1994 Vol. 9, No. 4

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A CONDITION MONITORING AND FAULT DIAGNOSIS SYSTEM FOR CIVIL AEROENGINES
Zhang Jin
1994, 9(4): 339-343.
Abstract PDF(781KB) icon1871 icon449
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A new ground system EMD (Engine Monitoring and Diagnosis System) has been developed which has the capability of fault isolation with only the measurements of limited monitoring due to new developed diagnosis algorithms.The output information of a limited monitoring system,as ECMII or ADEPT is transferred into the EMD system as input data.Main functions of the EMD are engine health monitoring and sensor fault identification,engine gas path module and subsystem fault isolation,engine condition comprehensive evaluation,engine parameter prediction and take off exhaust gas temperature margin monitoring.For engine health monitoring,a series of threshold values are used to judge the engine condition for each flight.A quick looking algorithm and the judgement criteria are used to identify the sensor fault.An advanced diagnosis algorithm main factor model has been developed to solve a set of linear equations for engine gas path and to obtain the estimations △x of 28 component characteristic parameters and false diagnosis risk α on the condition of 4 known measuring parameter deviations.
AN ARTIFICIAL NEURAL NETWORK APPLIED TO AIRCRAFT GAS TURBINE DIAGNOSIS
Chen daguang, liu fusheng
1994, 9(4): 344-348.
Abstract PDF(154KB) icon2120 icon512
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An artificial neural network based expert system has been developed and is applied to aircraft turbofan engine fault diagnosis.The case study of a high bypass ratio turbofan engine has verified the feasibility of a three-layer back propagation network.The very encouraging diagnostic results prove that the fuzzy association feature, the distributed memorizing and parallel processing ability,and the random error depressing capability make it an effective and quick method which has a very bright perspective and can be used extensively for aircraft engine diagnosis.
A MULTI-OPERATING POINTS GPA METHOD FOR ENGINE FAULT DIAGNOSIS
Chen Daguang, Han Fengxue, Tang Genglin
1994, 9(4): 349-352,440.
Abstract PDF(905KB) icon2128 icon571
Abstract:
The feasibility of the multi-operating points gas path analysis (GPA) for engine fault diagnosis has been analyzed.The averaged error of estimation J is an effective criterion for determining the diagnosis accuracy.The recommended value of J has been given according to the numerical tests.It has been analyzed how the number of the operating points and the selection of the monitoring parameters affect the effectiveness of diagnosis.It is shown that the number of the necessary operating points can be significantly reduced and the diagnosis accuracy can be enhanced as the mointoring parameters are increased properly and selected correctly.Supplemental measurement of the pressure behind high pressure compressor and the pressure between high and low pressure turbines is a practicable measure for improving the diagnosis accuracy.
IMPACT OF VARIABLE GEOMETRY ADJUSTMENT ON TURBOFAN ENGINE PERFORMANCE
Zhu Zhili, Zhang Jing
1994, 9(4): 353-356,440.
Abstract PDF(1380KB) icon1738 icon431
Abstract:
The impact of variable geometry adjustment on performance of military turbofan engine with afterburner is analyzed and discussed.The results show as follows:During supersonic flight,increasing the nozzle throat area is an effective way to increase thrust of engine,and the higher the flight Mach number,the more remarkable the effectiveness;the nozzle throat area enlargement results in raising the surge margin of the fan effectively;the bypass ratio can be controlled by adjusting the ratio of inner and outer areas at mixer inlet,and enlarging inner area improves the performance of the engine with afterburner,but narrows the surge margin of the fan.The operating point of the fan will be optimized when the nozzle throat area and the area ratio of mixer inlet are regulated jointly and coordinately.It will be of benefit to the engine performance improvement that the pressure ratio of the fan and the mass flow increase simultaneously,while the efficiency and the surge margin of fan are kept up at a high level.
A REAL-TIME SIMULATION MODEL OF A TWIN-SPOOL TURBOJET ENGINE
Liu Yan, Liu Wei, Chen Fuqun, Sun Bin
1994, 9(4): 357-360,440.
