2009 Vol. 24, No. 6

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Convective heat transfer characteristics of impingement cooling for a self-excited precessing jet
ZHOU Jing-wei, GENG Li-ping, WANG Yu-gang
2009, 24(6): 1197-1203.
Abstract PDF(1007KB) icon1655 icon431
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Heat transfer performance under precessing jet impingement cooling was experimentally studied.The flow characteristic of the self-excited precessing jet was firstly investigated by a frequency spectra analysis to the jet velocity obtained at the nozzle exit.It was demonstrated that the precessing frequency of the jet was greatly influenced by the nozzle diameter while the Strouhal number was only slightly influenced by the nozzle diameter and the flow rate.The heat transfer experiments indicate that,because of the considerable decrease of the bulk velocity in a precessing jet caused by the surrounding air entrainment,the convective heat transfer coefficients of a precessing jet impingement decrease as compared to that of the corresponding inline jet.The influence of the nozzle diameter on heat transfer characteristics,however,has no uniform trend for three sized nozzles.It is shown that,only in the case that a precessing jet flows parallelly over a heating plate,the convective heat transfer coefficient is higher than that of an inline jet.
Conjugate flow and heat transfer investigation of a turbine cascade
ZENG Jun, QING Xiong-jie
2009, 24(6): 1204-1210.
Abstract PDF(2424KB) icon1709 icon517
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A numerical method with three-dimensional Reynolds averaged Navier-Stokes equations and the two-equation turbulence model shear stress transport(SST) model including the transition model was used to investigate the conjugate heat transfer problems of a turbine cascade called MARKⅡ,which was cooled with internal convection method.Under the conditions of various inlet turbulence intensities,the conjugate calculations were executed and the results were compared with the experimental data.The results show that the numerical method with the transition model has higher accuracy to predict the cascade surface temperature and external heat transfer coefficient(EHTC) distributions.The inlet turbulence intensity especially low inlet turbulence intensity has great effects on cascade surface temperature and heat transfer distributions,but has little effect on cascade surface pressure distributions.
Numerical simulation on infrared radiation suppressant of hot exhaust with the spherical particles
ZHANG Jing-yu, CHANG Hai-ping, WANG Hui-yuan
2009, 24(6): 1211-1218.
Abstract PDF(1617KB) icon1542 icon402
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Based on aerosol infrared radiation(IR) stealth technique,the characteristics of IR suppressant(3～5μm) on hot exhausts with spherical particles has been numerically investigated.The extinction characteristic parameters including extinction efficiency factor and asymmetry factor were calculated based on Mie scattering theory,which is decided by diameter parameter and complex index of refraction.The flow field was achieved by Fluent software,and IR radiation intensity of the target was calculated by ray-tracing-method.The parameters investigated include diameter parameter,complex index of refraction,concentration of the particles,injection velocity of the particles and coefficient of heat conduction of the particles.The results show that IR suppressant affected by the diameter parameter of discrete particles is the most prominent.And the best IR suppressant exists when the diameter of particles is in the range of 1.0μm.
Study on the abnormity of the axial-symmetric boundary in simulation of shock-induced combustion
LIU Chen, WANG Jiang-feng, WU Yi-zhao
2009, 24(6): 1219-1228.
Abstract PDF(2356KB) icon1442 icon419
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The abnormity of the axial-symmetric boundary in simulation of shock-induced combustion was discussed.Practice has shown that the abnormity(distortion of combustion front) may appear near the axis when the velocity was below the detonative speed.Four key factors,such as the solution method of the boundary,numerical scheme,chemical reaction model and mesh were analyzed.It is shown that all factors can cause the abnormity,but the numerical scheme should be the most fundamental one.The abnormity may be similar to the‘carbuncle' problem.Some reasonable measures are proposed,and numerical results show the availability of these proposals.
Numerical study on adiabatic wall cooling effectiveness and convective heat transfer coefficient of effusion cooling
XIE Hao, ZHANG Jing-zhou
2009, 24(6): 1229-1235.
