2004 Vol. 19, No. 2

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Display Method:
Best Linaer Unbiased Estimate Method for Incomplete Data
FU Hui-min, WANG Hua-sheng
2004, 19(2): 169-173.
Abstract PDF(687KB) icon1683 icon494
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There are lots of incomplete data in the real engineering world. The joint probability density function of rank statistics for incomplete data is presented, and the formulas of means, variances and covariances of order statistics for incomplete data are established in this paper. Then the best linear unbiased estimate method for incomplete data is presented. The incomplete information among test data can fully be exploited and applied by the method, and the precision is improved in the statistical analysis of incomplete data.
Influence of Control Parameters on Dynamic Characteristics of Active Magnetic Bearing System
XIE Zhen-yu, XU Long-xiang, LI Ying, QIU Da-mou, YU Lie
2004, 19(2): 174-178.
Abstract PDF(686KB) icon1921 icon450
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Dynamic characteristics of turbine expender supported by magnetic bearings are studied in this paper.The relationships among innate frequency,stiffness and damping,and control parameters are discussed.It has been found that adjustment of control parameters has less influence on the first bending critical speed.On the other hand,little damping by control parameters will cause collision easily between the rotor and bearings.
Study of the Nonlinear Behavior of a Rotor-Bearing System with Rub-Impact
LI Zhen-ping, ZHANG Jin-huan, JIN Zhi-hao, WEN Bang-chun
2004, 19(2): 179-183.
Abstract PDF(752KB) icon1790 icon458
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With a view to observe the complexity nonlinear phenomena of a rotor-bearing system with rub-impact,the multi-initial condition bifurcation analysis method was used in the study.And more abundant nonlinear phenomena were found than that of the single initial point integration method by the numerical simulation of the rub-impact rotor-bearing system in definite parameters.It was shown that multiple attractors coexisted in a range of parameters.Meanwhile the solution variation was also studied,which effectively explained the complex nonlinear phenomena of the rotor-bearing systems.
Influence of Variable Thermophysical Properties and Thermal Radiation on Convection Heat Transfer in Transpiration Cooling
JIANG Pei-xue, YU Lei, REN Ze-pei
2004, 19(2): 184-190.
Abstract PDF(1055KB) icon2119 icon467
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The two-layer k-ε model was used to calculate the turbulent flow and heat transfer characteristics in a rectangular channel with transpiration cooling.The calculated results showed that increasing cooling flow rate greatly reduced the wall temperature,the local convection heat transfer coefficient and the temperature gradient in the main flow near the transpiration cooling wall.The changes of the ratio of St/St0for various values of the modified blowing ratioSt/St0for variable thermophysical properties with consideration of thermal radiation were less than the changes for constant properties.Increases of the main flow temperature increased the effect of the variable properties and thermal radiation.The influence of thermal radiation on the wall temperature was stronger than the influence of variable thermophysical properties.The influence of the variable properties and thermal radiation on the convection heat transfer coefficient was small.When the main flow temperature was high （e.g.2500 K） and the wall temperature was low （e.g.800 K）,the effect of the thermal radiation was not strong and the transpiration cooling effect was still obvious.
Nucleation Boiling Characteristics of Liquid in Wedged Gaps
TIAN Yong, XU Han, PENG Xiao-feng, WANG Bu-xuan, Lee Duu-jong
2004, 19(2): 191-195.
Abstract PDF(304KB) icon1852 icon443
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An experimental investigation was conducted to visually observe nucleate boiling phenomena in wedged gaps.A flat and uniform copper plate was used as a heater.The surfase of copper plate was ground by polishing method in order to reduce rugosity.A glass plate was used as a sheet for forming a wedged gap in the experiments.Ethanol was the object for observing and measuring.The phenomena showed that boiling nucleation favorably occurs and bubble growing is faster in areas with larger space in narrow gaps.The nucleation on the surface in relatively narrow zone was more difficult and needed higher heat flux than that in larger space zone.Images and figures shot by CCD camera were used to record bubble growth processes.It is observed that nucleation and bubble dynamical evolution in the same gap spacing zone are identical and the growth rate was maintained at a constant value for ≥0.1.
Numerical Investigation of Influence of Rib Orientation on Discharge Coefficients
NI Meng, ZHU Hui-ren, QIU Yun Ding, LIU Song-ling
2004, 19(2): 196-200.