Abstract PDF(787KB) icon1981 icon431
Abstract:
A mathematical model for real time simulation of twin spool turbojet engine has been established,which comprises a linearized compressor characteristics model,simplified turbine characteristics and the dimension reducing method of non linear equation set.Under the identical regime and inlet flow conditions,the performance of the twin spool turbojet engine was simulated respectively by real time model and non real time model.The results of the simulations were compared with test data.Favorable results of the comparison give the validation of the fundamental hypothesis of this study.This model makes a very good compromise between computation speed and accuracy,and has good convergence.
TRANSIENT PERFORMANCE SIMULATION OF A LARGE LIQUID ROCKET ENGINE UNDER FAULT CONDITIONS
Wu Jianjun, Zhang Yulin, Chen Qizhi
1994, 9(4): 361-365,441.
Abstract PDF(509KB) icon2058 icon477
Abstract:
A non linear dynamic mathematical model for a large liquid rocket engine has been established,which comprises normal models and fault models based on large liquid rocket engine with turbo pump system.The transient performance simulation has been performed under fault conditions according to jump input of various fault modes such as main valve fault,pipeline leakage,pipeline blockage,pump efficiency losses,turbine efficiency losses,which have occurred in previous hot fire tests or will be possible to occur in future.Adaptive Runge-Kutta method is employed to simulate.The calculated results show that the established model is accurate and reasonable.The numerical method can simulate effectively the transient performance of the faults.Simulation results are also discussed and analysed in detail.The work lays the foundation for further study on choice of fault modes,fault detection and diagnosis based on the model.
SIMILARITY ANALYSIS AND NUMERICAL SOLUTION OF N-S EQUATIONS FOR LAMINAR FLOW IN A ROTOR-STATOR SYSTEM
Feng Qing, Zhou Bin, Liu Songling
1994, 9(4): 366-370,441.
Abstract PDF(1049KB) icon1975 icon404
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The similarity analysis for the N S equations and the boundary conditions of a rotor stator system has been completed which shows that the flow field is depedent on five parameters such as inlet flow coefficient,rotational Renolds number,gap ratio,shroud clearance ratio and inlet diameter ratio.The numerical results for the laminar flow field in the system with an axial inflow and a radial outflow have been obtained by the SIMPLE method.It is shown that the gap ratio and the shroud have a great effect on the existence of the rotational core;and the core tends to take form and increase its rotational speed with decreasing the flow coefficient or with increasing the rotational Renolds number.For the closed rotor stator system the results are in good agreement with earlier work done by the other authors.Both the similarity analysis and numerical computation have testified the conclusion that the radial velocity is dominated by inertial terms and the tangential one is dominated by both inertial and viscous terms.The minimum of the flow coefficient required to prevent the ingress of gas into the rotor stator cavity has been calculated,and its linear relation with the rotational Renolds number has been found,which is consistent with the published experimental data very well.
PERTURBATION TECHNIQUE FOR RELIABILITY ANALYSIS OF A ROTATING DISK WITH UNCERTAIN GEOMETRY
Wang Zhenying, Lü Wenlin
1994, 9(4): 371-374,442.
Abstract PDF(310KB) icon1947 icon477
Abstract:
Design methods for the aerospace technology are,in general,based on deterministic parameters.In paractice there always exist random deviations of parameters,such as material properties and geometry,forces,and boundary conditions.In most situations the random deviations are small,but their overall effect can have a strong impact on behaviours of critical components,particularly in failure and reliablility analysis.For this reason a probabilistic finite element method based on second order perturbation technique is used to analyze the reliabilty and the random stresses of a rotating disk with uncertain geometery,the elementary perturbation approach to this problem has been studied and formulas for the random stress and the reliability have been deduced.The effect of uncertain geometery on the reliability is considered by a simple numerical example.The accuracy and efficiency of the method is demonstrated by its application to a rotating disk with uncertain geometery.The reliability calculated by this method compares favorably with that obtained from Monte Carlo simulation.