Abstract PDF(1715KB) icon1673 icon422
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The influences of the adjacent holes spacing and blowing ratio on the adiabatic wall cooling effectiveness and convective heat transfer coefficient of effusion cooling with the film holes in staggered arrangement were numerically investigated.The results show that,with the decrease of adjacent holes spacing or the increase of blowing ratio,the average temperature in the film holes region reduces and the temperature distribution uniformity is improved for all the calculated cases,so that the adiabatic wall cooling effectiveness increases along with the convective heat transfer coefficient.In relation to the decrease of adiabatic holes spacing,the influence of blowing ratio increase is not obvious,especially when the blowing ratio is greater than 1,the influence becomes very weaker.
Experimental study on detonation characteristic of propane
ZHANG Peng-gang, HE Xiao-min, LI Jian-zhong, ZHANG Jing-zhou
2009, 24(6): 1236-1241.
Abstract PDF(1094KB) icon1699 icon524
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In order to understand the detonation characteristic of propane,a series of single detonation experiments was conducted with air,oxygen and air/oxygen as oxidizer in square detonation tube.Firstly the detonation performance of propane was studied.Secondly the characteristic of deflagration to detonation transition(DDT),spread rule of wave and flame were achieved under the condition of different equivalence ratio and degrees of nitrogen dilution.The ion-probes and pressure transducers were utilized to get the velocity and pressure in the tube,respectively.The results indicate:(1)C3H8/air mixtures could not form detonation wave,and that the DDT distance of C3H8/O2 mixtures was very short,(2)the run-up distance was minimum for stoichiometric mixture,increasing as the nitrogen dilution became richer,and(3)shock and flame have similar change trend in DDT.
Numerical simulation of ignition in detonation tube with/without obstacles by CE/SE
SUN Kong-qian, FAN Wei-jun, YANG Mao-lin
2009, 24(6): 1242-1247.
Abstract PDF(1432KB) icon1593 icon444
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A space-time conservation element and solution element method(CE/SE) was used to simulate the formation and propagation process of two-dimensional detonation with/without obstacles.The detonation mechanisms were analyzed.Influential factors to deflagration to detonation transition(DDT)were evaluated,including the ignition temperature,the tube diameter and the obstacles.Model equation was non-dimensionalized,and the implicit trapezoidal technique was established to handle stiff source term.Results show that the ignition energy is related to the ignition pressure.The higher ignition temperature,the smaller tube diameter or setting obstacles could accelerate DDT process under the condition of small ignition energy.The results offer a reference to study detonation ignition and DDT process.
Effect of swept structure on ramp injectors in supersonic combustion
WU Hai-yan, ZHOU Jin, SHAO Yan, ZHANG Shun-ping
2009, 24(6): 1248-1252.
Abstract PDF(1220KB) icon1738 icon425
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To improve the efficiency of supersonic combustion and reduce combustor length,two structures of ramp injectors were designed to increase the mixture of fuel and air in supersonic flow.The experiments of schlieren,oil flow and flame transfer were conducted for the ramps.By combining the experiment results and the numerical simulation,we analyzed the influence of swept angle in the supersonic mixing course,and found that the swept ramp could facilitate the formation of stream eddies and accelerate the lifting of fuel jet flow,which would not only enhance the mixture but also stabilize the flame.
New simulation approach to the unsteady fluid network and the application
HOU Sheng-ping, TAO Zhi, HAN Shu-jun, DING Shui-ting, XU Guo-qiang, WU Hong-wei
2009, 24(6): 1253-1257.
Abstract PDF(605KB) icon1558 icon422
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A new approach combining fluid network and unsteady simulation method was developed to predict the unsteady characteristic of pressure,temperature and mass flow rate of the flow in engine.The fluid system was simplified into fluid network comprised of nodes and branches.Conservation equations were solved by a newly introduced method combining pressure-correctional method and differential method.The program was applied to propulsion test article(PTA) model,which was compared with the empirical correlation and numerically simulated result of general fluid system simulation program(GFSSP) of NASA.The computational results show good agreement with the benchmark.Then the program was applied to the simulation of the jet engine cooling system.
