2013 Vol. 28, No. 2

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Vibration analysis of two-piece inner ring angular contact ball bearing with elastic support
DENG Si-er, YAN Ya-chao, WANG Yan-shuang, YANG Hai-sheng
2013, 28(2): 241-251.
Abstract PDF(3063KB) icon3467 icon2038
Abstract:
Taking the bearing with elastic support as the object of study,nonlinear dynamics differential equation for the two-piece inner ring of angular contact ball bearing with elastic support,which coupled the outer ring and housing,was established.Fine integral method and predict-correct Adams-Bashforth-Moulton multi-step method were used to solve the nonlinear dynamic equations,and the vibration characteristics of two-piece inner ring of angular contact ball bearing with elastic support were analyzed and discussed.The analysis results show: (1) Magnitude of inner vibration can be significantly decreased from increasing the number of the groove joint.The thickness of the sleeve has small effect on inner vibration,and with the increase of the thickness,the amplitude value of the inner decreases first and then increases. (2) When the axial load has a small value,it is more helpful for decreasing the magnitude of bearing vibration when increasing the number of the groove joint.On the contrary,under the heavy axial load,it is beneficial for the stabilization of bearing when reducing the number of the groove joint. (3) There is a reasonable number of groove joints and thickness of sleeve for elastic support to obtain the minimum radial vibration amplitude of the bearing.
Experimental setup for testing thermo-mechanical fatigue of single crystal turbine blades
WANG Rong-qiao, JING Fu-lei, HU Dian-yin
2013, 28(2): 252-258.
Abstract PDF(1363KB) icon2619 icon1610
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An experimental system including 5 subsystems:the loading,heating,air cooling,water cooling and control subsystems,was constructed to satisfy the requirements of thermo-mechanical fatigue (TMF) experiments of single crystal hollow turbine blades.The TMF experimental system provided evidences that the stress distribution,temperature distribution,air cooling and stress/temperature spectrum on critical section of turbine blades under service conditions could be simulated simultaneously in a laboratory environment.And the TMF experiments were performed on the critical section.The results of the TMF experiments reproduced the failure model of the turbine blades.Based on these results,life prediction and failure analysis could be investigated.
Adaptive unscented incremental filter method
FU Hui-min, WU Yun-zhang, LOU Tai-shan
2013, 28(2): 259-263.
Abstract PDF(325KB) icon1939 icon1271
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The adaptive unscented incremental filter(AUIF)model was put forward, in which its concept, model,basis equations and the recursive calculative steps were established. Classical filters did not research the system errors of measurement equations. Due to environmental factors and the instability of measurement equipments, it is difficult to accurately obtain the measurement equations that are not verified and calibrated. So the measurement data have unknown time-varying system errors in actual engineering in the actual environment (such as deep space exploration). The model equations and the noise characteristics have many uncertainties. The uncertainty will lead to greater Kalman filtering error and indeed diverges. The presented AUIF can successfully eliminate the measurement equation system errors. The method can estimate statistical characteristics, adjust gain matrix in real time and greatly improve the filtering accuracy. The method is simple to calculate and easy to apply in engineering.
Fatigue fracture mechanics of forged TC4 alloy joints by electron beam welding
QI Hong-yu, LI Shao-lin, YANG Xiao-guang, WANG Xiang-ping, SU Shou-li
2013, 28(2): 264-269.
Abstract PDF(1285KB) icon1971 icon1409
Abstract:
Stress controlled high-cycle fatigue (HCF) test and strain controlled low-cycle fatigue (LCF) test for electron beam welding (EBW) joints of forged TC4 alloy were investigated at room temperature.Fracture surfaces were observed by scanning electron microscope (SEM),and the crack initiation mechanism of fatigue failure was analyzed.The results show that all HCF specimens are fractured in the base material (BM) observed by SEM,while LCF specimens are mainly ruptured at fusion zone (FZ) and BM.Due to low stress level in HCF test,the crack of joints is initiated near the surface,while the crack of the joint in LCF test is initiated not only near the surface but also in the interior defects.The crack initiation mode depends on the load.
