2011 Vol. 26, No. 5

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Display Method:
Computation and analysis of DSMC and Navier-Stokes model in reentry flight
WANG Bao-guo, HUANG Wei-guang, QIAN Geng, LI Xiang, LI Xue-dong
2011, 26(5): 961-976.
Abstract PDF(1657KB) icon1946 icon26
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The concept of “low Knudsen number characteristic region”,which is ,in the process of reentry,has been presented for the first time,and the fluid in the region has been studied using direct simulation Monte Carlo (DSMC)and Navier-Stokes model respectively.It has been shown by the numerical computation that both of the DSMC code and weak conservative Navier-Stokes code with multi-species,thermodynamic non-equilibrium and chemical non-equilibrium compiled by Professor Wang Baoguo and his group can complete the computation in this region.The distribution of flowfield shows agreement with each other,and values of corresponding parameter only have very limited difference.As we can see in the computation:when DSMC is being used,the computation time increases with the decrease of Knudsen number.Value of Kn1 can be got from this code,which is near 0.001 9.When Navier-Stokes is being used,the computation is more difficult to get convergence with a higher Knudsen number.Value of Kn2 can be got from this code,which is near 0.012 5.It has also been found that during the computation,for Knudsen number closed to Kn1 and Kn2 respectively,the use of DSMC and Navier-Stokes code will lead to a decrease of the convergence rate.There are three measures to accelerate the convergence which will be introduced in this paper.Because of the low Knudsen number characteristic region,all the flight cases of the reentry process could be completed by appropriate selection between DSMC and Navier-Stokes code.Obviously,this conclusion is very important for the numerical computation in reentry flight process.
Application of unstructured grids in numerically simulating ice accretions
ZHANG Qiang, GAO Zheng-hong, FU Lin
2011, 26(5): 977-983.
Abstract PDF(1141KB) icon1946 icon21
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Based on unstructured grids,the ice accretions on airfoils have been numerically simulated.The air flowfield was solved using the Euler equations.A permeable wall was used to simulate the droplet impingement on airfoils.An iterative method was developed to solve the governing equations for droplets.The collection efficiency was calculated from the droplet flowfield.The different freezing models corresponding to the rime and glaze ice were employed to simulate the freezing process.The process of ice accretions was simulated with the assumption that ice accumulates layer-by-layer and the ice shape was built with the assumption that ice grows in the direction normal to the airfoil surface.The rime and glaze ice accretions on a NACA 0012 airfoil were investigated and the comparison with the experimental data indicates that the numerical method proposed is effective.The effects of ice accretions on aerodynamic performance of the airfoil were also analyzed.
Application of parabolized Navier-Stokes equations into basic flows for stability analysis of hypersonic flows
LIU Jian-xin, YU Min, LUO Ji-sheng
2011, 26(5): 984-990.
Abstract PDF(948KB) icon1844 icon24
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By using streamwise pressure gradient on the edge of the boundary layer instead of that in the boundary layer,traditional solution for streamwise pressure gradient in parabolized Navier-Stokes (PNS) equations was improved and applied to PNS equations as basic flows for stability analysis of hypersonic flows.Three typical examples with flat,blunt cone at zero and small angle of attack,were calculated.For the blunt three-dimension flows or two-dimension flows,PNS equations are reliable to get the hypersonic basic flows for stability analysis,and the results of the stability analysis are in good agreement with those obtained by solving Navier-Stokes (N-S) equations directly,but expense of time and space is an order of magnitude lower than N-S equations.
Numerical simulation of gas-liquid two-phase flow in high temperature and high pressure supersonic cross flow
RUI Shou-zhen, XING Yu-ming, LIANG Cai
2011, 26(5): 991-996.