STRESS ANALYSIS OF CHECK RING CONNECTING STRUCTURE BETWEEN COMPOSITE CASE AND NOZZLE
Cheng Xiaomin, Chen Ruxun, Yang Weiguo
1994, 9(4): 375-378,442.
Abstract PDF(310KB) icon2056 icon398
Abstract:
The check ring connecting structure between composite case of solid propellant rocket motor and conic fixed body of a nozzle is of great advantage to decrease the mass and stress.In order to analyze this structure an equivalent orthotropic axi symmetric body is used to represent composite motor case and a FEM program for contact problem with large deformations is developed.The calculation shows that the relative displacement between check ring and nozzle conic fixed body and the angle between two sealing surfaces are very small under the working load.This fact indicates that the check ring connecting structure is safe in application.The relations of the concerned structure parameters to the deflection of the sealing surfaces are discussed.For the sake of comparison it is also found that the structure of submerged fitting increases the contact area magnificently and decrease the angle between two sealing surfaces to 4.02%.
PREDICTION OF GEAR BENDING FATIGUE STRENGTH RELIABILITY
Le Xiaobin, Luo Lifong, Chen Ying
1994, 9(4): 379-382,442.
Abstract PDF(1445KB) icon1555 icon401
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A new viewpoint is taken that the fatigue failure of the gear under bending load is treated as a random event,and a method for predicting the gear fatigue strength reliability under bending load is obtained from researching the event.Two new random variables Kw and Dw are proposed to describe the random event of bending fatigue failure of the gear. Kw is the fatigue damage strength which indicates the inherent ability of the gear to resist the fatigue damage under bending load. D w is the overall fatigue damage quantity which indicates the fatigue damage degree of the gear under bending load in the life span.A cumulative fatigue damage probabilistic model of the gear fatigue strength estimation under bending load is established by means of Kw and Dw .Basd on the model,a predicting method is provided for the gear bending fatigue reliability.
EXPERIMENTAL INVESTIGATION ON CONVECTIVE BURNING IN A BED OF GRANULAR PROPELLANT BED
Yang Tao, Jin Zhiming
1994, 9(4): 383-386,443.
Abstract PDF(770KB) icon2119 icon403
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A semi closed bomb with 100MPa pressure limits was designed to investigate the ignition transient,flame spreading,and pressure wave propagation in a packed bed of granular propellant charge.The influences of parameters such as propellant properties,porosity,and blow out diaphragm thickness on the convective burning characteristics were examined.The 1-D pressure wave propagation was observed in the experiment.The dynamic impaction of the bed exists during the flame spreading process,which is a main factor to cause the pressure wave.The 1-D combustion wave can not be formed in the bed with low loading density.
EXPERIMENTAL INVESTIGATION ON FULL COVERAGE DISCRETE HOLE FILM COOLING
Wu Weiming, Zhang Qingfan, Li yafeng
1994, 9(4): 387-390,443.
Abstract PDF(300KB) icon1980 icon396
Abstract:
A heat shield with full coverage discrete hole film cooling has practical application in some afterburners.Effects of geometric parameters and flow parameters of the heat shield on effectiveness of film cooling were investigated experimentally.A convective heat transfer coefficient of the film cooling was defined as hg=qc/(Tg-Tw) ,where q c is heat flux obtained by solving heat balance equation for the tested plate with discrete holes,and Tg and Tw are gas temperature and tested plate wall temperature,respectively.A semiempirical expression for calculating heat transfer coefficient is provided for a given diameter of the discrete holes and their distribution.It might be useful to calculating heat shield temperature.
MULTIHOLE COOLING TECHNOLOGY ANALYSES
Meng Xiangtai, Liu Gaoen
1994, 9(4): 391-393,443.
Abstract PDF(331KB) icon1685 icon484
Abstract:
This paper is to analyse the advantage of the multihole cooling technology.The calculation showed that the combuster liner temperature with multihole cooling technology would be 150K to 200K less than the wall temperature with film cooling technology,and the term of inner convection within the multihole is the main factor to make the wall temperature being lower.
