2013 Vol. 28, No. 1

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Harmonic balance method for nonlinear vibration of dry friction oscillator with Iwan model
WANG Ben-li, ZHANG Xiang-meng, WEI Hong-tao
2013, 28(1): 1-9.
Abstract PDF(779KB) icon1864 icon1316
Abstract:
Free vibration as well as forced vibration of a dry friction oscillator which was composed of Iwan model and a mass were investigated by harmonic balance method (HBM).For free vibration,the nonlinear equations of the motion of the system in the processes of loading and unloading were presented respectively.Then,based on HBM,the first-order approximate harmonic solution of each equation was derived.A strategy was proposed to detect the moments of zero velocity so as to achieve the correct numerical solutions.The results of a numerical example show that the solutions of HBM coincide well with those of the numerical method,so the validity of the method for such problem is verified.For forced vibration accompanied with microslip,the amplitude-frequency relationship of the system was derived by HBM.Finally,the damping characteristics of the Iwan model were studied.It is seen that a nonlinear relationship exists between the equivalent viscous damping of the model and its displacement amplitude.
Compressive properties of homemade carbon fiber composite laminates with delamination defect
FU Hui-min, YANG Yu-song, ZHANG Yong-bo
2013, 28(1): 10-15.
Abstract PDF(886KB) icon1257 icon1118
Abstract:
Large numbers of aircraft composite structures were researched, and the distribution of delamination sizes and though thickness positions in the composite laminates were investigated. An experiment was conducted to probe into the effect of delamination sizes and through thickness positions on the compressive strengths of laminates with single embedded circular delamination with the most dangerous delamination sizes and positions defined from the distribution. A shell model was established for compressive strength prediction, and the virtual crack closure technique (VCCT) was employed for the strain energy release rate calculation. The finite element (FE) prediction was in good agreement with the experimental measurements, for the predicted compressive strengths stood within 10% error of experimental results. It was observed that the compressive strength was highly effected by the delamination size, while the though thickness position of delamination did not have significant effect on the compressive strength.
Vibration response analysis of gear coupled rotor system considering geometric eccentric effect of helical gears
MA Hui, WANG Qi-bin, HUANG Jing, ZHANG Yi-min
2013, 28(1): 16-24.
Abstract PDF(1409KB) icon6210 icon3785
Abstract:
Taking three-shaft parallel coupling rotor system with two pairs of helical gears as the research object,a meshing dynamic model with total degrees of freedom was established by considering the effects of the static transmission error and the geometric eccentricity of the gears.Combined with the rotor system,a finite element model of the multi-shaft helical gear rotor system was determined.In the model,the rotor system was simulated by using beam element and the gear pair was simulated by using mesh stiffness matrix and damping matrix.Finally,considering the static transmission error,rotor unbalance,gear geometric eccentricity and the coupling,dynamic characteristics of the system were analyzed.The results show that geometric eccentricity has a great effect on gear meshing force,of which the role is equivalent to a torque applied on the gear.
Effect of curvature attribute of free-form surface on CNC milling process
WANG Ming-hai, LI Xiao-peng
2013, 28(1): 25-31.
Abstract PDF(1205KB) icon1287 icon1330
Abstract:
A method was presented to analyze the computer-numerical-control (CNC) milling process based on characteristics of the curvature of curved surface. It applied differential geometry theory to CNC milling process. This method was employed to analyze the effects of the curvature attributes of isoparametric curves on the interference and cutting width during the process through planning the cutting path on the constructed free-form surface and establishing cutting path isoparametric curve. At the same time, according to the research on the relationship among the cutting path, the scallop height and the attributes of curvature of curve, some laws affecting the machining efficiency, accuracy and interference were obtained. In addition, the research shows that the cutting width can be improved effectively by optimizing the anastomosis curve of the cutting tool radius, the scallop height and machined surface's curvature. The experimental results show the effectiveness of the method in analyzing CNC milling process based on the attributes of the curvature of curves,the machining efficiency can be increased 5%~8%.