Abstract PDF(997KB) icon2231 icon25
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An Euler-Lagrange method was used to describe gas-liquid two-phase flow in high temperature and high pressure supersonic cross flow of gas-steam launching system.The gas phase flow field was simulated by solving the Navier-Stokes equations using RK (Runge-Kutta)-AUSM+ (advection upstream splitting method+) scheme.A particle trajectory model was used to represent the liquid phase.The source terms were added to the gas phase conservation equations to simulate the coupling of two-phase.Several applications were calculated to analyze the droplet evaporation and the influence on gas flow field and energy output.The conclusions are useful to design and optimize the gas-steam launching system and energy regulation.
Investigation on the ice-type microstructure characteristics of aircraft icing based on the fractal theories
DU Yan-xia, GUI Ye-wei, KE Peng, WANG Xun-nian
2011, 26(5): 997-1002.
Abstract PDF(1343KB) icon1836 icon22
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The ice-type microstructure characteristics of aircraft icing were investigated by combining icing tunnel and metallography tests based on the theories of fractal geometry.The fractal dimension of the ice-type microstructure was calculated by means of box-counting dimension method,and the relationship between the fractal dimension and the icing conditions was analyzed.The results indicate that the inflow temperature and velocity of the airflow have great influence on the fractal dimension of ice-type microstructure.The higher velocity or the lower the temperature means greater fractal dimension,and vice versa.Under the same icing conditions,the fractal dimension of runback icing is smaller than the leading edge icing.
Numerical investigations of two-phase spray combustion flow fields in slinger annular combustor
YAN Ying-wen, SONG Shuang-wen, HU Hao-sheng, WANG Yi-yang, LEI Yu-bing, ZHAO Jian-xing, LIN Zhi-yong
2011, 26(5): 1003-1010.
Abstract PDF(1414KB) icon1921 icon39
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In arbitrary curvilinear coordinates,numerical investigations of three-dimensional two-phase spray combustion flow fields for a slinger annular combustor were carried out.Three-dimensional body-fitted grids were generated by TTM (Thompson-Thames-Martin) method,k-ε model was used to simulate the turbulent viscosity;EBU (eddy break-up ) -Arrhenius combustion model,EDC (eddy dissipation concept) combustion model and SOM (second-order-moment) combustion model were applied to predict turbulent combustion rate.The gas and liquid phases were treated with Eulerian-Lagrangian method and the gas-liquid coupling was calculated with PSIC (particle-source-in-cell) arithmetic.The effects of different combustion models on two-phase spray combustion flow fields were studied.The numerical results are in good agreement with the experimental data.It shows that all of the combustion models are used to simulate the combustion process in slinger annular combustor,but the SOM combustion model and EBU combustion model are better than EDC combustion model for simulation of two-phase spray combustion flow fields in the slinger annular combustor.
Experimental investigation of heat transfer characteristic in turbine casing
ZHANG Shu-hua, ZHANG Li, ZHU Hui-ren, XU Du-chun
2011, 26(5): 1011-1016.
Abstract PDF(977KB) icon1769 icon20
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The heat transfer coefficient distribution of the turbine casing inner surfaces was studied experimentally by utilizing transient thermochromic liquid crystal technique.The casing investigated is composed of complex structure including impingement hole and dimples.Experiment results show that the jet impingement is a main contributing factor to heat transfer enlargement.The heat transfer coefficient near the exit hole and the impingement region is higher than others.The experiment results are helpful to the calculation of turbine casing temperature field and the control of blade tip clearance.
Three-dimensional thermoacoustic instability model based on spectral method
LI Lei, SUN Xiao-feng
2011, 26(5): 1017-1024.
Abstract PDF(1343KB) icon1842 icon44
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In order to investigate the effect of circumferential non-uniform fluid parameters and heat release on thermoacoustic instabilities, Chebyshev method was applied to axial and radial directions and Fourier method was applied to circumferential direction in the linear Euler equations. Resonant frequencies and acoustic fields of a duct were obtained by this method for validation and further investigations. At last, after some calculation for circumferential non-uniform heat release, it is verified that some symmetrical circumferential non-uniform conditions can be simplified to uniform conditions. But this approximation would bring errors if the circumferential non-uniform distribution is strong in case of asymmetrical distribution.