Bayesian sequential test method for probability of success of binomial distribution based on posterior probability
HAN Feng, LU Xi-cheng, LIU Yu, WANG Jian-guo
2013, 28(2): 270-274.
Abstract PDF(242KB) icon2198 icon1541
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A sequential test method based on Bayesian posterior probability was proposed to perform tests of hypotheses about probability of success of binomial distribution in complicated hypothesis conditions. The decision rules were constructed and the method for calculating the criterion value was given. For a given maximal sample size, the truncated method of the judge criteria was discussed for hypothesis test. At last, an example illustrated the proposed method and the result was compared with classical methods. The result shows that the sample number determined by the proposed method can be much smaller than that determined by classical methods on the condition of given prior probability.
Parallel dynamic model of rubber isolator about five-parameter fractional derivatives
TANG Zhen-huan, LUO Gui-huo, CHEN Wei, YANG Guo-hui, FANG Jian-min
2013, 28(2): 275-282.
Abstract PDF(1300KB) icon2150 icon1389
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The dynamic model of nonlinear fractional derivatives was established for the research of an auxiliary power unit(APU) rubber isolator.The parallel model of five-parameter fractional derivative was presented,which concerned frequency and amplitude dependencies.The model can simulate viscoelastic properties in a wide range with few parameters.At the same time,the influence of every parameter on dynamic modulus and loss modulus as well as the methods of numerical solution were studied.The result shows that the model can be used to predict the dynamic properties in a wide range.It provided basis for design and application of rubber isolator.
Variable precision rough set decision-making method for health assessment of aero-engine
YANG Zhou, JING Bo, ZHANG Jie
2013, 28(2): 283-289.
Abstract PDF(316KB) icon1916 icon1357
Abstract:
In order to solve the problems of variable working condition,non-linear and small sub-sample in the process of aero-engine health assessment,a variable precision rough set decision-making method based on the similarity measurement was proposed.Firstly,the principle and method of choosing value was given,and the decision-making rules were extracted.Secondly,the method of calculating attributes' relative importance based on cross-entropy was proposed and attributes' objective weights were given.Taking the expert experience and working experience into account,overall weights were formed.Finally,a weighted similarity measurement based on the overall weight of attributes was developed.By comparing the similarity degrees between the current object and other objects from the reduced decision-making system,the decision results were given.Simulation results show that the method is effective to aero-engine's health assessment with the help of expertise and running environment.In addition,the proposed method can be applied to other regions.
Combined heating method of low speed and high/middle temperature gas flow for thermal test of tip wedge structure
DONG Su-jun, LI Zhi-jie, WANG Jun
2013, 28(2): 290-296.
Abstract PDF(925KB) icon2354 icon1858
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The big temperature gradient in hypersonic tip wedge structure was calculated and simulated,and key thermal simulation parameters were presented.Since the single spout heating method can not simulate the heat flux density satisfactorily on the rear plate,a dual-mode heating method was developed to solve this problem,covering a high temperature flow with small spout in the center enveloped by a lower temperature flow.A typical hypersonic condition was simulated using CFD method.It shows that this new heating method can accurately simulate the hypersonic heat flux distribution of the tip wedge by effectively meliorating the heat flux distribution on the rear plate and maintaining the high heat flux density on the stagnation zone.The simulation of transient temperature distribution and big temperature gradient in the interior of tip wedge structure also gets very good results to support this strategy.Meanwhile,the dual-mode heating method can not only greatly reduce the spout size and speed of high temperature flow,but also greatly improve the test ability of electric arc wind tunnel to satisfy larger size of tip wedge structure.
Reaction kinetic numerical simulation of combustion process and emission formation in aero-engine combustor
MA Hong-an, XIE Mao-zhao, ZENG Wen, CHEN Xiao-xiao
2013, 28(2): 297-306.
