Furthermore,a kind of unexpected“self-starting”configuration was also observed experimentally under very low Reynolds number condition.It is argued,with the help of numerical simulation, that laminar flow is favourable for the occurrence unusual “self-starting”whereas turbulent flow is the opposite,although the mechanism needs to be clarified in the future.

Separation control of an airfoil by splayed-slit-synthetic-j et-actuator

Zhang Dongyu, Gu Yunsong, Cheng Keming, Zheng Faming

2014, (3): 32-38. doi: 10.11729/syltlx20130061

Abstract(167) PDF(6)

Abstract:
A new type of splayed-slit-synthetic-jet-actuator(SSSJA)which is useful for sepa-ration flow control was designed.The core component of the acoustic excitation type actuator was a powerful loudspeaker(4 W).The j et velocity depends on two parameters of excitation frequency and voltage.Particle image velocimetry(PIV)and boundary layer probe was used to study the in-teraction between the jet flow and the main flow.Results revealed that the promotion of both flow dilution and the power of the boundary layer are responsible for the control effect.Flow con-trol on a three-dimensional NACA633-421 airfoil was then conducted to investigate the effect of two parameters of dimensionless energy ratio Cμand the location of the actuator array.Both pres-sure and force measurements data show the ability of SSSJA to reattach the separation flow and to delay the stall at high angles of attack.The control effect gets better along with the larger val-ue of Cμ.At Cμ= 0.00168,maximum of the lift coefficient and the stall angle were increased by 5.92% and 2.5°,respectively.Chordwise location of the actuator array was proved to be a vital parameter in separation flow control.The behavior of the array located at 0.3c is better than the one located at 0.55c.The difference in the control effect is determined by the relative position of the actuator array and the separation point.Experiments were conducted at the wind speed of v∞= 16m/s and the chord-based Reynolds number of Re= 2.7×105 .

Design and experimental study of osculating inward turning cone waverider/inlet (OICWI)

He Xuzhao, Zhou Zheng, Mao Pengfei, Le Jialing

2014, (3): 39-44. doi: 10.11729/syltlx20120176

Abstract(117) PDF(7)

Abstract:
An integration design method of osculating inward turning cone waverider inlet (OICWI)are put forward in the paper.The performance of a typical inlet designed by the method has been validated by numerical simulation and wind tunnel tests.The waverider inlet integration design method of OICWI is conceived based on osculation axisymmetric and stream line tracing theory.The basic flowfield was firstly conducted by Method of Characteristics (MOC)and basic inner compression cone,then the inlet configuration was induced by streamline tracing technique. At the same time,theoretic characteristic of the inlet was calculated by MOC.The accurate per-formance of the OICWI is analyzed using Computational Fluid Dynamics (CFD)software.De-tailed flowfield simulation results were directly compared to experimental data to evaluate the accuracy of the numerical model and provide insight into the experimental flowfield behavior.The experiment study was fulfilled in China Aerodynamics Research and Development Center (CRADC)’sΦ0.5m hypersonic wind tunnel.The numerical/experimental results analyses show that the design method of OICWI is reasonable.The inviscid numerical simulation results agree well with theoretical design results in the design condition.The numerical simulation results show that OICWI has high pressure recovery in design and off-design condition.The flowfield be-havior obtained by CFD indicates that the isolate exit flow field has benign uniformity and OICWI has high flow capture ratio.The experimental results show that the OICWI can start from Mach number 5 to 7 .The flow field structure and pressure distribution agree well with numerical anal-ysis results.

Investigation on effect of syngas components and Reynolds number on premixed turbulent syngas flame structure

Zhou Yajun, Wang Zhihua, He Yong, Weng Wubin, Zhou Zhijun, Zhou Junhu, Cen Kefa

2014, (3): 45-51,77. doi: 10.11729/syltlx20140033

Abstract(99) PDF(6)