Numerical investigations on thrust augmentation mechanism of single ejection driven by two detonation tubes
ZHANG Huan-hao, CHEN Zhi-hua, SUN Xiao-hui
2011, 26(5): 1025-1030.
Abstract PDF(1181KB) icon1701 icon15
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Based on two-dimensional Euler equations,and in combination with the high-resolution hybrid Roe/HLL (Harten-Lax-Van Leer) scheme and adaptive mesh refinement method,numerical simulations of single ejection driven by two pulse detonation engines (PDE) were performed.The results show the propagation processes of the ejection of the primary detonation and the secondary detonation induced inside the ejector.After two detonation waves are ejected out,they propagate in the form of unexpanded jet flow,and interact with each other at the same time,postponing the ejection time of the exhausted gases and decreasing the absorption time of ambient air.As a result,the ejection efficiency of the ejector decreases,and the numerical results agree well with corresponding experimental results.
Experimental study on emission performance of rich-burn quick-quench lean-burn (RQL) trapped-vortex combustor
JIN Yi, HE Xiao-min, JIANG Bo
2011, 26(5): 1031-1036.
Abstract PDF(957KB) icon2101 icon24
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An experimental study focused on emission performance of trapped-vortex combustor (TVC) with liquid fuel under rich-burn quick-quench lean-burn (RQL) mode was performed.The effect of a variety of parameters on emission performance was obtained,such as excess air coefficient of cavity,airflow rate and inlet temperature.The results show that:CO and UHC (unburned hydrocarbon) volume fractions increase as the excess air coefficient of cavity increases (α=0.61~1.53) while NOx volume fraction decreases;the emission performance of the combustor gets worse as airflow rate(Wa=0.4~0.6kg/s)increases,CO,UHC and NOx volume fractions increase;CO and UHC volume fractions decline and NOx volume fraction rises with the increase of inlet temperature (283~473K).
Numerical simulation of detonation initiation in a duct via imploding annular detonation
QIN Ya-xin, GAO Ge
2011, 26(5): 1037-1042.
Abstract PDF(1218KB) icon1667 icon17
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Computational simulations on detonation duct with different annular pre-detonators were carried out to study the phenomena,mechanism and gas dynamics characteristic of annular detonation initiation.Two-dimensional axisymmetric and unsteady Navier-Stokes equations were numerically simulated,and detailed chemical reaction kinetics of hydrogen/air mixture was used.The results of numerical simulation show that laminar flame generated by low energy ignition in annular pre-detonator accelerates under the narrow channel,and then forms annular detonation via deflagration to detonation transition.Annular detonation detonates the combustible mixture in the main detonation chamber after reflection and imploding at the axis.Contrastive research on the distance and intensity of stable detonation was analyzed.Through calculation and analysis,it provided a deep understanding on the aerodynamics characteristic of annular detonation wave diffraction,reflection and imploding and the development of complex wave in the transitional region,laying a theory basis for detonation initiation and useful information to further experiment.
Experimental investigation on effects of flame jet ignition on deflagration to detonation transition in tube
YU Jun-li, QIN Ya-xin, GAO Ge
2011, 26(5): 1043-1047.
Abstract PDF(827KB) icon1670 icon19
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A detonative tube filled with acetylene and air by flame jet ignition was designed to study deflagration to detonation transition.The detonative tube was one end opened and the other end closed.A pre-combustion chamber was installed at the closed end perpendicularly to detonative tube.Flame jet produced by spark plug ignition in pre-combustion ignited the mixture in detonative tube.Flame propagation velocity in duct was measured by a system based on photoelectric transition principle.Compared with spark plug ignition in tube wall,flame jet ignition can increase initial velocity in the tube and reduce the distance of deflagration to detonation transition.Through the experiments of the deflagration to detonation transition process in different experimental conditions,the mechanism that flame jet ignition can reduce the distance of deflagration to detonation transition was discussed.