Distribution characteristic of durability load based on fixed task frequency mixing
ZHAO Fu-xing, LV Yu-ze, ZHENG Xiao-mei, YANG Xing-yu
2013, 28(1): 32-37.
Abstract PDF(473KB) icon1411 icon1039
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In order to evaluate operational reliability of structural components,distribution characteristic of durability load based on fixed task frequency mixing needed to be analyzed.Mathematical statistics method was used and cumulative progress of flight load was studied according to the central limiting theorem of the same distribution.Distribution function of cumulative load was deduced.It is proved that as the flight profile accumulates,distribution of durability load cumulant tends to be normal.Distribution characteristic algorithm of durability load was presented.The distribution characteristic of durability load cumulant was demonstrated by four examples of numerical simulation.Results show that relative variation coefficient decreases as the number of cumulated flight profiles increases.
Series solution of symmetric dry frictional stick-slip motion and stick-slip boundary characteristics
QIAN Da-shuai, LIU Zhan-sheng, WANG Le, XIE Liang
2013, 28(1): 38-45.
Abstract PDF(570KB) icon1474 icon1076
Abstract:
To study frictional vibration problems in areo-engine,piecewise expression of frictional force in symmetric stick-slip motion was presented.Analytical series solution of symmetric stick-slip motion with even stops was derived by using harmonic balance method.Stick-slip boundary function in parameter plane was derived based on the series solution.Stick-slip response contained only odd harmonic components and super-harmonic resonances existed at odd fractional frequency ratios.When frequency ratio was less than 0.4,the stick-slip boundary curve had the feature of concave-convex alternation and its local minimums located at the super-harmonic resonant frequencies.Increase in viscous damping reduced the non-sticking parameter range at most frequency ratio ranges except near super-harmonic resonant frequencies,where larger viscous damping led to larger non-sticking parameter range.
Rotor-stator rubbing positions identification of aero-engine based on wavelet packet analysis and support vector machine
YU Ming-yue, CHEN Guo, LI Cheng-gang, FENG Guo-quan, WANG De-you
2013, 28(1): 46-53.
Abstract PDF(1736KB) icon1478 icon1216
Abstract:
Rubbing faults of different radial rubbing positions by using the rotor experiment rig of aero-engine are simulated.An identification method based on wavelet packet analysis and support vector machine(SVM) was proposed.Firstly,the acceleration signals on the casing were collected.Secondly,the signals were decomposed by wavelet packet analysis,and the normalized energy features were extracted.Finally,the normalized energy characteristics were input into support vector machine to identify the different rubbing positions.By using an aero-engine rotor experiment rig,a large number of samples including different rubbing positions and different rubbing degrees were simulated, and the support vector machine was trained and tested by these samples.The results show that the new method combining the wavelet packet energy features and support vector machine can effectively identify the rotor-stator rubbing positions of aero-engine;in addition,only one sensor is required to reach the recognition rate of 98%.
A control method of novel electrical composite force loading system
ZHANG Dong-hui, BI Shu-sheng, YU Jing-jun, PEI Xu
2013, 28(1): 54-59.
Abstract PDF(721KB) icon1116 icon1149
Abstract:
Based on an introduction to the structure and working principle of composite force loading system,the relation between composite force and branch chain forces was deduced,and a mathematical model of one branch chain force loading system was established to analyze its stability.The simulation and experiment lead to a conclusion that damp and noise of force are main factors which have a serious effect on the stability and response speed.A new control algorithm was proposed,and the experimental results show that the algorithm improves the performance of the system significantly.The frequency of combined moment and axial force loading can reach 10Hz by using this control method.
Aerodynamic characteristic modeling of electrically controlled rotor and wind tunnel test verification
LU Yang, WANG Chao
2013, 28(1): 60-66.
