1991 Vol. 6, No. 4

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1991, 6(4): 289-290.
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Abstract:
AEROELASTIC STABILITY ANALYSIS OF AERIAL PROPELLERS
Zhou Sheng
1991, 6(4): 291-294,373.
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At present,in respect of propellers of chinese commercial airplanes,stall flutter deserves extra attention.In our designing subsystem both empirical method and numerical simulation are employed for predicting the onset of stall flutter.In the empirical method,three nondimensional parameters at characteristic section of the propeller are used,i.e.reduced frequancy、inlet relative Mach number and incidence parameter.The numerical simulation is based on strip assumption.At the strip sections of a propeller,the transonic unsteady flow is considered to be induced by its oscillating blades.In calculation of aerodynamic damping,a simple engineering model is applied to considering the large scale region of flow separation at the blade suction surface.The results of numerical simulation for a new designed propeller are given.The variations of incidence and inlet relative Mach number at the characteristic section with aircraft flight velocity are shown in Fig.1 and 2.The dependence of the aerodynamic damping of the propeller on the incidence at the characteristic section in Fig.3 corresponds to the take off regime of the airplane.It is shown that there is no danger of the stall flutter onset in this case.The spanwise distribution of the incidence under the take off regime is also given in Fig.4.According to the whole flight envelope of the airplane,the greatest possibility of aeroelastic instability of the propeller corresponds to the ground static state of the airplane.At the ground static regime the incidence of the characteristic section is 9.96°.But the results of the numerical simulation show that there is no onset of the stall flutter in this case.This conclusion has been testified by the long term tests of the new designed propeller.
EFFICIENT LIFTING LINE METHOD FOR COMPUTING PERFORMANCE OF PROPELLER
Chen Zemin, Pan Jieyuan
1991, 6(4): 295-299,373.
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An efficient lifting line method has been developed for computing the performance of propeller.The present method features:1.The local gradient on the mean camber surface is used as a boundary condition instead of plane boundary condition so as to make the method applicable for propellers with large camber airfoil;2.A very good approximation of the velocities induced by semi infinite helical vortex lines is obtained by a combination of direct numerical integration of the exact integrand and exact analytical integration of its enveloped functions,so that the required computing time is reduced to only about 10% of the original one;3.The effects of blade section drag and compressibility have been considered in the computation of the propeller performance comparison of analytical and experimental results for a propeller are presented.It demonstrates the validity of the computational results,when the advance ratio is not too small.
AERODYNAMIC DESIGN OF PROPELLER BY NUMERICAL OPTIMIZATION
Pan Jieyuan, Qian Huede
1991, 6(4): 300-304,374.
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A numerical optimization method is presented for aerodynamic design of propeller.As the basis of optimization,the strip theory based on Goldstein theory is applied to prediction of the propeller aerodynamic performance.The comparison of calculated results with experimental data shows that,the strip theory is appropriate to the optimization.The mixed penalty function method is used for the optimization.By the means of the method presented here,two propellers have been designed and redesigned under identical flight conditions.The calculated results indicate that the variation of efficiency with geometry parameters is more gradual in the vicinity of efficiency maximum.It is also shown,if both chords and twists in different sections are taken as design variables,the blade of the optimized propeller would be more narrow than that if only the twists are taken as design variables.Therefore the optimized propeller would be lighter and more efficient at cruise conditions.
AERODYNAMIC MODIFICATION OF A PROPELLER
Zeng Ming, Gu Gaochi
1991, 6(4): 305-309,374.
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The aerodynamic design features of the propeller have been analysed at first.According to the analytical results and the modern advancements in propeller technology,the specifications of its expected modification have been proposed.In its overall design the important parameters have been determined.The principles of optimization and the version selection are outlined.From the comparison between the wind tunnel testing results of both scaled models of the propeller and its modification,it is concluded that the modification is a great success.Its static thrust and takeoff climb efficiency are increased by 13 8% and 8 76% respectively.Its cruise efficiency and noise level are also slightly improved.All they exceed the expected ones.
SURFACE FLOW VISUALIZATION OF ROTATING PROPELLER
Mao Xichang, Zeng Ming, Gao Chunfeng
1991, 6(4): 310-312,374.