Simulation technique for the high temperature components in aero-engine
HOU Sheng-ping, TAO Zhi
2011, 26(5): 1048-1051.
Abstract PDF(880KB) icon1880 icon31
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The method to simulate the air system of jet engine was studied,and new approach was applied into the combined fluid area and solid area to predict the characteristic of high temperature components and the cooling air system of jet engine.The conservation equations of solid components and the cooling air system were solved in a coupled manner.The method was validated and then was applied to predict the characteristics of turbine disk in engine,and meanwhile the comparison between the simulated results from the strongly coupled method and the weakly coupled method was worked out.
Numerical study of tangential effusion cooling for combustor liner
WANG Tao, SUO Jian-qin, LIANG Hong-xia, WANG Rong-juan
2011, 26(5): 1052-1058.
Abstract PDF(1283KB) icon1908 icon17
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To solve technical difficulties resulting from high temperature rise and low emission of new generation engine combustor,a single tube combustor model with tangential effusion cooling technology was designed.Numerical simulation was conducted to study the flow field characteristics and wall temperature distribution of combustor liner by solving Navier-Stokes (N-S) equations with thermal fluid-solid coupling method.The liner wall temperature distribution was computed under two conditions by three-dimensional coordinate system,the fuel particle trajectory by Lagrange method,the combustion by non-premixed model,the radiation by discrete ordinates model,the turbulence by the standard k-ε model,and the neighborhood of the solid wall by the wall-function.The results show that,at the 0.046 fuel-air ratio condition,30% cooling air mass fraction,830K inlet air total temperature and 3MPa inlet air total pressure,the maximum wall temperature is 1015K and the maximum temperature gradient is 22.5K/cm,which meet the need of wall temperature level for 12 thrust-mass ratio military engines and low emission civil engines at 30% cooling air mass fraction,and 0.046 fuel-air ratio condition.
Numerical simulation of highly loaded multi-stage fan / compressor of a turbofan engine
JIN Dong-hai, GUI Xing-min
2011, 26(5): 1059-1065.
Abstract PDF(1074KB) icon2271 icon28
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According to high-altitude and low Reynolds number aerodynamic performance requirements of a turbofan engine, the fan/compressor on 0km and 21km operating conditions were simulated using three-dimensional (3-D) numerical simulation software Numeca. The results show that: the three-dimensional numerical simulation results of the 4-stage fan are in good agreement with the experimental results, and the precision can meet the engineering requirements; from 0km to 21km altitude, the inlet blade chord Reynolds number is reduced from 106 to 105, the mass flow rate is reduced by 2%~3%, the total pressure ratio is decreased a bit, and the efficiency is decreased by 3%; in the 3-D numerical simulation of 9-stage compressor, air bleeding is considered; from 0km to 21km altitude, the inlet blade chord Reynolds number is also reduced from 106 to 105, the mass flow rate and total pressure ratio are decreased a bit, and the attenuation of adiabatic efficiency increases from 4% to 7% with the decrease of speed.
Numerical analysis for the matching of the core driven compression system in a double bypass engine
ZHANG Xin, LIU Bao-jie
2011, 26(5): 1066-1076.
Abstract PDF(1331KB) icon1642 icon24
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The numerical analysis for the matching of the core driven compression system in a double bypass variable cycle engine was presented in this paper. The system consists of a one-stage-core driven fan stage (CDFS), an inner bypass duct and a five-stage high pressure compressor (HPC), providing two basic operating modes: the single bypass mode and the double bypass mode. Variable vanes are necessary to realize the mode switch of the system. The correct matching in the double bypass mode requires a proper combination of the mass flow, total pressure ratio and blade speed. The work capacity of the system decreases in the double bypass mode and the pressure ratio tends to decrease more for the CDFS and the front stages of the HPC. The overall system efficiency is higher in the double bypass mode. The radial distributions of aerodynamic parameters are similar in different modes. The notable redistribution of mass flow downstream the CDFS in the single bypass mode leads to strong radial flows and additional mixing losses. The absolute flow angles into the inner bypass increase for the inner span and decrease for the outer span when the system is switched from the single bypass mode to the double bypass mode.