Abstract PDF(903KB) icon1403 icon1081
Abstract:
Firstly,the unsteady aerodynamic model of the airfoil with trailing-edge flap was developed.Secondly,the finite state wake model of electrically controlled rotor(ECR) based on the Peters-He generalized dynamic wake theory was developed,in which the effect of the trailing-edge flap on the rotor aerodynamic environment was considered.Combined with the relationship among the blade flapping angle, the blade pitch and the deflection angle of the trailing-edge flap,the model of calculating the aerodynamic characteristics of ECR was established finally.Then,wind tunnel tests were conducted,in which the aerodynamic force,the blade pitch,the deflection angle of the trailing-edge flap and the blade flapping angle varying with different test statuses were measured.Theoretical results basically coincided with the experimental data, which verified the correction of the theoretical model. Conclusions are drawn as follows: with the fixed rotor speed, there is a linear relationship between blade pitch response and flap control; rotor thrust decreases with the increase of flap collective control, and actual aerodynamic efficiency of the flap decreases under large collective control; in forward flight, flap collective control can cause changes of blade cyclic pitch.
Six-component balance calibration technology for nozzle model testing facility
LUO Hua-yun, LAI Chuan-xing, WANG Yue-gui, YE Wei
2013, 28(1): 67-73.
Abstract PDF(716KB) icon2117 icon1789
Abstract:
The balance calibration technology was developed with the method that theoretical computation was associated with model test in order to improve precision and accuracy of static and dynamic calibrations of six-component force-measuring balance for nozzle internal flow model testing facility.The original data of static calibration were processed by the method in which once quantic was compared to thrice quantic and the experiential model was obtained on phases of balance installation and test.The repeatability test indicates that precision and accuracy of dynamic calibration can be enhanced greatly with perfect method for data processing.The credibility of balance performance and correctness of correcting test data including added-force and added-moment of force-measuring system with the nozzle pressure ratio (NPR) were validated by being compared to the results of dynamic calibration for four-component balance.The method of six-component force-measuring balance calibration offers references for other multi-component force-measuring system calibrations.
Engine model correction based on entropy criterion PSO
WANG Yong-hua, YANG Xin-yi, SU Min, LI Dong, WANG Xing-bo
2013, 28(1): 74-81.
Abstract PDF(1069KB) icon1234 icon1115
Abstract:
The difference of single component characteristics which is caused by manufacture and installation can make the performance discrepant.A new entropy criterion particle swarm optimization (PSO) has been presented to revise the engine model based on the trial run data.The new algorithm adjusted the speed of inertia weight and migrated the particles of part poor fitness at the same time based on entropy discrimination.The presented algorithm overcame the defect of the original algorithm.The simulation results indicate that the single engine model correction based on entropy criterion PSO is better than the correction based on influence coefficient matrix (ICM).It is verified that the maximum error of the performance parameter is under 1.5%,which means the single engine model and real engine match better.
Bipyramid Bump compression surface design and aerodynamic characteristics
WANG Long, ZHONG Yi-Cheng, WU Qing, YANG Ying-kai
2013, 28(1): 82-89.
Abstract PDF(1923KB) icon1978 icon1239
Abstract:
An inverse design numerical method was introduced to investigate the design technique of new bipyramid bump compression surface.The axisymmetric Euler equations with the discontinuities boundary condition were solved on dynamic mesh using computational domain partition method which calculated the second shock wave in order to avoid solving the shock location error by shock capture method.On this basis,a bipyramid Bump example combined with the flat plane was designed by the streamline tracking method introduced to generate Bump compression surface,and it was simulated by computational fluid dynamics in viscosity.The results show that:(1) the model maintains a strong boundary layer swept capacity in the flow field structure;(2) at Mach number 2.0 condition,the method adopted here can make the total pressure recovery coefficient of the Bump compression system increases 0.04 compared to the traditional Bump compression surface based on cone waverider design,also lays the foundation for improving the Bump inlet performance.
Dispersion model for incompressible turbulent flows
DONG He, GAO Ge, DI Ya-chao
2013, 28(1): 90-95.