Injection characteristics of the supercritical jet fuel injected into the atmospheric environment
LIANG Huo-sheng, GAO Wei, XU Quan-hong, XU Guo-qiang, LIN Yu-zhen
2009, 24(6): 1258-1263.
Abstract PDF(682KB) icon2145 icon445
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The injection characteristics of supercritical RP-3 aviation kerosene injected into a quiescent atmospheric environment were studied using schlieren system.The jet generated a barrel shaped wave,Mach disk and reflected shock wave in the downstream of the nozzle exit,with the structure of the jet similar to highly underexpanded air jet.The test results indicate that the axial location of the Mach disk increases with the increasing reduced pressure,however,the reduced temperature almost has little effect on the location of the Mach disk.The mach disk diameter increases with the increasing reduced pressure but decreases with the increasing reduced temperature.The jet length increases with the increasing reduced pressure but decreases with the increasing reduced temperature.
Experimental research on heat transfer characteristics of denser jet array impingement
WANG Lei, ZHANG Jing-zhou, YANG Wei-Hua
2009, 24(6): 1264-1269.
Abstract PDF(1300KB) icon1770 icon468
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Several jet array impingement experimental models with different holes spacing were designed to investigate the effects of impinging jet Reynolds number and geometry parameters on the local heat transfer enhancement by using the transient Infrared thermography method.The results show that:(1)the heat transfer coefficient increases with the increasing of impinging jet Reynolds number,(2)the heat transfer enhancement becomes weaken when the jet holes spacing or jet impinging distance increase,and(3) in the case of jet holes spacing ratio arranged from 3 to 5,the heat transfer enhancement for inline jet array is higher than that of staggered jet array,but in the case of jet holes spacing ratio is 2,the heat transfer enhancement for the inline jet array is higher in the front jet rows but lower in the rear jet rows compared with staggered jet array.
Experimental investigation on discharge coefficient of jet impingement holes within semi-confined channel
ZHANG Ze-yuan, ZHANG Jing-zhou, YANG Wei-hua
2009, 24(6): 1270-1274.
Abstract PDF(930KB) icon1485 icon467
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An experimental investigation for determining the discharge coefficient of jet impingement holes within semi-enclosed channel was performed.According to the jet impingement configurations with single row or double row holes,the effects of the holes arrangement and flow parameter on the discharge coefficient were considered,such as: the span holes pitch-to-diameter ratio,the streamwise holes pitch-to-diameter ratio,the impingement distance-to-diameter ratio,the jet oblique angle and the jet Reynolds number.Comparatively,the above factors on the discharge coefficient were discussed.
Experimental study on the vortex tubes with different Mach number nozzles
JIA Hong-shu, WU Yu-ting, MA Chong-fang, GE Man-chu
2009, 24(6): 1275-1278.
Abstract PDF(613KB) icon1596 icon418
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In order to find out the vortex tube configuration with the best cooling temperature difference,nozzles with different Mach numbers were designed and manufactured,the experimental system was set up and the performances of these nozzles were measured.The result shows that the vortex tube has better energy separation effect with outlet Mach number between 0.5 and 0.8.But when the Mach number is up to 0.9,the effect would be worse.The refrigeration performance of the vortex tube with the outlet Mach number of 0.8 is best from 0.4 to 0.6MPa in inlet pressure,but the performance difference varied little with input pressure over 0.6MPa.
Reliability analysis method of fretting fatigue life
CUI Hai-tao, WANG Zhen, WEN Wei-dong, XU Ying
2009, 24(6): 1279-1283.
Abstract PDF(492KB) icon1878 icon446
Abstract:
A fretting fatigue reliability analysis method was developed.The contact area was in a multi-axial stress state under fretting conditions.The multi-axial fatigue parameter based on the critical plane was used to predict the fretting fatigue life.On the basis of calculating determinate life,the randomicity of modulus of elasticity,friction coefficient and material constant in the life model were considered,and the fretting fatigue life reliability model was obtained by Monte-Carlo simulation method along with the response surface method.Finally,the method was applied to analyze fretting fatigue life reliability of dovetail joint,proving the feasibility and validity of this method.