Abstract PDF(2064KB) icon6759 icon3551
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A detailed mechanism and a reduced reaction mechanism (including 50 species and 118 reactions) of n-decane which was chosen as a surrogate fuel for kerosene were built.The ignition delay time of this surrogate fuel in the shock tube and the process of premixed combustion in the premixed burner were simulated by adopting the detailed and reduced reaction mechanisms,and the simulated results were compared with the experimental data.Furthermore,the flow characteristics and the reaction kinetic characteristics of combustion process and the formation of emissions and active species in a tube of the annular tube combustor were analyzed by combining this reduced reaction mechanism with the CFD computational software(Fluent),and the computational results were compared with that of the global reaction mechanism of C12H23 fuel.The results show that the ignition delay time,the shape of the profiles of the mole fractions of the reactants,the major combustion products simulated using the reduced mechanism agree well with the experimental data.Furthermore,compared with the global reaction mechanism of C12H23 fuel,when adopting the reduced reaction mechanism of n- decane,temperature field accords well with the practical situation,and the computational outlet temperature is closer to the design outlet temperature of the combustor.At the same time,the process of fuel low temperature decomposition and formations of pyrolysis products,active species and main emissions are better detailedly understood.
Experiment on spray characteristics of periodic air-assist direct injection atomizer
WU Ze-jun, HE Xiao-min, ZHU Zhi-xin, JIN Yi, DING Guo-yu
2013, 28(2): 307-315.
Abstract PDF(1671KB) icon1879 icon1433
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An experimental study on spray characteristics of a typical periodic air-assist direct injection atomizer was presented.Attention was focused on the effect of a series of parameters (such as duration of fuel injection,space time,duration of air injection and pressure of air) on spray characteristics.The fuel employed was RP-3,and the medium employed was compressed air.Laser particle analyzer was employed for spray measurement.Duration of fuel injection,space time and duration of air injection was changed from 2ms to 8ms,-2ms to 5ms,and 2ms to 8ms,respectively.The range of air pressure provided was 0.1～0.65MPa .The results show that the performance of atomization is improved as the ratio of air and fuel is increased.The increase of air density and space time is also benificial for atomization.Additionally,the distribution uniformity index value may be greater while the range of drop-size spreads more widely and the mean diameter is higher.For condition of high pressure,mean drop size is correlated using empirical equations.
Air-throttling effect of scramjet combustion characteristics
DENG Wei-xin, LE Jia-ling, WANG Xi-yao, YANG Shun-hua, ZHANG Wan-zhou, XU Ming-heng
2013, 28(2): 316-323.
Abstract PDF(1363KB) icon1918 icon1345
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Compressed air was introduced into the combustor to establish pre-combustion shock train.The main purpose of air throttling is to optimize flow structure of isolator and combustor to reduce the local flow velocity,increase the pressure and make ignition and combustion easier.Using CFD method,the cold and reactive flow fields with/without air throttling were compared.The results show that the throttling shock enlarges low momentum regions and slows down the air/fuel mixture.The flow distortion caused by the throttling shock and extended residence time enhance air/fuel mixing remarkably.The mixing efficiency increases from 40% to 85%.Also the combustion efficiency increases from 10% to 60%.A parametric research was conducted to investigate the effect of throttling location and throttling mass flow rate on the combustion characteristics.Three throttling locations,x=785mm,x=1000mm and x=1100mm,and three throttling mass flow rates with 10%,15%,30% were studied respectively.The results show that the effect of the nearest throttling location is most notable,where the least throttling mass is required.30% throttling mass flow rate increases back pressure sharply and makes the flow choked.In the given condition,throttling with 15% air flow mass at x=785 mm obtains the best combustion efficiency.
Numerical investigation of combustion flow fields in low heating value fuel cannular combustor
HE Min, CAI Wen-xiang, ZHAO Jian-xing, JI Hong-hu
2013, 28(2): 324-330.
Abstract PDF(1398KB) icon2236 icon1465
Abstract:
Combustion flow fields of a cannular combustor were calculated using arbitrary curvilinear coordinates for two low heating gas fuels with different chemical species.One fuel was natural gas mixed into nitrogen,and the other fuel was carbon monoxide.Predictions indicate that the chemical reaction rates of low heating gas fuels are directly related to chemical species. The combustion efficiency of the gas fuel carbon monoxide is higher than that of nature gas mixed into nitrogen. The effects of different chemical species of low heating gas fuels on combustion efficiency and outlet temperature are considerable.Therefore,it is very important to choose appropriate low heating gas fuels.The calculated combustion efficiency and outlet temperature distributions are in reasonable agreement with the measurements.These comparisons show that the mathematical models and numerical method are reasonable,and the numerical procedure is reliable and may be applied to the optimization design of the low heating value fuel cannular combustor.