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Surface flow visualization has been carried out with tufts adhered to the surfaces of the rotating propeller blades.From the experimental results it is found that in part of four fifths of blade surface from hub to tip,the air flow runs from leading edge to trailing edge in the outward direction with some inclination to chord.In the region of one fifth near the blade tip,flow separation and reverse flow occur at the blade surface,circulation appears even in the serious case,in consequence negative thrust emerges,which cuts down the efficiency of the propeller obviously.
NUMERICAL PREDICTION OF SOUND FIELD GENERATED BY PROPELLER
Zhou Sheng, Huang Lixi
1991, 6(4): 313-316,374-375.
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A fast and accurate numerical method is presented for predicting the sound field generated by subsonic propellers.The free space field,including the near and far sound field radiated by noncompact sources,is calculated by means of a retarded time integration in time domain.The FW H equation is applied to solving the sound field generated by moving boundaries of solid body in the flow field,but its quadrupole term is neglected,thus the noncompact sources mean the thickness source and the load source both included in the dipole term.According to the assumption,the sound field generated by a 3 D shaped propeller is considered as the sum of the terms radiated by each strip element located spanwise.The pressure chordwise distribution at each element should be known before solving the sound field.For this purpose a code solving 2 D compressible full velocity potential equation with body fitting coordinates is used which has been developed by BUAA previously.Comparison of calculated results with test data proves the present method and the code to be useful engineering tools.This conclusion has been also testified in the design of a propeller.
AEROACOUSTICAL MODIFICATION OF A PROPELLER
Li Xiaodong, Yang Xiaodong, Hu Zongan
1991, 6(4): 317-319,375.
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An aeroacoustical modification of a propeller is considered with the aim of great enhancement of its takeoff efficioncy and appropriate cutdown of its noise level when its blade number,blade hub and cruise efficiency are kept unchanged.A time domain method is applied to predicting near and far the sound field.From iterative aeroacoustical and aerodynamical optimization an optimum design scheme has been obtained.And two 1/3 scaled model propellers were made to simulate the original and modified propellers respectively.The results of comparative ground experiments show that the OASPL(Overall Sound Pressure Level)decreases by 1 to 1 5 dB while other technical spesifications are met.
EXPERIMENTAL CHARACTERISTICS COMPARISON BETWEEN TWO SCALE MODEL PROPELLERS
Mao Xichang, Wang Jiebing, Li Hongmin
1991, 6(4): 320-324,375.
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The aerodynamic and acoustic charaeteristics of two scale model propellers are compared experimentally.A three blades model(Model A)is a scale model of a production type.A four blades model(Model B)is a scale model of a new designed propeller.Their rotational speeds vary between 1500 to 3000rpm.Experimental results indicate that under identical operational conditions the four blades propeller has higher thrust coefficient but lower noise level than the three blades propeller and also has lower noise level at the same power coefficient.The four blades propeller,of course,is superior to the three blades one in the efficiency and overall performance.
STRESS ANALYSIS OF A PROPELLER BLADE
Xiong Changbing
1991, 6(4): 325-327,375.
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Three dimensional finite element method is applied to stress analysis of the original and the redesigned propeller blade taking the loads,such as centrifugal and dynamical loads.In respect of stress distribution,the airfoil of the redesigned propeller blade is more reasonable.Its stress distribution approaches to isostrength,and safety coefficient also meets the given specification.Therefore,the redesigned propeller blade is an quite advanced design.
STRESS ANALYSIS OF A PROPELLER HUB
Xiong Changbing
1991, 6(4): 328-330,375.
Abstract PDF(331KB) icon1603 icon426
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Three dimensional finite element method is applied to stress analysis of a propeller hub taking centrifugal load,aerodynamical moment and blade centrifugal tension load.Since its construction is complicated,loads are various and its stress distribution is hard to analyze,the elastic stress plus principle is employed for this purpose.The analytical results show that the blade centrifugal tension load is predominant and its construction has been optimized to a certain extent due to current improvements during long time of its service and modifications so the stress distributions of its parts are quite even and reasonable,moreover safety coefficients are large enough.
DIGITAL SIMULATION AND EXPERIMENTAL MODAL ANALYSIS OF DYNAMIC CHARACTERISTICS OF A PROPELLER HUB
Li Kedong, Du Binlao
1991, 6(4): 331-336,375-376.