Fluid-structure interaction and flutter analysis of compressor blade based on CFD / CSD
WANG Zheng, WU Hu, SHI Ya-feng, YANG Jin-guang, CAI Jin
2011, 26(5): 1077-1084.
Abstract PDF(1355KB) icon1916 icon34
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For the most important flutter problem of turbomachinery blades,the fluid-structure interaction (FSI) problems and flutter characteristic of turbomachinery blades were studied in present paper based on the CFD/CSD (computational fluid dynamics/computational structural dynamics) algorithm.The three-dimensional unsteady Navier-Stokes equations and three-dimensional structural model were solved by the finite volume method and the finite element method,respectively.High accuracy in calculation and data exchange were gained by using load transfer,deformation tracking and synchronization between two solvers.The procedure successfully simulated the aeroelastic responses of a high performance fan rotor,NASA (National Aeronautics and Space Administration) Rotor 67,under a range of operational conditions,and the results were compared with the experiment.The results show that the flutter mechanics of the compressor blade could be illustrated based on the distribution of cycle work and mean pressure,which is helpful to the decision of compressor stability.
Effect of different axial spacing between blade rows on transonic axial compressor performance
SHI Ya-feng, WU Hu, CHEN Li-xin, WANG Zheng, YANG Jin-guang, LI Mi
2011, 26(5): 1085-1091.
Abstract PDF(1367KB) icon1733 icon22
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The steady flow field of a transonic axial compressor under design rotation speed was numerically simulated,proving that the close spacing between upstream stator and rotor can largely reduce the efficiency and pressure ratio,however the close spacing between rotor and downstream stator can improve the efficiency and pressure ratio.The unsteady numerical simulation indicates: (1) the close spacing between upstream stator and rotor can enlarge the interaction of rotor shock on the stator wake,causing the deterioration of performance; (2) the wake recovery effect under the close spacing between rotor and downstream stator decreases the mixing loss,thus slightly improving the performance.
Application of AUSM + method into simulation of viscous internal flows
JIANG Xiao-song, LIU Jian-jun
2011, 26(5): 1092-1098.
Abstract PDF(1129KB) icon1577 icon20
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The AUSM+ (advection upstream splitting method+) and one-equation Spalart-Allmaras (S-A) turbulence model used in the present in-house three-dimensional Reynolds averaged Navier-Stokes (RANS) flow solver were briefly described.The transonic flow in the Sajben converging-diverging duct and the flow in the stator passage of a high turning turbine were simulated to verify the code.The results show that the present solver can be used to simulate accurately the complex internal flow fields.
Two-stage turbocharging matching of light aero-engine at high altitude
WANG Yan-hua, LI Yun-qing, CHEN Xiao-long, LI Bo
2011, 26(5): 1099-1103.
Abstract PDF(937KB) icon1806 icon25
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In order to operate the light aero-engine without power loss at altitude 10km,two-stage turbocharging was required to keep the intake air density at in plenum different altitudes the same as that at sea level.AVL-Boost model was built to simulate the working process of single-stage turbocharging engine and the model was verified through relevant experiments.Based on the primary model,the two-stage turbocharging model was built.Considering the effect of Reynolds number on small size centrifugal compressor at high altitude working condition,the matching operating points of each stage compressor were found.The simulation calculation result shows that the matching scheme is suitable for the engine and could achieve design requirements.