Dynamic response analysis of dual rotor-ball bearing-stator coupling system for aero-engine
ZHOU Hai-lun, CHEN Guo
2009, 24(6): 1284-1291.
Abstract PDF(1812KB) icon1798 icon459
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The aero-engine with dual rotor was researched as an object,and a dual rotor-ball bearing-stator coupling dynamic model was established.In the model,the coupling effect of inter-rotor bearing between the low pressure rotor and high pressure rotor,or between the outer race of ball bearing and bearing housing,and between the flexible support and squeeze film damper,or the rub-impact between high pressure rotor and stator were considered.In the model of ball bearings,the clearance of bearing,the nonlinear Hertzian contract force between balls and races and the varying compliance vibration were considered.Then the numerical integral method was used to obtain the system's responses.Finally,the dynamic response analysis and verification of dual rotor-ball bearing-stator coupling system for aero-engine were carried out.
Finite element analysis and application of friction damper tangential contact stiffness
SHI Ya-jie, ZHU Zi-gen
2009, 24(6): 1292-1298.
Abstract PDF(1476KB) icon1957 icon470
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A convenient method was developed to estimate the tangential contact stiffness between dry friction dampers using the general finite element method(FEM) software.The influences of various parameters such as normal preload,friction coefficient,damper material properties and the radius of the cylinder damper etc on the contact stiffness were investigated in detail.The results show that,the contact stiffness improves with increase in these parameters.A formula of calculating the tangential contact stiffness for variable normal preload was obtained by fitting the results,making it more conveniently to take into account the variety of contact stiffness in calculating the nonlinear response of shrouded blade instantaneously.Eventually,influences of the contact stiffness on the shrouded blade nonlinear response were studied with the formula,the results indicate that,the resonant frequency of the blade increase and the peak amplitude decrease gradually with increase in the contact stiffness,and all of which are close to a fixed value respectively.
Boundary element analysis of damage tolerance of powder metallurgy turbine disk
WEI Da-sheng, WANG Yan-rong, LU Li-peng
2009, 24(6): 1299-1304.
Abstract PDF(879KB) icon1446 icon409
Abstract:
An analysis model of crack growth was established by means of boundary element method(BEM),which was used to simulate the crack growth behavior of a powder metallurgy(PM) superalloy,FGH95.The calculation results show that,the predicted life of crack propagation is in good agreement with the experimental data,and the model is veracious and feasible.Then the model was developed to analyze the damage tolerance characteristic of PM turbine disk containing defects,and the predicted crack propagation life was also given.It indicates that the BEM could be used to estimate the crack growth characteristic of complicated component effectively in engineering analyses,and also give a more reasonable value as compared with conventional life prediction method.
Effects of rolling-ball diameter of ceramic bearing on rotor critical speeds
CHEN Wei, DU Fa-rong, LI Yun-qing
2009, 24(6): 1305-1310.
Abstract PDF(1940KB) icon1567 icon530
Abstract:
Based on Hertz contact theory,the influence of rolling-ball diameter of ceramic bearing on bearing stiffness was analyzed.By these laws,it's possible to tune rotor critical speed in design of micro turbine jet engine and verify it experimentally.Two groups of hybrid ceramic bearings were taken as rotor supports to measure the critical speed.It is proved that we can change rotor critical speed effectively by this method.And it also provides experience for changing critical speed in micro turbine jet engine design.
Modification of Z-A model and the prediction of the constitutive model
ZHANG Hong-jian, WEN Wei-dong, CUI Hai-tao, XU Ying
2009, 24(6): 1311-1315.
Abstract PDF(461KB) icon1719 icon470
Abstract:
Zerilli-Armstrong(Z-A) model was developed based on the constitutive model of thermally activated dislocation kinetics.But,some simplifying assumptions in Z-A model decreased its predicted accuracy.In order to improve the predicted accuracy,the strain hardening exponent function that considers the coupled effect of the strain rate and the temperature was introduced into Z-A model.And the modified Z-A model was used to describe flow behaviors of alloy IC10 under different experiment conditions.As compared with the predicted data of classical Z-A model and the experimental data,it was found that the predicted accuracy of the modified Z-A model was improved obviously.The max average relative error decreased from 6.41% to 3.65%.