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The finite element method with 8 nodes three dimensional isoparametric elements and subspace iteration is applied to digital simulation of dynamic characteristics of a propeller hub.The sizes of the stiffness matrices[K]and mass matrices[M]in the equations are very large.The natural frequencies of the first six orders and its corresponding modes of the hub have been obtained from the experimental modal analysis.By comparison the results of the experimental modal analysis and the digital simulation are of the same order.
EXPERIMENTAL MODAL ANALYSIS OF PROPELLER BLADES
Li Qihan, Chen Zhiying, Zhang Dalin
1991, 6(4): 337-341,376.
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The vibration characteristics of propeller blades have been investigated by using experimental modal analysis technique.The emphasis of the investigation is put on the effects of different joint conditions of blade root ends and mounting ways of blades on the nature frequencies and modes of propeller blade vibration.From the contrast analysis of the results it is concluded that in order to understand and analyze the dynamic characteristics of propeller blades precisely,the calculations and experiments of coupling dynamic characteristics of blade hub shaft of propeller assembly should be completed for simulating the joint and mounting conditions between propeller and engine practically.
VIBRATION CHARACTERISTIC ANALYSIS OF A PROPELLOR BLADE
Kong Ruilian, Wang Yanrong
1991, 6(4): 342-344,376.
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The subspace iteration method and Jacobi′s method are used to solve the eigenvalue problem for the vibration of a propeller blade,in which the superparametric quadratic thick shell element with eight nodes and forty degrees of freedom is used to govern the motion equation,considering the effects of shear transverse deformation on the accuracy.The frequencies and vibration modes calculated by the program written by authors are in quite good agreement with the experimental results,and they can be used to judge whether the resonance occurs in the operation of the propeller,considering the effects of aerodynamic force excitation only.
A METHOD OF RELIABILITY ANALYSIS FOR PROPELLER BLADES
Fu Huimin, Gao Zhentong
1991, 6(4): 345-348,376.
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A distribution function of two dimensional threshold is given for fatigue crack propagation.A two dimensional stress threshold interference model is set up.The model is applicable to the reliability analysis and design of infinite life for propeller blades or other structural members with initial defects and accident damage.The functional correlation between the reliability of no crack growth and the initial crack sizes is obtained from the model and the maximum permissible crack sizes can be determined according to a given reliability level.In consideration of the fact,that the longer the service time,the greater the probability of accident damage,the overhaul periods of propeller blades with high reliability are also given.
EFFECT OF ANTIICER ON PROPELLER PERFORMANCE
ZhangAikun
1991, 6(4): 349-351,376.
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Comparative experiments of a propeller with and without the antiicer have been completed in a wind tunnel.The analysis of the experimental data shows that the effect of the anticer depends on the advance ratio(J)and the blade angle(β).First,the antiicer has no effect on the performance of the propeller when the blade angle is big enough and the advance ratio is small(β=40°,J<0 5).Second,the efficiency of the propeller with antiicer increases when the blade angle is big enough and the J is moderate(β=40°,0 51 3)or at a smaller angle with a moderate ratio(β=27 5°,J>0 5).In fact,when aircraft is flying,its propeller is almost running at the third condition.When the airarft takes off(J=0 618,β=28 79°),the antiicer reduces the propeller efficiency by 1 5 percent,and by 3 percent when the plane cruises(J=1 6130,β=40 41°).
A SMALL FIVE-HOLE SPHERICAL PRESSURE PROBE FOR COMPRESSOR EXPERIMENTS
Yan Jiukun, Wu Changming
1991, 6(4): 352-354,378.
Abstract PDF(233KB) icon1621 icon474
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A small five hole spherical pressure probe instrumentation system is developed and applied to compressor interstage parameter measurement.This instrumentation system has two features:One is smallness of flow disturbance due to small dimensions of the probe head,the other is an advanced data processing method of this system which comprises perfect probe calibration and data processing procedure.The analysis of the test results demonstrates that its performance is stable,its accuracy and data repeatability of its measurements are quite well.This instrumentation system can be applied to verification of the design parameters.