Abstract:
The application of simultaneous single-shot imaging of OH radicals using the non-intrusive planar laser-induced fluorescence (PLIF)method to investigate lean premixed turbulent jet flame was reported.13 working conditions were designed according to real component of typi-cal air gasification coal syngas.Effect of H2 content,CO/(CO+CH4 )relative ratio and Reynolds number on flame structure were studied based on the acquired OH-planar laser-induced fluores-cence (OH-PLIF)images.And then,this method was applied to typical premixed turbulent py-rolysis syngas flame.Pyrolysis syngas contained over 80 percent combustible component,which led to a much higher calorific efficiency.Results indicated that,each of H2 content,CO/(CO+CH4 )relative ratio and Reynolds number played an important role in the formation of OH radical during combustion,therefore had an effect on combustion structure.H2 content increase and Reynolds number increase can enhance OH-PLIF signal in measuring range,which means they promote the formation of OH radicals.While the increase of CO/(CO+CH4 )relative ratio have an obviously decrease effect on OH signal.With the increase of Reynolds number from 4000 to 12000,the flame surface became wrinkled,the pulsation intensity of syngas flame became larger, and the unburnt area lengthened due to the increase of total amount of syngas.In general,Reyn-olds number strengthened the combustion progress.When the H2 ratio raised from 0 to 25% by 5% per step,the results showed that both length and width of the unburnt area reduced,and OH-PLIF signal became much stronger at upstream of the flame.In one word,the increase of H2 ratio can accelerate turbulent syngas combustion.As the CO/(CO+CH4 )relative ratio was investigated as a variable,the measurement results became complex.CO/(CO+CH4 )relative ratio was enhanced from 0 to 100% by 20% per step,and a turning point appeared during the procedure.In the first 4 working conditions,in which the CO/(CO+CH4 )relative ratio was 0 to 80%,the unburnt area was slowly reduced both in height and width dimensions.After that, with the CO/(CO+CH4 )relative ratio continue increasing to 100%,the unburnt area suddenly enlarged to a very high scale.Another undeniable fact need to be pointed out was that,OH-PLIF signals in these measurements series continued decreasing along with CO/(CO+CH4 )relative ratio increase.That’s because,CO/(CO+CH4 )relative ratio increase led to the decrease of CH4 ,which was the only one hydrogen supply to form OH radicals.Before the turning point, OH radical density could still satisfy the demand of reaction,so it strengthened combustion pro-gress;after the turning point,combustion was obstructed since the short of OH radicals.This OH-PLIF image analysis system was applied in premixed turbulent pyrolysis syngas flame,and the results showed an agreement with what discussed above.

Passive control of an offset attaching j et using a perforated plate

Gong Sheng, Wu Chuijie, Gao Nan

2014, (3): 52-57. doi: 10.11729/syltlx20130096

Abstract(147) PDF(6)

Abstract:
The effect of porous wall on the dynamic motions of an offset attaching planar j et was studied using experimental methods.The offset jets developed along perforated walls with different open area ratios (OAR)from 0% (solid wall)to approximately 40%.The fluctuating pressure on the bottom wall was measured using an array of microphones embedded in the wall a-long the centerline of the facility.The flow fields were also visualized using the smoke wire tech-nique.It was found that the root-mean-square values of the fluctuating wall pressure decreased when the wall porosity increased,while the average length of the recirculation region increased at the same time.The cross-spectra of the fluctuating wall pressure measured at different down-stream locations showed that the low frequency flapping motion disappeared when the open area ratio was more than 20% of the total area of the wall.The attaching jet behaved like a two-di-mensional free j et when the open area ratio of the wall was more than 40%.The spectra of the wall pressure also showed that the large scale vortices in the inner shear layer of the attaching j et propagated a longer distance in the flow with a larger porosity,which indicated the low-frequency flapping motions in the j ets with small open area ratio hindered the development of higher-fre-quency shear layer vortices.

Investigation on multi-body interference and separation by grid force measurement at supersonic condition

Wang Yuanjing, Qian Fengxue, Chang Lixia, Yi Guoqing, Tao yang

2014, (3): 58-62. doi: 10.11729/syltlx20130003

Abstract(133) PDF(7)

Abstract:
A set of quasi CAV model composed of a external model and a internal model was designed according to foreign public documents,and it was used to study the multi-body interfer-ence during separating by grid force measurement at 0.6m×0.6m transonic/supersonic wind tu-unel.The results show that the aerodynamic characteristcs of the internal model would change dramatically during the separation.While the internal model is leaving the external model along the axis,its aerodynamic characteristcs develops towards the value in free stream.Furthermore, dramatical change of its aerodynamic characteristcs will be induced due to the normal location changing.Two factors induced this dramatic change of the aerodynamic characteristcs.The first comes from the unbalance development of wake flow and the head shock wave during the internal model moving from the wake flow region to free stream flow region,which changes the flow structure of the internal model.And the second comes from the change of local velocity induced by the asymmetric base flow expansion,which induces the more dramatic change of the aerody-namic characteristcs.