APPLICATION OF DIACTUATOR DISC THEORY TO AERODYNAMIC COMPUTATION OF AXIAL-FLOW FAN WITH SKEWED-SWEPT ROTOR BLADES
Zhong Fangyuan, Wang Jianming, Cai Na, Li Zhong
1994, 9(4): 394-398,444.
Abstract PDF(1321KB) icon1997 icon431
Abstract:
In order to spread the advanced technotogy of aeropropfan,skewed swept rotor blades are applied to axial flow fan and compressor.The diactuartor disc theory model is adopted to calculate the main flow of the skewed swept rotor blades in such a manner,as all blades forces affect on the first actuator disc,but the radial forces of blades vanish abruptly on the second actuator disc.Then the radial distribution of the boundary layer thickness (wake thickness) on the outlet surface of the rotor blade is taken as aerodynamic and aeroacoustic characteristic vectors.The effects of the secondary flow,endwall boundary layer,blades rotation and skewed swept regularity (mainly radial forces of blades) are corrected according to plane cascade testing statistical curves.In addition,the results of four calculations demonstrate the effects of the second actuator disc,radial force and corrected outlet flow angle on magnitudes of the calculation results separately.The aerodynamic and acoustic tests show a good agreement of the calculation results with test data.
PROPELLER PERFORMANCE PREDICTION WITH FREE WAKE ANALYSIS METHOD
Chen Zemin, Pan Jieyuan
1994, 9(4): 399-401,444.
Abstract PDF(260KB) icon1689 icon483
Abstract:
The calculations of propeller performance at different advance ratios have been eompleted with the free wake analysis method.The wake is divided into near and far regions.In the case of heavy load when the advance ratio of propeller is small,the contraction of wake has large effect on the performance of the propeller.The free wake analysis method takes the wake contraction into account.According to lifting lines for the blade loading distribution,propeller performance calculated shows a good agreement with experimental data.
HIGH-SPEED CAMERA MEASUREMENT OF A GAS-SOLID TWO-PHASE FLOW IN AN AXIAL-FLOW FAN
Wang Yunliang, Xu Zhong, Miao Yongmiao
1994, 9(4): 402-404,444.
Abstract PDF(312KB) icon1836 icon407
Abstract:
A high speed camera is used to measure the motion characteristics of particles in an axial flow fan.In the experiment the measurements of the motion characteristics of the particles are carried out on three circular surfaces.The employed particles are 1mm diameter foamed plastic spheres.From photo processing some valuable conclusions are drawn as following:(1)In the impeller channel,the concentration of the particles nearby the pressure side is higher,while the suction side is lower.And there is an area where no particle exists.(2)The trajectories of the particles approach to straight lines.Some particles collide with the pressure side and rebound from it,and the rebound angle is less than the impact angle.(3)The velocities of the particles on the pressure side is lower,while those on the suction side is higher relatively.
AN EXPERIMENT ON AEROELASTIC STABILITY OF A HINGELESS ROTOR MODEL IN HOVER
Xia Pinqi, Xu Guiqi
1994, 9(4): 405-408,445.
Abstract PDF(3465KB) icon1787 icon508
Abstract:
A 2 m diameter,soft inplane or stiff inplane,isolated hingeless rotor model in hover has been tested to investigate its aeroelastic stability.The hingeless rotor blade is constructed with flap lag torsion coupling.The investigation aims at effects of structural and dynamic parameters,such as the collective pitch,precone,sweep,blade lag frequency and rotor rotational speed on the aeroelastic stability.A new and simple technique is applied to the tests so that the excitation of cyclic pitch is accomplished at the blade lag regressing frequency in vertical direction.The experiment shows that the aeroelastic stability of the hingeless rotor blade in hover is slightly influenced by the rotor rotational speed and the blade sweep,but strongly influenced by the collective pitch,precone and blade lag frequency.