Flow separation control of lobed ejector/forced mixer by ventilation
PAN Cheng-xiong, ZHANG Jing-zhou, SHAN Yong, WANG Xian-wei
2013, 28(2): 331-337.
Abstract PDF(1580KB) icon1915 icon1106
Abstract:
To control flow separation inside the lobed mixer with a big lobed angle, ventilating treatment was performed on a baseline lobed mixer to reveal the effectiveness of ventilation on eliminating separation bubble inside the lobed mixer when secondary flow is forced or ejected by numerical simulation. Results show that:(1)When the lobed angle is below 35 degrees, no separation is observed; when the lobed angle is at 35 degrees, separation bubble begin to appear inside the lobed nozzle, when the lobed angle is above 35 degrees, separation bubble augments.(2)Ventilating treatment on lobed forced mixer with a big lobed angle is able to eliminate the separation bubble inside the nozzle.(3)The same treatment on the other hand does not banish the separation bubble inside the lobed ejector mixer with a big lobed angle. In fact,the ventilating gap brings forward the separation phenomena rather than avoiding it.
Numerical investigation on vortex structure and jet mixing mechanism in lobed mixer
YUE Wei, LEI Zhi-jun, SU Shang-mei, ZHU Jun-qiang
2013, 28(2): 338-347.
Abstract PDF(2227KB) icon1916 icon1397
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With computational fluid dynamics software ANSYS CFX,the three-dimensional steady numerical simulation was conducted on the jet mixing flow of lobed mixer to study the formation mechanism and development process of the vortex structure,and its functional mechanism of the forced jet mixing.The results show that based on the SST(shear stress transport) model,the closed N-S equation can simulate the jet mixing process in lobed mixer excellently.While the streamwise vortices induced by the special geometry of lobed mixer depend on an indirect way of twisting the interface between core and bypass flow to accelerate the jet mixing process,normal vortices formed on the promotion of K-H(Kelvin-Helmholtz) instability accelerate the jet mixing directly.The passage vortices are produced by the interaction between the radical inward secondary flow and the low momentum fluid along the wall moving toward the lobe's crest where the passage vortices have an obvious promoting effect on jet mixing.Under the radical pressure gradient within the lobed mixer,boundary layer cut by lobe's leading edge rolls up along the surface of the lobe and forms the horseshoe vortex,and it has little effect on jet mixing.
Flow field characteristics of side-mounted subsonic inlet of the UAV
XIA Yang, LI Bo, WANG Hai-peng
2013, 28(2): 348-355.
Abstract PDF(1316KB) icon1781 icon1121
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A side-mounted diverterless subsonic inlet of the UAV(unmanned aerial vehicle) was designed and the flow field was simulated.The design methodology of the bump was presented and the characteristics of the inlet were obtained.The results show that angle of attack and yaw angle have little effect on the inlet's performance within 0°～8°.The total pressure recovery of the inlet is great than 0.965 and the distortion index is less than 0.253 under all states.The inlet meets the requirements of the engine,proving that the side-mounted diverterless subsonic inlet is feasible.It has also been found that there exists a higher pressure region on the bump surface than that on the fuselage for the diverterless subsonic inlet.The effect of pushing boundary layer aside for the bump is related to the fuselage profile,lip,relative positon of the entrance and flight conditions.The leading curve of the bump should not be too sharp for side-mounted inlet and a curved surface is better than a flat one in pushing the boundary layer away.
Performance of simple/recuperation cycle gas turbines under variable conditions
ZUO Zhi-tao, SUN Zhi-gang, ZHU Yang-li, CHEN Hai-sheng, TAN Chun-qing
2013, 28(2): 356-364.