Research on reliability of turbo-rotor with random structure
WANG Xin-gang, ZHANG Yi-min, WANG Bao-yan
2009, 24(6): 1316-1320.
Abstract PDF(320KB) icon1643 icon423
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Based on the traditional stress-strength interference model,and with consideration of the randomness of structural size of turbo-rotor,temperature stress,rotating speed,external loads and material strength,the reliability of the location with largest local stress for rotor was studied using integral stochastic finite element method and Gram-Charlier series method.The relative error between the result of this paper and the one of Monte-Carlo is very small,and the result is exact.To avoid a large quantity computation and slow calculation of the finite element method,while the random structural reliability of rotor was computed.
Bayesian networks application to reliability analysis of momentum wheel's ground test
LI Hai-tao, JIN Guang, ZHOU Jing-lun, ZHOU Zhong-bao
2009, 24(6): 1321-1325.
Abstract PDF(1807KB) icon1572 icon436
Abstract:
A lot of intricate information in momentum wheel's ground test has been accumulated.However,an effective method for reliability analysis by fusing such information can hardly be found.The paper firstly proposed a method to build the reliability model of momentum wheel by fusing various test information and expert knowledge using Bayesian network.Then,the reliability assessment,fault diagnosis and sensitivity analysis towards momentum wheel's ground test were carried out using the inference of Bayesian network.The proposed method could solve the problem of reliability analysis and assessment of momentum wheel's ground test,providing a theoretic guidance for reliability test of momentum wheel.
Study of circulation control airfoil with blowing jet using Gao-Yong turbulence model
LI Zhi-qiang, DU Man-li
2009, 24(6): 1326-1331.
Abstract PDF(1549KB) icon1619 icon456
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Gao-Yong turbulence model was applied to simulate the influence of blowing jet on the flow separation control of the airfoil surface.The results show that Gao-Yong turbulence model can not only successfully simulate the location of separation and the aerodynamic force coefficients,but also effectively simulate the blowing effect of flow separation control.Other than increasing lift by inhibiting flow separation vortex on the airfoil surface,the blowing jet can also induce much higher lift through the "package effect" for external flow,especially at the condition of large angle of attack.With the increase of blowing jet momentum coefficient,the lift coefficient of the airfoil increases under the same angle of attack.In addition,the angle of the blowing jet has important influence on "package effect".And the positive angle of the blowing jet is more favorable to the lift coefficients than zero and negative angle.
Simulation study of an aero-piston engine with single stage turbocharger
LIN Hai-ying, LONG Xiang-yang
2009, 24(6): 1332-1338.
Abstract PDF(1936KB) icon1778 icon459
Abstract:
The method was introduced for setting up simulation model of an aero-piston engine.The simulation model of an engine with single-stage turbocharger was set up,and the ground performance's simulation computation was finished.The simulation results were coincident with the test data.On the basis of the former works,the high altitude performance simulation was conducted,and the results were consistent with the fly test data.
Modeling and experimental analysis of UAV electric propulsion system
CHEN Jun, YANG Shu-xing, MO Li
2009, 24(6): 1339-1344.
Abstract PDF(2649KB) icon1912 icon544
Abstract:
A new method for analyzing twin-blade fixed-pitch propeller was proposed based on the theory of corrected blade foil and aerodynamic formula of 3-D wing.According to the characteristics of the brushless motor,the mathematic modeling of the electric propulsion system of unmanned aerial vehicle(UAV) has been set up.More than 17 sets of experimental data of various propulsion systems at zero forward speed were analyzed to verify correctness and relative precision,proving that it could ameliorate the primary parameter designing of UAV.
Three-dimensional numerical simulation of supercooled droplets impinging on a wing
ZHANG Qiang, HU Li, CAO Yi-hua
2009, 24(6): 1345-1350.