A NEW INDEX FOR EVALUATING EFFECTS OF CIRCUMFERENTIAL GROOVED CASING TREATMENT ON EXTENDING STABILITY
Du Zhaohui, Liu Zhiwei
1994, 9(4): 409-412,445.
Abstract PDF(922KB) icon1673 icon411
Abstract:
Based on the analysis of structural features of the circumferential grooved casing treatment,3-D incompressible,steady,time averaged N-S equation,continuity and k-ε two equation turbulance model equations are successfully applied to the flowfield calculation in the cascade with the circumferential grooved casing treatment.The flux of the gas through the treatment groove is proposed as a new index which can quantitatively evaluate the effectiveness and the capability of extending stability by circumferential grooved casing treatment.The effects of structural parameters and treatment positions on the effectiveness of extending stability are analysed and discussed.The conclusions are proved by a great deal of testing results.The method and technique can be applied to analysis and design of the casing treatments in a compressor.
EXPERIMENTAL STUDY ON BLADE POSITIVE CURVING IN TURBINE CASCADE WITH TURNING ANGLE
Tan Chunqing, Wang Zhongqi, Han Wanjin
1994, 9(4): 413-415,446.
Abstract PDF(253KB) icon1661 icon405
Abstract:
As contrasted with the experimental study on blade negative curving in turbine cascade with large turning angle,an experimental study of blade positive curving was also carried out under identical conditions.The experimental results show that blade positive curving intensifies the leading edge vortex and the passage vortex in comparison with conventional straight cascade,and increases the bubble separation loss of the leading edge vortex and the viscous dissipation loss of the passage vortex.As a result,the flux capability of the cascade is cut down by 8.8%,the mass flux averaged overall loss coefficient increases by 11.4%,at the same time the outlet conditions of the cascade further deteriorate.
DAMAGE TOLERANCE ANALYSIS OF EXPERIMENTAL DISK WITH CRACKS IN SLOTBASE
Chen Guanghao, Wang Rongqiao, Hong Qilin
1994, 9(4): 416-418,446.
Abstract PDF(245KB) icon1754 icon458
Abstract:
The damage tolerance of an experimental disk is analyzed in the light of fracture mechanics.The relation of crack tip parameter and crack length, a ,is determined by combination of the FEM and the J-integral method.The critical crack size ac is obtained based on the material toughness KIC .Then the crack propagation life of the disk is determined.The calculated results are consistent with the experimental data.Therefore,the present method as well as the computer program can be used for strength evaluation of a turbine disk.
MONITORING PARAMETER PREDICTION AND FAULT IDENTIFICATION
Chen Zhiying, Li Qihan
1994, 9(4): 419-421,446.
Abstract PDF(1565KB) icon1687 icon473
Abstract:
The time series analysis method is applied to condition monitoring and fault diagnosis of aero engine.The trending values of monitoring parameters can be predicted by building and estimating auto regressive model.Then the time series analysis and the mode identification technique are combined and through determining classification function and conducting correlation analysis among the parameters,some typical faults of the engine can be identified.
MODIFICATION OF STATOR IN AN AXIAL FLOW COMPRESSOR-STAGE
Cao Renjing, Tao Deping
1994, 9(4): 422-424,447.
Abstract PDF(246KB) icon1641 icon492
Abstract:
According to the detail analysis of the experimental results for the stator of an axial flow stage,the main factors of the stator losses have been found.The end treatment technique-hub swept technique,which can enhance the efficiency in stator hub under high blade loading,has been used in the modification.The redesigning scheme for the stator and its end treatment are presented,and the detailed through flow calculation and blade profiling have been carried out.Optimization of stator parameters has been made in the modification.The results of the modification show that the end treatment technique and blade profiling help improve the efficiency in end wall region.
NUMERICAL SIMULATION OF WAVES CONSTRUCTION IN TRANSONIC NOZZLE FLOW
Jiang Xinghong, Wu Xingping, Chen Fulian
1994, 9(4): 425-427,447.