Abstract PDF(684KB) icon1958 icon433
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Numerical simulation was conducted to investigate the flow field of internal cooling passages with both rib-roughened walls and film hole suctions and discharge coefficients of film holes,with rib angles 45°,60°,90°,120°respectively.A finite volume method with unstructured meshes was used to solve the three dimensional imcompressible Navier-Stokes equations.The realizable k-ε turbulence model was used and standard wall function was used for near wall treatment.The coupling of velocity and pressure was performed using the SIMPLE algorithm.The numerical results show that the flow field of internal passages with both rib-roughened walls and film hole suctions was complex,secondary flow produced by ribs changed the angles of the flow near the hole inlet and the hole axis,thus affected discharge coefficients.Discharge coefficients increase with the increase of rib angles.The calculated discharge coefficients are in good agreement with the experimental data.
Experimental Study of Heat Transfer and Total Pressure Drop of a Grid-Ribbed Rectangular Channel
ZHANG Bo, JI Hong-hu, ZHANG Jing-zhou, Gao Chao, Wang Ming
2004, 19(2): 201-205.
Abstract PDF(308KB) icon1704 icon468
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The characteristics of heat transfer and total pressure drop of flow in an internally ribbed rectangular channel were studied experimentally by using two experimental models.The two larger sides of the models were made of ribbed aluminum plates;the two smaller sides were made of bakelite plates and treated as adiabatic surfaces.The acute angle between the ribs and the axis of the channel was defined as the rib angle.For the first experiment model,the rib angles for the two ribbed wall were 45° and -45° respectively,which was known as 45/45 model ,and for the second experiment model,the rib angles were 45° and -60° respectively,named as 45/60 model.All ribbed plates had rib width to pitch ratios t/p of 0.25, rib width to height ratios t/eof 0.3,and rib height to channel height ratios e/H of 0.5.The ribs from each plate of the channel were in contact with each other in their tips,and oriented so as to form a grid pattern.The experimental Reynolds number was in the range of 0.5×105～1.2×105.The experimental results showed that,in comparison to fully developed flow in a smooth pipe of equivalent hydraulic diameter the Nusselt number inside the grid-ribbed rectangular channel was increased up to 5 to 9 times higher,and total pressure drop was enlarged by up to three orders of magnitude.
Influence of Rib's Geometric Parameters upon Heat Transfer and Total Pressure Loss in Grid-Ribbed Channel
ZHANG Bo, JI Hong-hu, ZHANG Jing-zhou, Gao Chao, Wang Ming
2004, 19(2): 206-212.
Abstract PDF(372KB) icon1662 icon450
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The influence of width-to-pitch ratio t/p and width-to-height ratio t/e of ribs upon heat transfer and total pressure loss of rectangular grid-ribbed channel was studied experimentally.Two groups of experimental models were used.The first group was consisted of two ribbed plates with ribs at 45° and -45° to the axis of the channel,respectively,named as 45/45 model.The second group of experimental models was consisted of two plates with rib angle at 45° and,-60° and named as 45/60 model.For these models,t/e varies among 0.25,0.3,0.5,and t/p varies among 0.25,0.33,0.5.The Reynolds numbers varied from 0.5×105 to 1.5×105.The results showed that the models with t/p=0.5 and t/e=0.3 got the best heat transfer enhancement,but also caused highest total pressure drop.The 45/45 model and 45/60 model have similar heat transfer performance,while the latter caused much higher total pressure loss than the former.
Study of the Effusion Wall Film Heat Transfer Coefficients of Impingement/Effusion Double Wall Cooling Method
XU Quan-hong, LIN Yu-zhen, LIU Gao-en
2004, 19(2): 213-218.
Abstract PDF(833KB) icon2359 icon460
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This paper presents the experimental study of effusion wall film heat transfer coefficients for impingement/effusion double wall cooling method,which is one of the advanced cooling methods of combustor liner in aeroengine.The investigation focused on the factors affecting the heat transfer coefficients,which are main flow Reynolds number,blowing ratio and configurations.The heat transfer coefficients were studied using the comparing method,and the basic heat transfer coefficients were compared with classical heat transfer result,showing that the difference was within ±7%.The experimental results showed that the main flow Reynolds number had no effect on the effusion wall film heat transfer coefficient,while the blowing ratio and configurations were the main factors.The more the rows of cooling film,the higher the heat transfer coefficient along the flowing direction.The experimental results were correlated,and the correlation can be used in the heat transfer design and validation of cooling schemes.
An Experimental Study of Cooling Film in Negatively Bowed Cascade with Large Turning Angle
CHEN Fu, YANG Ke, SONG Yan-ping, WANG Zhong-qi
2004, 19(2): 219-223.