A high-resolution algorithm for 2D temperature reconstruction using TDLAS and numerical simulation

Li Jinyi, Zhu Keke, Du Zhenhui, Zhou Tao, Yao Hongbao

2014, (3): 63-71. doi: 10.11729/syltlx20130059

Abstract(236) PDF(11)

Abstract:
We develop a tunable diode laser absorption tomography algorithm for two-dimen-sional (2D)temperature reconstruction based on orthogonal optical paths.In order to evaluate the reconstruction method,we analyzed the 2D reconstruction results of two different tempera-ture phantoms by means of numerical simulation of N×N uniform grid arrangement consisting of 2N (N≥3)light of sight (LOS)measurement path.The maximum deviation and the mean devi-ation were defined to describe the effect of the value of N on the reconstruction results.The re-sults show that for the single symmetrical peak non-uniform temperature phantom,the maxi-mum deviation of the reconstruction temperature is less than 50K(2.5%),the maximum devia-tion fluctuates with N parity and the overall trend is decrease with N increasing.The mean devia-tion is reduced as N increases,which means the reconstruction is better with N increasing.But when N≥9 ,the improvements are not distinct any more.For the bimodal temperature phantom, the maximum deviations of the results using this 2D reconstruction method are more than 350K (15.2%)and the mean deviations are greater than 0.03.What’s worse,there is a serious distor-tion.However,the reconstruction results can be improved by added measurement path diagonal-ly across the tested temperature field.The study is helpful for the real 2D measurement system setup and actual application.

Application of Langmuir probe in high frequency plasma wind tunnel

Pan Dexian, Jiang Gang, Wang Guolin, Ma Haojun, Liu Liping, Luo Jie

2014, (3): 72-77. doi: 10.11729/syltlx20130070

Abstract(180) PDF(17)

Abstract:
In order to study the electromagnetic characteristics of the plasma sheath around hypersonic aircraft in High-Frequency Plasma Wind Tunnel,a new Langmuir probe system has been developed in this paper.High-Frequency Plasma Wind Tunnel is ideal facility for the re-search of electromagnetic characteristics of the plasma sheath,and electron density,electron tem-perature and their distribution is very important to the researching test.In this probe system,the high performance molybdenum probe and adjustable power device have been manufactured.By this probe system,the test principle and data processing method are discussed,the electron densi-ty and its change rule of core area for wind tunnel with different operating power and different gas flux are measured.At the same time,the electron density radial distribution is measured with the same operating power and gas flux.Moreover,the test results have been compared with the mi-crowave means data.It shows that this electrostatic probe system can meet diagnostics of flow field parameters in high frequency plasma wind tunnel well,and can provide reliable data to sup-port the numerical simulation of wind tunnel flow field and electromagnetic characteristics study of plasma sheath.

Investigation and analyse on the diffuser of hypersonic wind tunnel

Tong Hua, Sun Qizhi, Zhang Shaowu

2014, (3): 78-81,103. doi: 10.11729/syltlx20120201

Abstract(151) PDF(19)

Abstract:
Diffuser is the critical part of the hypersonic wind tunnel,The mainly role of the diffuser is to increase the static pressure at the diffuser exit.The wall static pressures and near-wall total pressure pressures along the diffuser are measured,and a measurement rake is installed to measure the flow parameters at the exit of diffuser and evaluate the internal flow performance of the diffuser.The results indicate that the phenomenon of“speed slow-up-slow-up”in inflow of the diffuser appears,the existing diffuser can ensure normal start of the wind tunnel and isolate the test section from disturbance of back pressure;the efficiency of the diffuser is correspond to the similar ones of foreign countries.If the stilling chamber pressure is lower,the diffuser has better effect of reducing speed and boosting pressure;conversely,the effect is not well,the Mach number at the exit is higher.