AN INVESTIGATION ON LASER ATTENUATION THROUGH SOLID PROPELLANT FLAMES
Zhang Ping, Xu Rongfu
1991, 6(4): 355-358,377.
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Attenuation experiments are introduced with the emphasis on a YAG pulse laser system with wave length of 1 06μm.The experiments include two parts:first,the measurement of laser signal attenuation through the flames above the burning propellant strands in a strand burner in order to compare the relative attenuation characteristics of different propellants;second,the measurement of laser signal attenuation through exhaust plume of a scaling down single chamber dual thrust solid propellant rocket motor in its sustain period.The experiments demonstrate that an obvious difference in the relative attenuation(from 2.6% to 12.7%)exist among the various propellants(DB,PS,HTPB and CMDB propellant)at same measuring conditions;the Al content in propellant formulation is a major factor of the attenuation;and the attenuation of the scaling down motor plume(35.7%)is more severe than at of the propellant strand flame because of the longer path and the higher concentration of particles in the plume.
RESEARCH ON CRACK COMBUSTIONS OF PROPELLANT GRAINS
Li Lu, Pei Haitao
1991, 6(4): 359-363,377.
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On the basis of experimental study of crack combustion of both composite and double base grains a comprehensive static igniting model has been established,which considers heat convection,heat conduction,heat radiation,erosive burning effect and the influence of acoustic oscillation chamber.Two sets of partial differential governing equations have been derived.As a result of their numerical solution variations of many principal parameters have been obtained such as the flame spreading velocity,the pressure distribution,the temperature distribution and the hot gas velocity distribution.The essential behaviours of propellant crack combustion could be easly predicted.For example,the flame predicted spreading velocity is proved in quite good agreement with the experimental data.This model is possessed of extensive applicability not only for the double base propellant but also for the composite propellant.
OPTIMAL DESIGN OF COMBINED STRUCTURE OF NOZZLE CONIC SUPPORT AND CASE JOINT OF SOLID ROCKET MOTOR
Jiang Hua, He Zixin, Chen Ruxun
1991, 6(4): 364-368,377.
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The optimal design of the combined structure of nozzle conic support and case joint is completed by means of a mixed method of optimality criterion method and mathematic programming method.A valuable method and helpful conclusions are supplied for decreasing structural mass and optimizing shape of nozzle support.Calculation of practical examples shows that the multi conic support is better than single conic one especially a short shell near the flang is approximate to cylindrical shell which can decrease the stress peak efficiently.The thicknesses of the shells and the flange,the thickness and the width of the case joint are dereased magnificently,therefore the overal mass of the structure is cut down by 16.35%.
MIXTURE RATIO FAILURE DETECTION FOR LIQUID PROPELLANT ROCKET ENGINE
Feng Xin, Zhang Yulin, Chen Qizhi
1991, 6(4): 369-370,378.
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The mixtare ratio failure detection for liquid propellant rocket engine has been studied by means of Kalman filtering and statistical hypotheses testing.A computer simulation of a variable thrust rocket engine demostrates that the algorithm developed by authors can effectively detect mixture ratio deviation.The simulation also gives some significant results useful for the practical application and the further research of the algorithm.
APPLICATION OF COMPOUND LEANED BLADES TO CONTROLLING SECONDARY FLOW
Su Jiexian, Feng Guotai, Wang Zhongqi
1991, 6(4): 371-372,378.
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Mechanism of controlling secondary flow by using positive leaned blades or compound leaned blades is considered in this paper.The conclusion is that the positive leaned blades produce a converse radial pressure gradient at the hub.Under its action the low energy fluid in the blade surface boundary layer is migrated from hub to midspan,the blade to blade transverse pressure gradient is reduced,passage vortices is weakened and hence the secondary flow losses are decreased.A computation of the compound leaned blades applied to guide vanes in a small engine has been performed as an example.Its results show that by comparison with conventional blades,the degree of reaction and static pressure at the hub of the compound leaned blades are increased,the flow behavior near the hub of working blades is improved;the degree of reaction at the tip is reduced and therefore the leakage losses are cut down too.It is proved that the positive leaned or the compound leaned blades are applicable to controlling the spanwise pressure gradient,the stage reaction and the downstream effect of the secondary flow.

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