Abstract PDF(4005KB) icon2160 icon1232
Abstract:
Off-design performance of simple and recuperation cycles was studied with calculation,analysis and comparison by means of gas turbine modelling technique and the models were solved by Newton-Raphson method.Main conclusions are as follows.Under the same operating parameters,the simple cycle gas turbine can provide more power output than the recuperation cycle one,while the latter is more efficient than the former.The efficiency of the recuperation cycle decreases faster than the counterpart as the turbine inlet temperatures decrease.For both cycles,the power outputs and efficiencies of gas turbines increase,but the compressor surge margins decrease with the drop of ambient temperature.The power outputs,efficiencies and compressor surge margins of gas turbines increase with the rise of ambient pressure.The above conclusions can provide good references for the off-design operation of aero-engine derived land-borne turbine generators.
Viscosity effect of hypersonic inlet based on magnetohydrodynamic control
HE Miao-sheng, YANG Wen-jiang, ZHENG Xiao-mei, LIU Yu
2013, 28(2): 365-371.
Abstract PDF(1490KB) icon1839 icon1148
Abstract:
Two-dimensional steady-state flow equations coupled with low Reynolds number MHD(magnetohydrodynamic) effects were solved with MHD equations to study the viscosity effects of a MHD controlled hypersonic forebody/inlet.The numerical results showed some typical characteristics of viscous flowfield at the inlet when flight Mach number was larger than the designed value.Furthermore,the viscosity effect of inlet with MHD interaction was taken into discussion.The result analysis indicates that shock-induced boundary layer separation at the inlet can be restrained,and the maximum temperature near the interface of the inlet can be significantly lowered by implementing MHD control.Additionally,it is particularly true that the flow and performance parameters of MHD controlled inlet profiles versus magnitude force of the magnetic are fairly different when the viscosity is taken into consideration.
Research and application of cycle parameter optimization algorithm for high bypass ratio turbofan engine
CAO Ming-dong, WANG Zhan-xue, CAI Yuan-hu, LIU Zeng-wen
2013, 28(2): 372-378.
Abstract PDF(772KB) icon1999 icon1641
Abstract:
To investigate the high bypass ratio turbofan propulsion cycle optimization utilizing the multi-constraints and multi-optimization variables,a self-adaptive three times variation differential evolution (STTVDE) was developed and verified by the Benchmarks multi-peak functions.The turbofan propulsion cycle parameters with multi-constraint parameters were optimized by incorporating STTVDE with the aero-engine performance program.The results demonstrate that the convergence precision of STTVDE is higher and the convergence speed of STTVDE is faster in comparison with differential evolution (DE).Besides,applying STTVDE,the efficiency of cycle parameter optimization is improved markedly. Therefore,the proposed method is considered as a promising method for turbofan propulsion cycle parameter optimization.
Aerodynamic characteristics of waverider and its integrated configuration with blunt leading edge
CHEN Xue-dong, WANG Fa-min
2013, 28(2): 379-384.
Abstract PDF(1060KB) icon2277 icon1196
Abstract:
The maximum lift-drag ratio was used as the optimization target,and a waverider configuration from the conical flow field was designed.To meet the needs of heat protection,a waverider configuration with blunt leading edge was designed.Numerical and experimental methods were used to analyze the aerodynamic characteristics of blunt waverider configurations.The results show that with the blunt radio increasing, the lift of blunt waverider increases 2% and the drag of blunt waverider is nearly 3 times larger than that of the sharp waverider, as well as the ratio of lift to drag of blunt waverider is 50% of that of the sharp waverider. For blunting waverider configurations, the high lift-drag radio characteristics is kept both on and off design conditions.The 2-D inlet was used as the basis,and a waverider/inlet integrated configuration from the muti-wedge-cone flow field was designed.Blunt-leading design was conducted for the integrated configuration.The results from the numerical analysis show that the ratio of lift to drag of this configuration is greater than 2.6, and the total pressure recovery of the inlet is almost 40%, which can meet the requirements of inlet.
Transition state performance simulation of air-turbo-ramjet engine
LI Cheng, CAI Yuan-hu, TU Qiu-ye
2013, 28(2): 385-389.