Experimental research of arc heater with multiple electrodes

Yao Feng, Zhu Chao, Chen Dejiang, Zhou Wei, Huang Zhenjun, He Min

2014, (3): 82-86. doi: 10.11729/syltlx20130048

Abstract(230) PDF(8)

Abstract:
The safely operation with multiple electrodes is important for arc heater running re-liability with large arc current.The influence of ballast resistor settings,gas flow and arc current were observed for arc heaters with a pair of cathodes matching single anode,and with a dual elec-trodes separately.Results show that the ballast resistor settings is the key factor for division of current between electrodes,and the operation parameters such as gas flow and current are insen-sitive with the arc current distribution.For arc heater with a pair of cathodes and single anode, ballast resistors with the certain difference connected simultaneously to inner and outer cathodes is a necessary for division of current between cathodes.For arc heater with a dual electrodes,the division of current between each electrode could be successfully achieved so far as the ballast re-sistors connected to cathodes.And the different current distribution proportions could be a-chieved by adjustment of the ballast resistor.When arc heater operated in multiple electrodes mode,the ballast resistor settings with lowest power loss and uniform division of current should be selected.

Research on vulnerability analysis method for satellite impacted by space debris

Zhou Zhixuan, Huang Jie, Ren Leisheng, Li Yi, Liu Sen

2014, (3): 87-92. doi: 10.11729/syltlx2014pz40

Abstract(224) PDF(7)

Abstract:
For the sake of risk assessments of centimeter/millimeter-level space debris impac-ting satellites,a vulnerability analysis method has been developed to estimate the system failure probability PK/H of satellite with different damage degree.The proposed method is constructed on the basis of Failure Mode and Effect Analysis (FMEA ),combined with Shot-line method and failure tree method.In this paper,the main idea and each key technique of this vulnerability anal-ysis method in detail were introduced and an application example was presented in the end.This method can be applied for manned space missions also,which is significant for risk assessments of aircrafts and shielding structure design optimization.

Test and simulation study on characteristics of pressure container filled with water under hypervelocity impact

Ke Fawei, Zhou Zhixuan, Huang Jie

2014, (3): 93-97. doi: 10.11729/syltlx2014pz17

Abstract(169) PDF(5)

Abstract:
In order to study the characteristic of pressure container impacted by space debris, the characteristics of pressure container filled with water under hypervelocity impact were studied by test and simulation.The targets were ball pressure containers welded by stainless steel and were charged with water occupying about 80% volume of container and nitrogen of 2.0MPa be-fore test.The water was used to simulate liquid in the pressure container of spacecraft,and the nitrogen of 2.0MPa was used to simulate the work pressure of container.The projectiles were a-luminum spheres,and the impact velocities were about 2.5km/s.The damage models of ball pressure container were obtained by test,the moving characteristic of aluminum sphere in water was simulated.The results showed that the main damage were perforation and burst for ball pressure container filled with water under hypervelocity impact.The fragments generated by pro-j ectile impacting pressure container were decelerated evidently by the water in container which caused no evident damage on the back wall of pressure container.Under the same working pres-sure,the pressure container with low designing pressure would burst more possibly.The study conclusions provided reference for designing and protection from space debris of pressure contain-er of on-orbit spacecraft.

Numerical simulation of honeycomb sandwich panel under hypervelocity impact of ice particle

Shan Li, Zheng Shigui, Yan Jun

2014, (3): 98-103. doi: 10.11729/syltlx2014pz18

Abstract(203) PDF(7)

Abstract:
With the orbital debris environment worsening,research on the hypervelocity im-pact phenomena of orbital debris attracts more and more interests of investigators all over the world.The density of some orbital debris is close to ice.Honeycomb sandwich panels are the im-portant component parts of spacecraft structures and protect equipments inside.Therefore,re-search on honeycomb sandwich panel under hypervelocity impact of ice particle is very imperative and necessary.In this study,we used numerical simulation method to study honeycomb sand-wich panels which are impacted by ice particles and evaluated their performance of resisting the hypervelocity impact of ice particles.The results show that ice particles can penetrate honeycomb sandwich panels.The ice particle of 1mm in diameter penetrated the honeycomb sandwich panel at the velocity of 12km/s;the ice particle of 2mm in diameter penetrated the honeycomb sand-wich panel at the velocity of 11km/s or 12km/s;the ice particle of 3mm in diameter penetrated the honeycomb sandwich panel at the velocity of 5km/s and above;the ice particle of 4mm or 5mm in diameter penetrated the honeycomb sandwich panel at the velocity of 3km/s and above. When the honeycomb sandwich panels are penetrated,a lot of debris dash out through the hole of the rare panel and will destroy equipments inside the spacecraft.Additionally,when the kinetic energy of ice particles are close,the diameters of the ice particles will affect the simulation results.