Abstract PDF(1735KB) icon1852 icon467
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Based on two-phase flow theory,an Eulerian method was presented to numerically simulate supercooled droplets impinging on a wing.The governing equations for droplets in three-dimensional application were established according to the droplet pseudo-fluid model.A permeable wall was proposed to simulate the droplets' impingement on the wing.The local collection efficiency and impingement area were obtained from the solution of the droplets' flowfield.The computational results of an ONERA M6 wing indicate that,the simulation method presented is feasible and effective,laying a foundation for numerical simulation about ice accretions in three-dimensional application.
Numerical simulation of integrated hypersonic vehicle's aerodynamic performance
HUANG Wei, WANG Zhen-guo
2009, 24(6): 1351-1356.
Abstract PDF(1045KB) icon1567 icon456
Abstract:
Two-dimension coupled implicit Naviers-Stokes equations and standard k-ε viscid models were introduced to simulate the lift characteristic,drag characteristic,pitching moment characteristic and lift-to-drag ratio characteristic of integrated hypersonic vehicle with Hark head configuration working under the conditions of inlet closed,inlet open but unfired and inlet open and fired.The influence of head slenderness ratio on the aerodynamic performance was discussed.It is concluded that the improvement degree of aerodynamic performance designed with the first method is greater than that designed with the second one,meanwhile,with the increasing of head slenderness ratio,the aerodynamic performance of integrated hypersonic vehicle becomes better in evidence,it can satisfy the aerodynamic requirement of cruising vehicles.
Unique design method of subsonic inlet with complex cross-sectional shape
ZHOU Hui-chen, TAN Hui-jun, LI Xiang-ping
2009, 24(6): 1357-1363.
Abstract PDF(983KB) icon1919 icon429
Abstract:
A cross-sectional shape generating method for subsonic inlet design was proposed according to curvature regulation.This unique method can realize the transition of an arbitrary entrance shape to the exit circular shape easily and smoothly.Utilizing this method,an inlet design procedure was programmed,which could accomplish the surface composition of subsonic inlet with complex cross-sectional shape and complex bending style quickly and graphically.As a preliminary application,several diffusers with different entrance shape were generated and especially the design procedure of a slot-shaped inlet like that of X-47 vehicle was described in detail.
Effects of air injection on outlet flow field of compressor cascade
FENG Dong-min, CHEN Fu, CHEN Huan-long, FU Li-peng, WANG Zhong-qi
2009, 24(6): 1364-1371.
Abstract PDF(2492KB) icon1459 icon418
Abstract:
Experiments of a large turning angle linear compressor cascade with air injection slot were carried out,and detailed outlet flow field characteristics at design incidence were described in this paper.The results show that air injection through slots decreases the turning and diffusion of compressor cascade,the aerodynamic performance of the cascade also decreases;air injection energizes the low energy fluid near wake,increases the velocity of the wake,thus the size of the wake region reduces significantly,pitch-wise distribution of flow outlet angle becomes more uniform,slot position has great effect on wake especially with slot located near mid-span;multi-slot configurations have greater effect on outlet flow field than one-slot configurations.
Numerical analysis of two circumferential groove casing treatments about a centrifugal compressor
WANG Qing-wei, LIU Bo, XUAN Yang, BAI Xiao-hui, CHEN Yun-yong
2009, 24(6): 1372-1378.
Abstract PDF(1533KB) icon1752 icon450
Abstract:
In order to extend the stall margin of a centrifugal compressor with splitter blade,two different circumferential groove casing treatments were designed in this paper.The flow fields in compressor with smooth wall and with treated casing were numerically simulated.The results show that the first circumferential groove treated casing extends the stall margin of the centrifugal compressor by 10%,and it also has little influence on pressure ratio and efficiency.The main reason of extended stall margin was that about 75% axial chord of the tip flow field has been improved.The second scheme did not extend the stall margin,because the position of circumferential groove was not accurate,and the groove was too deep.
Research on flow instability triggering process at stall condition of transonic compressor rotor at low Reynolds number
ZHOU Min, WANG Ru-gen, BAI Yun, WANG Xue-de, WU Wei
2009, 24(6): 1379-1384.