Modified blockage model of tip leakage flow and its validation
CHENG Zhao-qing, CUI Jian, LI Zhi-ping, GONG Yi-fang, LI Qiu-shi
2011, 26(5): 1104-1110.
Abstract PDF(1126KB) icon1773 icon16
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Based on the common cognition of the tip clearance flow,which has a significant influence on compressor performance and MIT (Massachusetts Institute of Technology) Khalid tip leakage model,a blockage model of tip leakage flow in the condition of low-speed and transonic was deduced in this paper.With analysis of the real flow case in tip clearance and diffusion passage,the aerodynamic design parameters,such as loading,cord length,etc,on the rotor tip and the influence of shock wave on tip leakage loss were analyzed in this model.The three-dimensional numerical simulation results show that this model can track the behaviors of jam resulted from compressor tip clearance flow.
Investigation of a new combined type compressor's feasibility
LU Wen, NIE Chao-qun, LIN Feng
2011, 26(5): 1111-1117.
Abstract PDF(1210KB) icon1547 icon15
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The purpose of this research is to present a new concept of fluid compression, by combining characteristics of displacement compressor and impeller compressor.And as background, this paper carried out theoretical analysis, numerical simulation, and experimental verification work. The results show that this new type compression has both advantages of displacement compressor and impeller compressor. And its stability is similar to the displacement compressor, but it has smaller volume than displacement compressor at the same mass flow rate; and higher pressure ratio and efficiency than impeller compressor.
Technique for diagnosing fault of rotor vibration based on improved fuzzy SVM
AI Yan-ting, FEI Cheng-wei, WANG Zhi
2011, 26(5): 1118-1123.
Abstract PDF(1052KB) icon1890 icon18
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A fuzzy support vector machine (FSVM) fault diagnosis method was proposed based on improvement of the ordinary diagnosis method used to determine memberships,and an improved diagnosis mathematical model was established.Then,four kinds of typical rotor vibration faults were simulated on a rotor vibration experimental rig,and effective samples of fault were collected.Finally,the validity and feasibility of this method used for rotor vibration fault diagnosis were validated by calculating and analyzing the obtained examples.
Methods for test and state analysis of determinate simulation results
FU Hui-min, WU Wen-juan
2011, 26(5): 1124-1127.
Abstract PDF(959KB) icon1593 icon17
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In order to judge whether the simulation results are right or not, the method for test of determinate simulation results with equal variation coefficient was established. Furthermore, the methods for state analysis of determinate simulation results with equal variation coefficient or equal variance were established, which can analyze every state of the simulation results and determine which states are simulated correctly and which are not. In this way, the method can guide the programming of simulation software.
Prediction for constitutive relationship of metallic rubber based on BP neural net
LI Yu-yan, HUANG Xie-qing, LI Fu-lin
2011, 26(5): 1128-1134.
Abstract PDF(1011KB) icon1600 icon21
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Coefficients of constitutive relationship for metallic rubber were studied and trained by BP (back propagation) neural net.BP neural net was introduced elaborately,and how to predict coefficients of constitutive relationship by BP neural net was discussed.BP neural net parameters were chosen.Through parameter identification of static experimental data of metallic rubber,BP neural net models were obtained in two cases,including:various densities,various shape factors and densities;and further prediction for the nonlinear constitutive relationship was realized.The experiments prove that the theory agrees with the experiment,indicating that the method of predicting nonlinear constitutive relationship of metallic rubber is feasible.
Research on vibration absorber for a super-high speed rotor system
CHEN Wei, DU Fa-rong, DING Shui-ting, HAN Shu-jun, LI Yun-qing
2011, 26(5): 1135-1141.