Abstract PDF(567KB) icon1481 icon1132
Abstract:
The energy inversion phenomenon which widely exists in turbulent flows was analyzed. Its cause which was called dispersion effect in turbulent flows was revealed. On this basis, a modified Boussinesq hypothesis containing dispersion coefficient and a new kind of eddy viscosity model were presented. The dispersion coefficient had different forms when the modified Boussinesq hypothesis was coupled with different turbulence models. The condition and direction of energy transfer were also described. The credibility of the new model was verified in numerical simulation of wall boundary layer flow and back-facing step flow. The frictional resistance coefficient and the velocity profile for turbulent boundary layer were in good agreement with the experimental results; the reattachment length, the surface pressure coefficient on step-side wall and the turbulence intensity profile for backward-facing step flow were closer to the experimental results than the standard k-ε model. Results show that the introduction of dispersion term can improve the accuracy of the prediction significantly with very little expenses, so the model should be useful in engineering application.
Design methodology of axisymmetric variable geometry inlet
TENG Jian, YUAN Hua-cheng
2013, 28(1): 96-103.
Abstract PDF(1301KB) icon1365 icon1069
Abstract:
Cone cavity flow was investigated with computational fluid dynamics(CFD) method.The flow structure and total pressure distribution were compared with experimental data.Results indicate that numerical results are in accordance with experimental data and the CFD method is creditable.Cone cavities with different shapes under various inflow conditions were studied;the coupling characteristic of cone cavity flow was analyzed and the flow phenomena downstream the cavity which were affected by cone cavity was presented.A kind of axisymmetric variable geometry inlet with movable cone tip was designed and its aerodynamic performances were compared with that of the relevant fixed geometry inlets.Results show that by translating cone tip backward toward the centerbody of the inlet,the exterior compression waves can be modulated and mass flow rate is obtainable above 0.99 when inflow Mach number exceeds the design point.The variable geometry technique would lead to an evident increase of mass flow rate without changing the geometry of internal compression duct of inlet.
Component-level modeling technology for variable cycle engine
GOU Xue-zhong, ZHOU Wen-xiang, HUANG Jin-quan
2013, 28(1): 104-111.
Abstract PDF(1227KB) icon7701 icon4386
Abstract:
A steady and transient component-level mathematical model of a double bypass variable cycle engine (DBVCE) was constructed considering the effects of variable inlet guide vane and variable turbine nozzle area on component characteristics of compressor and turbine.Besides,the effects of the mode selector valve area on deputy bypass inlet air flow were also considered during the modeling process of DBVCE;two typical operation modes such as steady state and mode switching transient process were simulated.Results show that as the mode selector valve closes down,the surge margin of front fan block decreases obviously.When working in double bypass mode,the specific fuel consumption of DBVCE is lower,which is fit for subsonic cruise flight;otherwise,the specific thrust is higher in single bypass mode,which is fit for supersonic cruise flight.
Wind buffeting noise analysis and control for high-speed vehicle side-windows
WANG Ning, GU Zheng-qi, LIU Shui-chang, DONG Guang-ping, LIU Long-gui
2013, 28(1): 112-119.
Abstract PDF(1429KB) icon1619 icon1342
Abstract:
By using large eddy simulation,numerical simulation of wind buffeting noise in a car when opening different side-windows was conducted.The mechanism of wind buffeting noise of side-windows was revealed,and the reason that the sound pressure level in the driver's ears exhibited differences in different cases was discussed.The results show that the turbulence intensity and the energy dissipation are relatively weak near the rear windows.When opening a rear window,wind buffeting noise is the maximum;when opening two,the air derived effect can effectively reduce it.A corresponding suppression measure which involved installing a kind of disturbed flow device was proposed,and the effects of wind buffeting noise under different shapes of devices were discussed.The simulation results show that the square device is the most evident,and the maximum degradation is 15dB.
Flow and combustion characteristics of advanced vortex combustor with hydrogen fuel
DENG Yang-bo, SUN Hai-tao, WANG Yu-long, YAN Chun-ji
2013, 28(1): 120-128.