Abstract PDF(1108KB) icon2067 icon495
Abstract:
The flow instability triggering process at stall condition of NASA Rotor 37 tr-ansonic compressor rotor at low Reynolds number was investigated by unsteady numerical simulation.The result shows that the effect range of boundary layer radial vortex is extended,the boundary layer separation blockage zone due to radial vortex is assembled at the blade tip,as the stall condition develops,the boundary layer separation blockage zone moves to the blade leading edge,and combines with blockage zone due to shock and tip leakage flow.So the blade tip passage is fully blocked,and compressor flow instability is triggered off.
Experimental investigation about the circumferential treating angle of non-axisymmetric casing treatments
LIU Jian-yong, YUAN Wei, LU Ya-jun
2009, 24(6): 1385-1388.
Abstract PDF(878KB) icon1469 icon436
Abstract:
In order to solve the problem that traditional casing treatment increases the stall margin while reducing the efficiency of compressor,five innovative non-axisymmetric casing treatments with different circumferential treating angles were designed in this paper.In a series of experiments,the stall margin of a compressor increased with the rise of circumferential treating angle,while the isentropic efficiency rose up firstly and fell down later.It was interesting that the stall margin and efficiency of the compressor were both enhanced when the circumferential treating angle of the non-axisymmetric casing treatment was 120°,the reason of which was simply attributable to the fact that non-axisymmetric configuration changed the unsteady tip flow in the compressor.
Numerical simulation of electron backstreaming in ion thruster optics system
ZHONG Ling-wei, LIU Yu, GU Zuo, LI Juan, JIANG Hao-cheng, WANG Hai-xing, TANG Hai-bin
2009, 24(6): 1389-1395.
Abstract PDF(1955KB) icon1682 icon436
Abstract:
Based on particle-in-cell method,a two-dimensional numerical model has been developed to investigate the ion beam extraction phenomena through the optics system of ion thruster.According to the calculation results,the distribution of electric potential between screen grid and accelerator grid,the ion and electron spatial distribution were obtained for various accelerator voltages and accelerator grid radii.The simulation results show good agreement with the experimental data.The results indicate that the accelerator voltage and the accelerator radius have great influences on electron backstreaming.Electron backstreaming happens when the absolute value of accelerator voltage is more negative.The electrons move downstream with the decrease of accelerator voltage.Moreover,electron backstreaming occurs with the enlargement of accelerator radius.Under moderate accelerator voltage and accelerator radius,the electron backstreaming will not happen,and the ion thruster will reach its better performance.
Numerical simulation of gas-gas injector based on orthogonal design
DU Zheng-gang, GAO Yu-shan, JIN Ping, CAI Guo-biao
2009, 24(6): 1396-1401.
Abstract PDF(565KB) icon1608 icon395
Abstract:
The numerical simulation was performed on gaseous oxygen/gaseous hydrogen shear coaxial injector as orthogonal array was applied to guide injector design.The injector combustion location was selected as the indicator of injector performance.The effect of injector mass flowrate,oxygen pressure drop,the hydrogen to oxygen velocity ratio as well as the angle of oxygen post tip on the combustion length were investigated.The range analysis and variance analysis on the results of numerical simulation indicate that the increase of injector mass flowrate make the combustion location far away from the injector faceplate,injector mass flow plays a predominated role in combustion location;and a higher velocity ratio of hydrogen to oxygen shortens the distance between the combustion location and the injector faceplate;the oxygen element drop and the angle of oxygen post tip have minimum impact on combustion location.
Experimental investigation on flow rate and mixing characteristics of splash platelet injector element
LEI Fan-pei, ZHANG Zhen-peng, YAO Ming-ming, FU Li-li, ZHOU Jun
2009, 24(6): 1402-1406.
Abstract PDF(639KB) icon1935 icon463
Abstract:
The flow rate and mixing characteristics of splash platelet injector element with a typical triangular lumen were experimentally investigated by using a collecting device with an area of 16cm×16cm.The effect of main configuration parameters,such as expending angle and relative thickness,on flow coefficient and mixing efficiency factor were obtained.The results show that,flow coefficient and mixing efficiency factor increase firstly and then decrease with the increase of expending angle.Both of them could reach their maximum value of 0.773 and 82.6% when expending angle is at the range of 60° to 75°.It is also found that the relative thickness has great influence on the flow coefficient and mixing efficiency.