Research on the driving characteristics of high speed flyer using KrF laser

Li Yejun, Wang Zhao, Tian Baoxian, Liang Jin, Han Maolan, Lu Ze, Tang Xiuzhang

2014, (3): 104-109. doi: 10.11729/syltlx2014pz26

Abstract(194) PDF(3)

Abstract:
KrF excimer laser (248nm)has high spatial uniformity by using induced spatial in-coherence technology.After image relay and amplification by optical angular multiplexing tech-nology,non-uniformity of image surface of focal spot is 1 .6%.The spot spatial uniformity decreases with increasing distance of deviating image surface,the spatial non-uniformity is up to 5% at 3mm place deviating image surface.Laser directly drives planar target with ablation layer, the effects of laser spatial uniformity on flyer planarity and integrity were investigated.The results show when the non-uniformity of laser is below 2%,the integrity of inference fringes measured by laser velocity interferometer system for reflector keeps very well,the inference frin-ges last about 20ns after fringes jump.And the flyer can fly about 150 microns.The roughness of discontinuity is 62ps,which indicates that the shock wave planarity is good.The target debris deposited on sputtering film from the target of about 120mm is larger particles,which confirms the flyer has better integrity.When the laser non-uniformity is 5%,the interference fringes dis-appear completely after fringes jump,and the target debris deposited on sputtering film becomes powder,which indicates the shock wave planarity is very poor under this laser condition.The experimental results show hydrodynamic instability seed is weak at good condition of the uni-formity of laser,the development of shock waves is not strong enough to make the flyer disinte-gration when shock waves transfer from the front surface to rear of larget.When the laser non-uniformity is about 5%,hydrodynamic instability seed driven by laser is very strong.When the shock wave transferred to the target back,hydrodynamic instability develops strong enough to make the flyer disintegration even gasification,which leads to the disappearance of interference fringes.So shock planarity driven by laser is strongly dependent on the laser beam spatial uni-formity,and the planarity and integrity of flyers depend on the shock planarity.According to the simulation results using one dimensional HYADES program,the ablation layer thickness should be reduced in order to improve the velocity of flyer.At the condition of thinner ablation layer,la-ser and ablation parameters do not match,shock waves driven by laser can accelerate the flyer multi-times.KrF laser with power density of about 1012 W/cm2 drove flat target of 5μm aluminum with 50μm Kapton ablation.Flyer trajectory was obtained using side-on shadowgraph.The curves of flyer velocity and acceleration were obtained by fitting the trajectory curve.Acceleration reaches 0.23×109km/s2,the velocity of flyer is about 9.8km/s.And the HYADES simulation shows there are 4 acceleration processes,the flyer velocity is about 10km/s.The results of experiment and simulation agreed very well.At the same conditions,simulations also show when the abla-tion thickness decreases to 30μm,the flyer velocity can be up to 16.5km/s.Target debris from backward jet maybe pollutes the laser focusing system components for too thin ablation.These all need to be verified by experiments.

Experimental study on dynamic response of bulk metallic glass under high velocity impact

Li Tao, Tan Duowang, Li Qiang, Tan Xingchun, Fu Hua

2014, (3): 110-113. doi: 10.11729/syltlx2014pz25

Abstract(182) PDF(3)

Abstract:
As a novel material with high strength,bulk metallic glass received concern of many researchers all over the world.For potential military applications,it was important to un-derstand the dynamic response of this material under high strain rate.To this end,Electric Gun was chosen to study dynamic response of a newly prepared Zr-based bulk metallic glass.In the E-lectric Gun experiments,the velocity of electric explosion driven plastic flyer in 0.5 mm thick-ness could reach 3 .5 km/s.Based on bulk metallic glass sample/window interface particle veloci-ty profiles measured by high resolution DPS laser interferometer,two important dynamic behav-iors were obtained under high strain rate about 106/s.In a shock pressure range of 15~25GPa, the Hugoniot elastic limit was determined to be about 2 .4GPa,and the shock wave velocity (Ds) vs.particle velocity (up)Hugoniot data were linearly fitted by Ds= (4.4±0.1)+(0.58±0.08)up.

2014 Vol. 28, No. 3