Abstract PDF(266KB) icon1813 icon481
Abstract:
The Split-Coefficient Matrix (SCM) method is manipulated here for the numerical computation of Euler equations so as to simulate the two dimensional axisymmetric transonic nozzle flow.The coefficient matrix is splitted directly by a set of simplified formula.A second order accurate explicit scheme is constructed to compute inner grid points.The scheme is free of artificial viscosity and is economical in terms of computer memory.5151 grid points are embedded into the nozzle flowfield and the computational results are in good agreement with experiments.Once the flowfield is known,the Mach waves characteristic relations are numerically solved by Euler method.Based on the graphic output of the Mach number and Mach waves in nozzle,it is possible to demonstrate not only the formation and reflection of an oblique shock within a tested nozzle geometry but also its peculiar zonal distribution of expansion and compression waves.As a result excellent consistency between parameter distribution and waves construction is revealed.
NUMERICAL SIMULATION OF FLOW AND TEMPERATURE FIELDS IN DOUBLE CONVERGENT NOZZLES
Xia Chunlin, Liu Dezhang
1994, 9(4): 428-430,447.
Abstract PDF(296KB) icon2437 icon486
Abstract:
A numerical simulation was employed to study the flow and temperatare fields of hot exhaust gas mixing with cold air in exhaust ejector.In the calculation the algebraic stress model (ASM) with the effect of buoyancy forces as turbulence model was adopted.Four heat radiation flux model was taken as heat radiation model.Due to complicated geometry of the nozzles the boundary fitted curvilinear coordinates were employed and curvilinear mesh was generated with the help of TTM method,then the blocks were put together under the given boundary conditions.A new general numerical method is developed on the basis of SIMPLE (Sami-Implicit Method for Pressure Linked Equations),and a general software was compiled in the boundary fitted curvilinear coordinate system.This software can be used widely for numerical simulation of flow fluid,heat and mass transfer,combustion,radiation in mixed flow with arbitrary boundary shapes.The results for some aeroplanes illustrate that the double convergent walls of the nozzles can intensify the mixing of hot and cold flows,and the violent mixing can greatly reduce the heat radiation flux and the temperature of aeroengine exhaust gas in double convergent nozzles.
EXPERIMENTAL STUDY ON ATOMIZATION PERFORMANCE OF COAXIAL INJECTORS AT BACK VESSEL PRESSURE
Wu Jinxiang, Liu Weidong, Zhou Mong, Wang Zhenguo, Zhuang Fengchen
1994, 9(4): 431-434,448.
Abstract PDF(295KB) icon1955 icon504
Abstract:
A MF Laser Scatter Sizer and an experimental system designed by the authors were employed to measure the sprays produced by coaxial injectors of LOx/LH2 liquid rocket engines at back pressure in the vessel.Experimental results show that injectors work as both airblast and pressure nozzles;keeping the air/liquid mass flux ratio (ALR) constant,the atomization performance is improved when the air pressure drop (△Pg) is increased; and enhanced back pressure results in bad atomization of the liquid.Experimental correlations between spray mean size SMDand its main influential parameters have been obtained by fitting experimental data.Several injectors with different configurations have been investigated and the results obtained from the experiments provide valuable reference for injector design.
APPLICATION OF DETECTION FILTER TO SENSOR FAULT DETECTION AND ISOLATION
Du Kuanwen, Zhang Hongyue, Wang Yulin
1994, 9(4): 435-438,448.
Abstract PDF(288KB) icon1643 icon473
Abstract:
Detection filter,which is actually a specific class of observers,can fix the output error direction of the system,so that it can be associated with a particular failure mode and its known design failure direction.The detection filter algorithm developed by White & Speyer is applied to a sensor fault detection and isolation system in an aeroengine control system.A nonlinear engine computer simulation model is set up and used to process the close loop simulation which includes sensor fault detection and isolation system.An isolation method is presented to isolate the fault sensor location.The results of the simulation show that the present fault detection and isolation system is very effective.

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