Abstract PDF(2269KB) icon1513 icon1154
Abstract:
To provide a valuable theory basis for the structure design of the advanced vortex combustor (AVC) of the turbine in integrated gasification combined cycle (IGCC),experiment and numerical simulation were conducted to study the flow characteristics of the AVC under cold flow condition.On this basis,the reasonable arrangement of fore-body and after-body in the AVC with hydrogen fuel was attained.Using 19-step chemical reaction mechanism,a numerical simulation was conducted to study the flow and combustion characteristics of AVC with hydrogen fuel.The results show that the combustion can be steadily maintained,and the temperature at the outlet can be controlled below 1950K with the equivalence ratio of hydrogen and air being kept at 0.65 without gas injected into the cavity between fore-body and after-body.At the same time,there are total pressure loss coefficient of 2.7665% and combustion efficiency of 99.54%.Contrasting to the AVC without gas injected into the cavity,the AVC with flow injected has more regular and steadier vortex configuration,higher combustion efficiency,higher total pressure loss coefficient,and uneven temperature distribution at the outlet.
Numerical simulation of mist/air cooling in a single slot jet impingement
TAN Xiao-ming, LI Ye-fang, ZHANG Jing-zhou
2013, 28(1): 129-135.
Abstract PDF(1044KB) icon1468 icon1171
Abstract:
Numerical simulation was carried out on the heat transfer characteristics in a mist/air impinging single slot jet. The effects of phase-changing heat transfer of the water droplets, the mist mass ratio in the air and the geometrical parameters of the slot jet were studied to reveal the enhancement of heat transfer. The simulated results show that adding liquid droplets in an air flow enhances the cooling effect drastically. 90% cooling enhancement at the stagnation point was achieved by injecting 5% of droplets with the heat flux of 8000W/m2. When the mist/air mass ratio increases from 1% to 5%, the heat transfer enhancement of the stagnation region is 32%. Proper jet width and impinging height are important parameters for cooling effect. In this study, the best impinging cooling effect was achieved with the impinging height to jet width ratio of 4.55 .
Flow characteristics inside counter-rotating disk cavity
CHEN Shu-xian, ZHANG Jing-zhou, TAN Xiao-ming, ZUO Yu-yu
2013, 28(1): 136-142.
Abstract PDF(1109KB) icon1649 icon1050
Abstract:
The flow inside a counter-rotating disk cavity was studied numerically,and the validity of numerical model and methodology was evaluated by comparing the results with the experimental data in the literature.The results show that the flow structure in the cavity between counter-rotating disks is complex and the disk angular velocity ratio has an important effect on it.The effects of rotation Reynolds number and disk angular velocity ratio on the pressure in the cavity and frictional moment number on the disk were also studied.The results indicate that the pressure decreases and the frictional moment increases with the increase of rotational Reynolds number,and the pressure is the largest when the frictional moment is also the largest with the counter-rotating disks at the same speeds compared with others at different speeds.
Large eddy simulation of inclined transverse jet with pulsation
SHI Wan-li, GE Ning
2013, 28(1): 143-150.
Abstract PDF(1713KB) icon1463 icon1144
Abstract:
To study the flow characteristics of film cooling of flat plates with pulsation,the large eddy simulation (LES) calculation method was adopted to simulate inclined cylindrical hole transverse jet at nominal blowing ratio of 1.0 and the numerical techniques of high order symmetric weighted essentially non-oscillatory (WENO)- Roe scheme,implicit Newtonian time advance,dynamic Smagorinsky sub-grid model and the preconditioned technology were involved.The working conditions of inclined tube transverse jet included steady and pulsed jet.Calculation results showed the hairpin vortex structure in transverse jet flow field.Research shows that the pulsation of the jet hole import changes jet exit coherent structure,which means the mixing process of jet and mainstream is changed.
Numerical simulation of gas-particle flow in hot gas injection thrust vector nozzle
LIU Hui, XING Yu-ming
2013, 28(1): 151-157.