Abstract PDF(511KB) icon2019 icon1543
Abstract:
In order to simulate the transition state performance of air-turbo-ramjet(ATR)engine,an ATR engine model was established.The ATR engine fuel feeding law and the acceleration/deceleration performance were obtained through comparing to the traditional turbojet fuel feeding principle.The result shows that the ATR engine is more flexible in the selection of fuel feeding law and would satisfy the requirement of surge margin better.The engine start process could be simulated by this model after adding low speed of rotation characteristic according to the charateristic of ATR engine.
Boundary conditions and Fourier series truncation errors with 3-D inverse method for radial and mixed flow turbomachines
TIAN Xiao-pei, SHAN Peng
2013, 28(2): 390-400.
Abstract PDF(2204KB) icon1689 icon1346
Abstract:
Different kinds of the inlet and outlet boundary conditions were studied in theory and different specifications of the endwall boundary condition were compared. The impacts of the inlet, outlet, endwall boundary conditions and the series truncation errors on the blade design by a steady Reynolds averaged Navier-Stokes (RANS) solver were studied numerically. The results show that the impacts of the inlet and outlet boundary conditions on the blade design are neglectable, while those of the endwall boundary conditions are relative large. The impacts of the series truncation errors could be neglected if the number of Fourier series terms is more than 15.
Direct numerical simulation of NACA0012 cascade flow at low Reynolds number
ZHU Hai-tao, SHAN Peng
2013, 28(2): 401-409.
Abstract PDF(1779KB) icon1923 icon1194
Abstract:
Low Reynolds number flow field developed around a cascade of NACA0012 was numerically simulated by directly solving the unsteady two-dimensional Navier-Stokes equations through weighted essentially non-oscillatory(WENO) schemes with 7th order accuracy.As compared with references,direct numerical simulation results indicate that vortex-shedding process at the cascade trailing edge is similar to that of flow over a cylinder and the statistical traits of the wake region are similar between cascade flow and single airfoil flow at low Reynolds number,but the former is stronger.The vortex-shedding has a significant impact on the overall flowfield,which forms unsteady separation on the airfoil and makes the total pressure in the wake region vary instantaneously.With the decrease of the pitch,the average separation position moves towards the leading edge;the frequency and amplitude of total pressure in the wake region increase markedly,and the statistics of pulse velocity becomes bigger.
Wave system analyses of four-port through-flow wave rotors
CHAN Shi-ning, LIU Huo-xing, HU Xiao-yu
2013, 28(2): 410-417.
Abstract PDF(998KB) icon1867 icon1358
Abstract:
Aiming at four-port through-flow wave rotors used in gas turbines,the pressure wave system inside the channels was simplified,and analytic models were established and proved with foreign experimental results.The analytic wave system models were finally used to analyze the relationships among boundary conditions,wave structures,wave rotor performances,and parameters of other components such as compressors,turbines or combustors.The results show that:the rise of high pressure air (HPA) static pressure could effectively increase the wave rotor pressure ratio,as a result of strengthened entire wave system;the wave rotor performances could be optimized by properly designing the compressors and turbines;the matching of wave rotors and combustors could restrict the combustor design,while the rise of combustor total pressure recovery could enhance the wave rotor compression efficiency.
Applying low-speed modeling method to high pressure turbine stage
WEI Wei, MA Hong-wei
2013, 28(2): 418-425.
Abstract PDF(1521KB) icon1802 icon1185
Abstract:
Based on the successful experience of applying low-speed modeling technology to high pressure compressor of aero-engine,the aerodynamic design method of turbine with similar technology was investigated,and an improved blade redesign method was illustrated.Referring to an adjusted similarity principle,a low-speed turbine research facility was established,which was aerodynamically and thermally represented by the first stage of prototype high pressure turbine of E3 core.In the design process,identical structural parameters between the prototype and the expected facility,such as solidity,span-to-chord ratio,and tip clearance-to-span ratio,were assured while similar aerodynamic performance was verified;besides,acceptable similarity of non-dimensional blade surface isentropic Mach number distribution was ascertained.Numerical simulation results shows that flow coefficient and blade surface pressure distribution are not suitable in the modeling of turbine for the distinction of total pressure and total temperature.According to the similarity parameters,the modeling shows a good correspondence in aerodynamic performance, proving that the low-speed facility will provide an appropriate test platform for aerothermodynamics research of turbine.