Numerical computation of solid rocket motor insulation layer temperature by finite element method
ZHANG Tao, SUN Bing
2009, 24(6): 1407-1412.
Abstract PDF(1656KB) icon1765 icon491
Abstract:
The two-dimensional temperature of insulation layer of solid rocket motor with moving boundary condition was computed.Charred layer-pyrolysis surface-original material model was applied and temperature computation formulas were calculated by taking convection heat transfer between pyrolysis gas and charred layer as heat source.The complicated boundary conditions were transformed into equivalent convection heat transfer and equivalent heat flux.Triangle grid was produced by transfinite interpolation to quicken grid generation and improve the quality of grid.The calculation results show that the astringency and stability of finite element method is good in calculating the temperature of insulation layer of solid rocket motor.
Research of aero-engine two degrees-of-freedom robust controller based on linear matrix inequality approach
WANG Hai-quan, GUO Ying-qing, LU Jun, LI Guang-yao
2009, 24(6): 1413-1419.
Abstract PDF(736KB) icon1527 icon414
Abstract:
In order to overcome the shortcoming of traditional one degree-of-freedom structure and improve the tracking performance while maintaining stability robustness,two degrees-of-freedom control structure was introduced in this paper,then the synthesis techniques based on linear matrix inequality(LMI) was introduced to solve the disadvantages of this controller as compared with the traditional Riccati approach.The two degrees-of-freedom H∞ loop-shaping approach was applied to a turbofan aero-engine,and the hardware in-the-loop simulation based on the real-time simulation platform was implemented.The simulation results show that the excellent robustness and command-tracking properties of the controller are obtained,and the two-degree-of-freedom H∞ loop-shaping methodology is suitable for aero-engine control.
Aeroengine thrust estimation using least squares support vector regression machine
ZHAO Yong-ping, SUN Jian-guo
2009, 24(6): 1420-1425.
Abstract PDF(643KB) icon1812 icon446
Abstract:
The first problem for direct thrust control is thrust estimation.A wrapper algorithm,which reduces the computational complexity and also enhances the model generalization performance,was proposed based on least squares support vector regression machine.In addition,as a surrogate of traditional covariance method,QR decomposition was utilized to build sparse model strengthening the numerical stability.Finally,a thrust estimator design was applied to validate the effectiveness and feasibility of the proposed feature selection algorithm and sparse model using QR decomposition.
Identification of multiple faults of the aircraft engine digital control system
LIU Chun-juan, SONG Hua, QIU Hong-zhuan, ZHU Xin-yu
2009, 24(6): 1426-1431.
Abstract PDF(1747KB) icon1469 icon406
Abstract:
A method for multiple faults identification of aircraft engine digital control system based on fuzzy logic was presented.First of all,a nonlinear model of the digital control system of some turbo-jet engine was built up with introduction of Takagi-Sugeno(T-S) fuzzy model,and then full-decoupling parity equation was applied to detect and isolate the multiple faults,in combination with Kalman filter in identifying the fault parameters of sensors and actuators.The simulation results show that this method can effectively detect and isolate the multiple faults.Also,it can precisely identify the parameters of the faults.
Modification optimization of double helical gears
WANG Cheng, FANG Zong-de, JIA Hai-tao, ZHANG Jun-hui
2009, 24(6): 1432-1436.
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Abstract:
Based on the characteristic of tooth profile modification,the method of three segment modification for pinion profile was presented.Through changing the shape of cutter-edge,three-segment parabola was used to substitute for the linear profile,and cutter surface equation was deduced.Coordinate system for double helical gears meshing was built,and furthermore,tooth contact analysis and loaded contact analysis was proposed.By taking least transmission error as optimization goal and the optimization parameters were obtained by applying complex method.A case study shows that,in the case of axes error,the optimization results of profile and axial modification without consideration of axes error can still obviously reduce the loaded transmission error compared with no modification optimization.Finally,the calculation method of pinion profile modification was given.

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