Abstract PDF(1180KB) icon1339 icon1149
Abstract:
The gas-particle inner flowfield of gas injection thrust vector nozzle in solid rocket engine was simulated using Euler-Lagrangian method,and the effect of solid particle on thrust vector performance was studied.The Roe scheme and monotone upstream-centred schemes for conservation laws(MUSCL)method were used for secondary-order accuracy spatial discretization for gas phase,and the implicit scheme was employed for time marching.The stochastic trajectory model and two-way coupled with gas phase were employed for particle phase.The results indicate that the strength of bow shock is increased due to solid particles,but the thrust vector angle and thrust coefficient are decreased;thrust vector angle and thrust coefficient increase with the particle diameter increasing under the same mass fraction of particle condition;thrust vector angle and thrust coefficient decrease with the mass fraction of particle increasing under the same particle diameter condition.
Effect of structural changes of swirl nozzle on two phase flow
SHI Wei-dong, ZHANG Liang, CHEN Liang, HE Hai-yan, LIU Jiang-hai
2013, 28(1): 158-163.
Abstract PDF(845KB) icon1405 icon1143
Abstract:
Contraposing a swirl nozzle for aerodynamically dispersing superfine powder,the Reynolds stress model was used to simulate the strongly swirling,compressible and transonic gas flow inside and outside the nozzles with different inlet angles and exit-cone angles.Meanwhile,combined with discrete phase model,a further study was conducted on the tracks and concentration distribution of particles between 1μm and 10μm.The results show that it has little effect on the swirl strength and turbulence intensity when changing the inlet angle.However,the swirl strength changes significantly in the nozzles,when the exit-cone angle is changed.The critical diameter of particles which can escape from swirl nozzle decreases as the particle density or exit-cone angle goes up,or as the inlet angle decreases.In the rear of the swirl nozzle,in order to obtain a good uniformity of concentration distribution,particles need to diffuse through a distance of about 20 times of the diameter of the nozzle outlet.
Effect of double inclined slotted casing treatment on centrifugal compressor performance
TENG Jin-fang, ZHU Ming-min, QIANG Xiao-qing
2013, 28(1): 164-170.
Abstract PDF(754KB) icon1488 icon1192
Abstract:
Numerical investigations were conducted to study the effects of double inclined slotted casing treatment on a certain centrifugal compressor's performance.The numerical results show that appropriate inclined angle combination of casing treatment slots helps to organize the flow matching between inlet guide vane and rotor blades.The detailed analysis of the flow-filed in compressor with casing treatment indicates that configuration A has the best ability to expand stability margin.With the suction and re-organization of the tip leakage flow,high energy flow is re-injected into the adjacent flow channel which controls the development intent of leakage flow in the axial and circumferential directions and improves the blockage situation downstream of rotor passage.Thus,the compressor stability margin is substantially increased.
Subsonic compressor plane cascade experiment at low Reynolds number
LING Dai-jun, WANG Hui, MA Chang-you
2013, 28(1): 171-179.
Abstract PDF(1182KB) icon1408 icon1181
Abstract:
The characteristics of flow in wake area and on blade surface had been obtained by experiment and so was the coefficient changing rule in different Reynolds number conditions.The experimental results show that with the Reynolds number decreasing,great changes happen in wake area and to Mach number distribution on blade surface.At the same time,the loss coefficient of cascade increasing rapidly.At low Reynolds number,the turning Reynolds number of this profile is bigger with the inlet Mach number incresaing.The main reason for loss coefficient increasing and great changes in wake area is the flow separation on suction surface in very low Reynolds number condition.
Compact finite difference schemes on non-uniform meshes for computational aeroacoustics
CHEN Zhi-fu, WEN Gui-lin, WANG Yan-guang, WANG Ming
2013, 28(1): 180-187.