Experiment on single axial compressor of characteristic of rotating stall
LUO Zhi-huang, LI Jun, YANG Pu, WU Yun, LIU Dong-jian, LI Fan-yu
2013, 28(2): 426-431.
Abstract PDF(1363KB) icon2039 icon1295
Abstract:
The stall inception of a single low speed compressor was investigated with uniform inlet flow.By installing high response dynamic pressure transducers in the circumferential and axial directions,the dynamic pressure data at different positions were collected and analyzed using time analysis and frequency analysis,respectively.The results indicate that the spike-type inception will appear before stall;the stall cells are splited and incorporated,but two cells are always incorporated to one when exiting from stalling quickly;and frequency analysis of the dynamic pressure validate the veracity of the number of stall cell.
Torsional vibration characteristics analyzing and modeling for helicopter tail drive system
ZHU Zi-bing, ZHU Ru-peng, BAO He-yun
2013, 28(2): 432-438.
Abstract PDF(2365KB) icon1846 icon1069
Abstract:
The helicopter tail drive system was simplified to a series system with shaft section and equivalent disk.A equivalent dynamic analysis model with multiple degrees of freedom,in which the transmission error of meshing gear pair and meshing stiffness of tail-decelerated gear were included,was established for this simplified helicopter tail drive system.According to the torsional dynamics equation of helicopter tail drive system,the torsional vibration response of system was obtained, and the torsional vibration characteristics of the system with different torsional stiffness of the shaft and meshing stiffness of the gear were discussed. The following conclusions may be drawn from the analysis result. The torsional displacement of tail rotor is larger than the torsional displacement of driven gear of tail gearbox, namely the vibration response of output gear of tail gear box is larger than the input gear. The variation tendency is opposite of the torsional angle displacement between the equivalent disk connected to the horizontal shaft and oblique shaft respectively. The meshing stiffness has more influence on the system than the shaft torsional stiffness, it should be taken account into the modeling of helicopter tail drive system.
Research on oil-air multiphase flow of spray lubrication of aero spur gears
WANG Yan-zhong, NIU Wen-tao, TANG Wen, GUO Mei, GUO Xia, LI Guo-quan, SHEN Rong
2013, 28(2): 439-444.
Abstract PDF(786KB) icon1904 icon1321
Abstract:
Aiming at the transient flow state of the spray lubrication process to aero spur gears,the mesh process and lubrication state of aero spur gears with spray lubrication were firstly analyzed,and the math model of oil-air multiphase flow which was suitable for the spray lubrication of gears was established.Then the numerical model of the multiphase flow was established and the results were obtained,which included the oil-air ratio and the entrance pressure at every mesh point and their changes with the mesh process.The precies flow parameters and pressure boundary conditions to the elastohydrodynamic lubrication and mixed lubrication analysis of the aero spur gears are shown.
Natural characteristics and dynamic load coefficient of power four embranchments gear transmission
LI Nan, WANG San-min, DU Jia-jia
2013, 28(2): 445-451.
Abstract PDF(2007KB) icon1627 icon1044
Abstract:
Dynamic model of power four embranchments gear transmission system has been provided,and vibration equation of a single axis has also been established based on axis-element method. With the gear mashing matrix,coupling between equations of every axis can be achieved,which helped to establish dynamic equation of the whole power transmission system. Solving that equation,natural frequency and natural vibration of system were obtained,and the conclusion that the system needs damping design to make sure it work stably at the normal working speed has been conferred. Meanwhile,difference between dynamic load coefficients of different transmission errors has been analyzed,and results show that transmission error has an obvious effect on dynamic load coefficient of the power four embranchments gear transmission system.With the increase of the transmission error,the dynamic load coefficient is also increasing,especially in high speed stage gears the performance even more significant.The research methods and conclusions lay foundation for dynamic optimization design of power four embranchments gear transmission system.
An iterative approach for modal analysis of solid rocket motor incorporating frequency dependent modulus
Muhammad Adnan, SUN Bing, ZHANG Jian-wei, Sarosh Ali
2013, 28(2): 452-458.