Abstract PDF(1125KB) icon1811 icon18
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A kind of freely assembled dry friction vibration absorber was presented to solve the problems of instability and rubbing faults for a super-high speed rotor system based on theory of dry friction dissipating energy from rotor vibration.In this structure,a wave-shaped elastic pad and some dry friction pads were freely assembled on shaft,and axial normal force was provided for elastic pad and dry friction pads by pre-loaded moment for nut.When friction pads moved with shaft,the relative movements between them could dissipate vibration energy from rotor system,absorb vibration and enhance system stability.The configuration format meeting the stability in engineering for the damper of the studied rotor system has been acquired by testing different groups of dry friction pads and pre-loaded moment.The results show that dry friction damper is suitable for high speed and light loaded rotor system to restrain vibration and enhance its stability.The testing routine is helpful to find a comfortable configuration format in engineering of dry friction damper.
Dynamical analysis on shell structure made of C/C-SiC composite materials
ZHANG Da-yi, HONG Jie, REN De-xin
2011, 26(5): 1142-1147.
Abstract PDF(1211KB) icon1735 icon17
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An effective engineering method was put forward to solve the dynamical problems of a ramjet combustion chamber liner made of C/C-SiC composite materials,in the absence of mechanical performance parameters of materials.The finite element model of liner was erected,and natural characteristics and vibration responses caused by random excitation were calculated.Then the design level was evaluated based on dynamical thesis.The study has a great reference value for vibration analysis on shell structure made of composite materials and dynamical design on shell structure used in ramjet.
Research on influence of typical microstructure characteristics of Ni base single crystal on creep rupture and deformation analysis of turbo blade
CAO Juan, WANG Yan-rong, SHI Duo-qi
2011, 26(5): 1148-1158.
Abstract PDF(1289KB) icon1304 icon15
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Considering the influence of typical microstructure characteristics on creep performance,a series of UM-F single crystal alloys which had similar element components but different microstructures were used to analyze the relationship between creep life and microstructure characteristics of Ni base single crystal.Three main factors were proposed:misfit,volume fraction of precipitate and maximum matrix channel width.The Microstate parameter Ymicro was established to estimate the deformation state of the materials.The linear relationship between the initial value of microstate parameter Y0 and creep life under a certain temperature/load was affirmed.By analyzing the high temperature region of turbo blade using the material parameters of DD3,the creep deformation and the life prediction of the critical points of blade were obtained and the result closed to the test.
Numerical study of particle damping in two dimensions by use of discrete element method
TANG Wei, WANG Yan-rong, WANG Xiang-ping, YANG Jian-qiu
2011, 26(5): 1159-1165.
Abstract PDF(1176KB) icon1692 icon18
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The physical model of particle damping in two dimensions was developed for the cavity with particles inside located at the free end of an L-shaped beam,and discrete element method (DEM) was used to investigate the effects of two-dimensional cavity sizes on particle damping.The results show that: (1) the highly nonlinear particle damping,which is at least one order of magnitude higher than the intrinsic material damping of metals,can significantly suppress the vibration of structures;(2) when dimensionless acceleration amplitude Γ<1,particle damping is very small;however,when Γ>1,it firstly increases and then decreases with the increase of Γ,indicating that there is a critical dimensionless acceleration amplitude for the highest damping;(3) the peak value of particle damping increases and appreciably shifts to the lower Γ with the increase of horizontal dimensionless impact clearance.However,it also increases but shifts to a higher Γ with the increase of vertical dimensionless impact clearances.The simulation results agree well with the experimental data,and can be applied to the practical design of a particle damper.
Adaptive PID control for flexible rotor supported by active magnetic bearings based on single neuron with varying learning rates
ZHUANG Hua-qiang, XIE Zhen-yu, ZHANG Shu-ying, WU Kai-feng, SHI Qing-cai
2011, 26(5): 1166-1171.
Abstract PDF(1105KB) icon1730 icon18
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To satisfy the requirements of active magnetic bearing system that operates on both low frequency and high frequency,the signal of the rotation speed was introduced into the control based on normal single neuron PID (proportion integration differentiation) control,and different learning rates at varying rotation speeds were selected to adjust the control parameters and obtain the active magnetic bearings with suitable stiffness and damping.The experimental results show that adaptive PID control based on single neuron with varying learning rates can reduce vibration of the rotor obviously at critical speeds,and help the system operate safely.