Abstract PDF(611KB) icon1310 icon2011
Abstract:
When the classic compact finite difference scheme was applied to practical problems using non-uniform meshes,the spurious numerical oscillations would be excited.A high accuracy of compact scheme was developed for this problem.The general expressions of the scheme's coefficients were derived through Taylor expansion analysis;then the numerical dispersion and dissipation were analyzed by using Fourier analysis method.For the case that the sixth-order tridiagonal compact scheme was applied to non-uniform meshes,the results are shown:the dispersion and dissipation values are closer to the exact solution with the increase of disturbance factor;the scheme is asymptotically stable when the disturbance factor is less than or equal to 0.213,otherwise it is the opposite;the results of numerical solution for one-dimensional convective wave and two-dimensional wave propagation agree well with the theoretical solution,which shows advantages in the simulation of non-uniform meshes for computational aeroacoustis.
Rotating stall mechanism of dual-stage contra-rotating compressor
LI Xiao-jun, GAO Li-min, XIE Jian, LIU Bo
2013, 28(1): 188-194.
Abstract PDF(1236KB) icon1471 icon1101
Abstract:
Based on steady numerical simulation of contra-rotating compressor in lab, a numerical investigation of the rotating stall mechanism of a contra-rotating axial flow compressor was conducted.The study shows that:(1) the rotating stall inception which appears near the stall point is “spike” type;(2) the tip clearance vortex in rotor 2 develops rapidly near the stall point and the passage is chocked,which cause the instability of the whole compressor;(3) the aerodynamic stability of compressor is determined by the development of tip clearance vortex in rotor 2 because of the high loading on the blades.
Analysis on dynamic characteristics of aero-engine rolling bearing/dual-rotor system
DENG Si-er, FU Jin-hui, WANG Yan-shuang, YANG Hai-sheng
2013, 28(1): 195-204.
Abstract PDF(1755KB) icon1434 icon1302
Abstract:
The dynamic model of dual-rotor coupling system which included rolling bearing dynamics and rotor dynamics was established.Fine integral method and predict-correct Adams-Bashforth-Moulton multi-step method were used to solve the nonlinear dynamic equations of dual-rotor system.Then the influences of bearing structural parameters on dynamic response of rotors were studied.The result shows:(1)the displacement of rotors can be decreased and the stability of rotors can be improved by reducing radical clearance of inter-shaft bearing,but the slide ratio of cage would increase when the radial clearance decreases,so the radial clearance should be selected properly;the slide ratio of cage would decrease and the displacement of rotors would increase when the rollers of inter-shaft bearing are reduced;(2)the displacement and stability of rotors can be optimized when the groove curvature radius coefficients of rings and radial clearance of supporting bearings are decreased,and the stability of rotor would be improved when the rolling elements of bearings are increased.
Analysis of leakage characteristics of finger seal based on system responses
ZHANG Yan-chao, LIU Kai, ZHOU Lian-jie, HU Hai-tao
2013, 28(1): 205-210.
Abstract PDF(834KB) icon1281 icon995
Abstract:
The current work obtained the seal rotor displacement excitation through studying the association rules of rotor speed,rotor unbalanced force and rotor runout based on dynamic working characteristics of finger seal.Then,a dynamic computational model of finger seal system was constructed.The leakage clearance computation method was researched according to the dynamic displacement response characteristics from the constructed model.Then the dynamic leakage calculation method was constructed and the leakage analysis work was conducted.The results preliminarily shows that dynamic displacement response changes with the rotor excitation time in every rotation period.The dynamic leakage clearance produced by dynamic displacement response also changes with the rotor excitation time.The results also indicate that leakage numerical size is affected by working conditions,installation conditions and the abrasion degree of finger boots.The method was validated by the computational example of a special engine and the comparison of calculating results and test data in references.The research work can provide valuable reference for dynamic performances design and study of finger seal.
Belt drive clutch control system of unmanned helicopter
ZHOU Yao-ming, MENG Zhi-jun, HE Wei, WU Zhe
2013, 28(1): 211-218.