Abstract PDF(892KB) icon1462 icon1003
Abstract:
The modulus of viscoelastic materials varies with excitation frequency.However,during modal analysis of frequency dependent materials,a material evaluation frequency is necessary because stiffness cannot be modified during eigenfrequency procedure.As a result,only those vibration modes are accurate,of which eigenfrequency is close to the material evaluation frequency.In order to obtain vibration modes of solid rocket motor (SRM) using material modulus based on frequency which is the same as the eigenfrequency,an iterative approach was proposed.Results of the iterative technique show that frequency modes obtained from the method are in complete agreement with the eigenfrequency and material evaluation frequency.
Numerical simulation of axial liquid film cooling in rocket combustor
YANG Wei, SUN Bing, ZHENG Li-ming
2013, 28(2): 459-465.
Abstract PDF(681KB) icon1405 icon1015
Abstract:
Numerical simulation has been done for liquid film cooling in liquid rocket combustor.Multiple species of axial Navier-Stokes equations have been solved for liquid-film/hot-gas flow field,and k-ε equations have been used for compressible turbulent flow.The results of the model agree well with the results of software FLUENT.The results show that:(1) Liquid film can decrease the wall heat flux and temperature effectively,and the cold border area formed by the film covers the whole combustor and nozzle wall.(2) The turbulent viscosity is higher than the physical viscosity, and its biggest value is in the border area of the convergent area in nozzle.The effect of turbulent flow on the whole simulation field can not be ignored.(3) The mass fraction of kerosene at the film inlet is 1,but it decreases along the nozzle wall and achieves its lowest value at the outlet.However,the mass fraction of kerosene near the wall is the biggest at any axial location.
Uncertain structural analysis of solid propellant grain and comparison of the methods
LIU Dong-qing, SUN Bing, ZHANG Jian-wei
2013, 28(2): 466-472.
Abstract PDF(576KB) icon1737 icon1097
Abstract:
Concerning the influence of uncertainty in composite solid propellant's mechanical properties on structural analysis of solid rocket motor(SRM) grain,the parameterized finite element model of SRM grain under temperature and pressure loading is constructed through ANSYS parametric design language (APDL).On that basis,the influence of random distribution of composite solid propellant's thermal expansion coefficient and initial Poisson's ratio on finite element structural analysis of SRM grain is studied with Monte-Carlo method and response surface method.Results of the two different methods are compared.The results show that small changes in composite solid propellant's thermal expansion coefficient and initial Poisson's ratio cause relatively great influence on the results of structural analysis and the structural responses of the propellant grain are more sensitive to initial Poisson's ratio.So,uncertainty in composite solid propellant's mechanical properties should be considered during finite element structural analysis of SRM grain.It is indicated by the comparison of this two kinds of methods that response surface method can give approximately the same results as those from Monte-Carlo method and is greatly more efficient than Monte-Carlo method.
Exhaust gas electrostatic monitoring and gas path fault feature for turbojet engine
LIU Peng-peng, ZUO Hong-fu, FU Yu, SUN Jian-zhong
2013, 28(2): 473-480.
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Abstract:
Some experimental stages of electrostatic monitoring explorative experiments which used the engine test bed and a certain small turbojet engine were conducted. The characteristics of electrostatic signal of the turbojet engine's exhaust gas were obtained, and the electrostatic monitoring technology's ability of monitoring the engine gas path mechanical faults was verified.Then,the result of the next research shows that electrostatic signal of the turbojet engine's exhaust gas may change a little with the engine conditions.There are some evidences obtained by the analysis of the electrostatic signal in stage 102 showing that the activity level changes with the engine conditions,and the activity level is a characteristic parameter of the charged micronized particles in the turbojet engine's exhaust gas.In the process of engine test from stage 102 to stage 108,there were some faults such as engine combustion chamber carbon deposition fault,mild ablation breakdown and lub oil leaking in gas path.There were some changes in electrostatic whole level of engine's exhaust gas which can be found by analyzing signal statistical and long time domain to make characteristic parameters of the electrostatic signal like active level and positive (negative) event rate as early-warning parameters corresponding with these faults.

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