Abstract PDF(304KB) icon1763 icon774
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Transverse measurements are carried out at the outlet of the straight and negatively bowed turbine cascades with 106° turning angle respectively with and without cooling air injection from holes of the ten rows and from holes of several rows of the ten rows (totally 26 schemes).Experimental results show that negatively bowed cascade produces more energy loss than the straight one without cooling air injection.Cooling air injection from the holes on the pressure surface and from the holes on the suction surface near the trailing edge can reduce energy losses in both the straight and the negatively bowed cascades.The increase in loss is less in negatively bowed cascade than that in the straight one with cooling air injection from holes of several rows at the leading edge,whereas cooling air injection from holes of several rows at the trailing edge reduces the energy loss in the negatively bowed cascade.
Dynamic Pressure Signal's Processing and Analyzing in Flow Field Based on Wavelet Theory
LI Wen-feng, ZHANG Jin, WANG Yong-sheng
2004, 19(2): 224-228.
Abstract PDF(271KB) icon1435 icon413
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Combined with the acquisition data from experiments of stealthy device in air duct and some turbofan engine,the paper studies the methods and steps of processing and analyzing dynamic pressure signals based on the wavelet theory.The results show that the power spectrum magnitude of signals is mainly fastened within 100 Hz,both range and turbulence of signals are augmented while rotating speed of engine is raised.The lower is the rotating speed,the more intensive are the vortices.It is confirmed that there is a strange attractor in turbulent fluctuation pressure system of flow field,and the correlation dimension D tends from 5 to 6.
Experimental Study of RCS Reduction for a Helicopter Inlet
HAN Dong, GUO Rong-wei, YI Hai-yun, ZHOU Bei-bei
2004, 19(2): 229-232.
Abstract PDF(534KB) icon1757 icon442
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An experimental study of RCS reduction for a helicopter inlet syncretized with engine cabin was completed in vertical and horizontal polarization ways.Meanwhile,the RCS reduction effects were analyzed for various reduction schemes by comparing with RCS of pure metal model.The results show that RCS of this inlet is lower than that of the pure metal model.Sticking radar absorbing materials on front lip,upper lip,inferior lip,output shaft,and engine cabin has best RCS reduction effect.This method can achieve about 8 dB of RCS reduction.Besides,the effect of RCS reduction in vertical polarization way is better than that of in horizontal polarization way.
Effects of Asymmetric Tip Clearance on Axial Flow Compressor Performance
LIANG Wu-chang, CHU Wu-li, ZHU Jun-qiang, SUN Ling
2004, 19(2): 233-236.
Abstract PDF(242KB) icon1675 icon435
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Asymmetry of rotor tip clearance in compressors always exists to some extent.To investigate the effects of rotor tip clearance asymmetry on compressor performances,a series of nonaxisymmetric tip clearance casing configurations were designed and experimented on a low speed,axial flow compressor with a single rotor.For each geometry,experiments were taken under both 5059 r/min and 8130 r/min conversion velocities.According to the experiments,several phenomena could be obtained:(1) With tip clearance asymmetry increasing,the stall points on compressor performance curves shifted to the lower right,compared with the solid casing and symmetric tip clearance.To evaluate such shifting effects quantitatively,two parameters were defined.(2) With tip clearance asymmetry increasing,the average stall performance was also decreased.(3) On the other hand,however,the size of the stall-unstall hysteresis loops on the performance map decreased with the increasing of the tip clearance asymmetry,which showed that it was easier for the compressor to recover from stall.As a whole, the experimental results showed that,such treated casings were detrimental to the compressor performances.
Study of Activating and Binding Mechanisms of Military Aviation Power Purchase
MAO Jing-li, LIANG Gong-qian, LI Ming
2004, 19(2): 237-246.
Abstract PDF(1142KB) icon1409 icon442
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The purchase of military aviation power is a basic way of military aircraft in order to obtain power.Based on the analysis of present mechanisms of military aviation power purchase,and with a view to develop aircraft engine effectiveness,it was researched how to establish activating and binding mechanisms from breaking point of establishing mechanism,the principal-agent model in purchase,and the principle of mechanism design,and the pattern of mechanism design.
A Study and Flight Evaluation of Full Authority Digital Engine Control System
YAO Hua, WANG Guo-xiang
2004, 19(2): 247-253.
Abstract PDF(837KB) icon1969 icon396
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A full authority digital electronic engine control system is developed.Key techniques such as system construction,control rules,fault diagnostic approach,electronic controller,hydraulic mechanical unit,and control software are discussed.Functions and performances of the FADEC system are evaluated by flight testing.As a result,the functions of the control system are enhanced and the performances of engine are improved.
H∞/PI Output Feedback Control of Aero-Engine Under Nonstrict Properness Based on LMI
WANG Xi, TAN Dao-liang
2004, 19(2): 254-258.