Abstract PDF(1085KB) icon1378 icon1294
Abstract:
In light of belt drive clutch control requirements in unmanned modified process of one helicopter,a control system with security features was researched.By analyzing the belt drive clutch manipulation principles and control characteristics,the design requirements of control system were proposed,and then overall design was determined.Rotating speed feedback and intermittent engagement were adopted to realize clutch automatic engagement and avoid excessive decline of engine rotating speed (ERS).Landing signal was collected and hardware cancellation was adopted to avoid responsing dangerous instructions in flight.Rotating speed feedback and magnetor intermittent grounding were used to prevent engine overspeed.Automatic engagement experiment and overspeed experiment were conducted in an unmanned helicopter,and air/ground protection experiment was conducted through simulation.The results show that the minimum ERS is 960r/min in automatic engagement experiment;the maximum instantaneous ERS is 2016r/min;the minimum ERS is 1088r/min,and the overspeed duration is 0.5s in overspeed experiment;air/ground protection experiment confirms the function of instruction normal execution in ground state and instruction cancellation in air state.These experiments prove that the control system meets the needs of unmanned helicopter.
Design and experiment of two-stage flow control valve
LI Jun-hai, YU Nan-jia, CAI Guo-biao
2013, 28(1): 219-225.
Abstract PDF(1108KB) icon1497 icon1219
Abstract:
Principle and design methods of a new two-stage flow control valve were presented.Tank pressure was used to regulate the motion of the valve to open the valve and change the work status.The pressurization feeding system started and changed the mass flow rate of the oxide as the valve worked.The key parameters of the valve,including key part's outer diameter,the stiffness and initial compression of the spring,were analyzed.The tests show that the coefficients of local pressure loss of the valve were same at different working statuses.Experimental results for the feeding system using the valve were obtained.In the tests,the valve opened quickly and the feeding system changed the mass flow successfully.In the first stage,the mass flow rate of the hydrogen peroxide was 4.5kg/s.In the second stage,it was 2kg/s.It is proved that the design and test methods of the valve are feasible.
Analysis of oxidizer-rich preburner dynamic characteristics
LIU Shang, LIU Hong-jun, CHEN Hong-yu
2013, 28(1): 226-232.
Abstract PDF(1696KB) icon1384 icon1291
Abstract:
The linearized frequency models for oxidizer-rich preburner were developed to analyze the preburner pressure dynamic response under the propellant flow rate disturbance.The validity of the models and calculation method were confirmed by comparing the results with the test data from references.Using the adiabatic flow model which considered entropy wave during the low frequency range,the frequency responses of preburner pressure under kerosene and liquid oxygen flow rate disturbance were compared respectively,and the result shows that kerosene flow rate disturbance causes higher entropy wave amplitude.The influence rules of the dimensionless slope of combustion temperature and mixture rate as well as pressure ratio of the turbo and combustion time lag on the preburner frequency characteristics were also analyzed.When the concerned frequency range is wide,the distributed parameter model considering the acoustic effect should be used,because the model not only contains the adiabatic flow model during the low frequency range,but also can reflect the longitudinal acoustic oscillation.
Optimization design and robustness analysis of decentralized control for integrated flight/propulsion systems
DAI Ji-yang, HUANG Ying, PENG Chen
2013, 28(1): 233-240.
Abstract PDF(778KB) icon1545 icon1263
Abstract:
With an integrated flight/propulsion control system of a short take-off and landing fighter as design plant,an optimization design approach for decentralized control was proposed in order that it can maintain the performance and robustness of its corresponding centralized control.A centralized controller was firstly designed by using genetic algorithm as the performance reference for the decentralized controllers.The optimization design method for the decentralized controllers with interface variable was then provided.A critical element affecting decentralized control performance was analyzed and the decentralized control performance expression using frequency weighted matrix as design parameter was deduced.The problem of designing the decentralized controllers was converted into optimization problem solved by genetic algorithm.An improved balanced reduction method was also used in decentralized controller design.The simulation and structured singular value analysis show that the proposed optimization design method is so effective that the decentralized control system approximately reaches the same performance and robustness achieved by centralized control system.

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