Establishment of aero-engine state variable model based on linear fitting method
LU Jun, GUO Ying-qing, CHEN Xiao-lei
2011, 26(5): 1172-1177.
Abstract PDF(1009KB) icon2292 icon37
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According to the initial value problem in establishment of aero-engine small perturbation state variable model based on nonlinear fitting method,a linear fitting method against this problem was proposed.The objective function,in which the model outputs are linear functions of system matrix,was constructed by means of the known state sequences in discrete domain,resulting in transformation from nonlinear least square problem to linear least square problem.The method was applied to establish the small perturbation state variable model for a turbofan engine and then compared with nonlinear fitting method.The results show that its effectiveness not only avoids the initial value problem but also obtains better modeling precision.
Gaussian weighted sum clustering method of adaptive hybrid diagnostic model for turbo-shaft engine
SHE Yun-feng, HUANG Jin-quan, LU Feng
2011, 26(5): 1178-1184.
Abstract PDF(1167KB) icon1811 icon16
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A Gaussian weighted sum clustering method of on-board adaptive hybrid model was proposed for health parameter estimation of turbo-shaft engine in the full flight envelope.The on-board adaptive hybrid model was composed of Kalman filter and neural network.Gaussian weighted sum model was used to cluster a huge amount of flight data in real-time and update the neural network weighting.The working range of adaptive hybrid model was increased automatically with this method.The simulation results show the validity of the proposed method.Adaptive hybrid model based on Gaussian weighted sum clustering increases the accuracy for turbo-shaft engine performance tracking in the full flight envelope.
Dynamic characteristics analysis of bump foil journal bearings with air lubrication
XU Huai-jin, LIU Zhan-sheng, LV Wei-jian, LI Hua-feng
2011, 26(5): 1185-1193.
Abstract PDF(1658KB) icon1914 icon26
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Differential equations of air film in elastic bump foil journal bearing were deducted by the perturbation method with air lubrication Reynolds equation and series expansions of air film,air film thickness and foil deformation.The mathematics model of the relations among air film thickness,bump foil deformation and air film pressure was developed in consideration of air compressibility.Both finite difference method and Newton-Raphson method were applied to solve the coupled differential equations and air film thickness mathematics model equations,while the variation rules of air film stiffness and damping coefficients were achieved with different eccentricities,speeds,perturbation frequencies and different length-diameter ratios.This provides a basis for bump foil journal bearing design,optimization and theoretical and test analysis of rotor-elastic foil bearing system.The numerical results show that the main air film stiffness is enhanced when eccentricity and speed increase,and the value of air film stiffness and damping of bump foil journal bearing are connected strongly with the perturbation frequencies.
Automatic feedback correction and deviation analysis for tooth surface of spiral bevel and hypoid gear
LI Tian-xing, DENG Xiao-zhong, LI Ju-bo, YANG Jian-jun
2011, 26(5): 1194-1200.
Abstract PDF(1171KB) icon1861 icon22
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Based on the measurement information of tooth surface,the deviations and influential factors were identified and analyzed,and the corresponding relations between the machine-tool motion parameters and the tooth surface deviation were derived.An automatic identification system was developed to determine the deviation type and the corrected items of machine-tool motion parameters.By the model of 4-axis computerized numerical control (CNC) cutting machine and the application of numerical optimization method,the automatic correction and feedback were realized via the network between the measuring center and the cutting machine.Experiments and applications show that the expected results of effective reduction of tooth surface deviation can be achieved,the tooth surface accuracy can meet the design requirements,and the digital closed-loop manufacturing of spiral bevel and hypoid gear can be carried out effectively by means of automatic feedback correction of machine-tool motion parameters and automatic identification of tooth surface.

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