Abstract PDF(685KB) icon2019 icon467
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According to the physical meaning of the H∞ norm,a nonstrict proper model is converted into some strict proper model under the equivalence condition of their H_∞ norms.A static output feedback PI controller for the resulting strict proper model is designed on the basis of LMI,and control constraints are taken into consideration in the design process of the controller.An algorithm for solving the static output feedback PI controller is presented.This method is applied to the design procedure of aero-engine controller.The dynamical and static performances of the aero-engine control system are verified at different partitioned regions of flight envelope.
Distributed Parameter Control method for Hypersonic Jets
YU Da-ren, CUI Tao, BAO Wen
2004, 19(2): 259-264.
Abstract PDF(985KB) icon1828 icon403
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Hypersonic jets show obvious distributed parameter characteristics,and the concentrated parameter control method is hard to function.In this paper,the distributed parameter control method for hypersonic jets which is the succession and breakthrough of traditional concentrated parameter control method is put forward after analyzing the development of distributed parameter control theory and corresponding circumjacent subjects.The new principles and methods of distributed parameter control may have an impact on the operation and design of hypersonic jets.
Experimental Investigation of Surface Static Pressure Distributions in Different Swept Compressor Cascades
ZHAO Gui-jie, CHEN Fu, SONG Yan-ping, BIAN Zhao-xi, WANG Zhong-qi
2004, 19(2): 265-269.
Abstract PDF(620KB) icon1681 icon502
Abstract:
The experimental study of static pressure distribution on the surfaces of rectangular compressor cascades with different swept blades shows the forward swept cascade weakens the cross pressure gradient in the flow passage,establishes opposite "C" type pressure distribution along the blade height,which helps reduce the accumulation of low energy fluid in the suction corner region,but increases the loss near the midspan.The forward swept-positive curved cascade,compared to the forward swept cascade,further strengthens the capacity of reducing the loss near the endwall and delaying corner stall.
Study of a New Method for Giving Warning Signals of Instability
ZHANG Jing-xuan
2004, 19(2): 270-277.
Abstract PDF(391KB) icon1719 icon389
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A new method has been developed to give early warning signals just before a compressor runs into instability. Analyses based on prestall pressure signals of several axial compressors reveal that the dynamic pressure energy accumulation in a compressor just before the instability could be used as a precursor signature of the instability.It is illustrated that by using the appropriate RMS of the casing static pressure over the rotor tip an early warning could be obtained about 1～2 seconds before the onset of the instability.This is particularly important because the method is applicable to the spike type stall inceptions as well as the model type ones,the former usually appears abruptly and does not have a precursor.
An Experimental Study of Cooling Film in Negatively Bowed Cascade with Large Turning Angle
LI Yue-sen, YE Ding-you, LI Feng-xiang
2004, 19(2): 278-282.
Abstract PDF(674KB) icon1427 icon420
Abstract:
Transverse measurements are carried out at the outlet of the straight and negatively bowed turbine cascades with 106° turning angle respectively with and without cooling air injection from holes of the ten rows and from holes of several rows of the ten rows (totally 26 schemes).Experimental results show that negatively bowed cascade produces more energy loss than the straight one without cooling air injection.Cooling air injection from the holes on the pressure surface and from the holes on the suction surface near the trailing edge can reduce energy losses in both the straight and the negatively bowed cascades.The increase in loss is less in negatively bowed cascade than that in the straight one with cooling air injection from holes of several rows at the leading edge,whereas cooling air injection from holes of several rows at the trailing edge reduces the energy loss in the negatively bowed cascade.
3-Dimensional FEM Simulation of Dynamic Characteristics of Cracked Gear
SHAO Ren-ping, GUO Wan-lin, LI Chun
2004, 19(2): 283-288.
Abstract PDF(830KB) icon1711 icon433
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The 3-dimensional FEM dynamic model of a cracked gear structure is established,the dynamic characteristics,i.e.,the natural frequency,the mode shape,the dynamic stress and so on,due to crack of gear tooth are analyzed in this paper.The influence of crack position and crack depth etc.on dynamic characteristics of gear is investigated by using computer simulation and the FEM.It shows that the influence of crack depth and crack position on both natural frequency and mode shape of gear is significant.The natural frequency drops and mode shape changes when a crack started.This natural frequency drops with the increase of crack depth,but the influence of crack position on both natural frequency and mode shape is greater than that of the crack depth.The natural frequency of gear drops more when crack locate at the tooth root in comparison with that of the gear when crack appears at the tooth tip.When a crack starts,the mode pattern of gear structure becomes very different from that of g gear uncracked.when a crack starts.The amplitude is augmented and the dynamic stress of gear changes in the crack neighborhood.The present study is important and usuful for damage detection and fault diagnosis.

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