2013 Vol. 28, No. 8

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Display Method:
One-dimensional unsteady analytical model of rotating passage
WU Hong, LI Peng, LIU Dong-dong, TAO Zhi
2013, 28(8): 1681-1688.
Abstract PDF(1111KB) icon2045 icon1364
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The main purpose of the research was to investigate one-dimensional flow and heat transfer activity in rotating passage of secondary air system in aero-engines by method of characteristics.Partial differential equations of rotating passage generally integrating invariability of flow area,friction and heat transfer were transformed to ordinary differential equations,considering the influence of the centrifugal force by rotation;and the Colebrook White equation was used to predict its loss performance,so one-dimensional characteristic numerical solutions of pressure,flow,temperature and other parameters in rotating passage were derived.Results were verified by commercial software Fluent,showing that the method of characteristics is visual by utilizing pressure wave to describe the flow in rotating passage,with the error not exceeding 5%.Thus,it is an efficient way of one-dimensional unsteady research on rotating passage in secondary air system.
Performance comparative experiment on flame tubes of a certain combustor
LI Ming, WU Er-ping, SUO Jian-qin, LIANG Hong-xia
2013, 28(8): 1689-1695.
Abstract PDF(1143KB) icon1690 icon1201
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In order to examine performance of domestic flame tube for a certain combustor on an active service aero-engine,on the test platform for combustor by means of the continuous air resource and sector rig,comparative experiments of the combustion efficiency characteristic,exit and wall temperature distribution and lean blowout characteristic were conducted to simulate the combustor maximum rating between original and domestic flame tubes. The experimental results show that two kinds of flame tube have the same combustion efficiency characteristic,and the combustion efficiency values are approximate,but the domestic one is 0.5% higher than the original one under identical state.Exit temperature fields are similar,of which indexes of quality are approximate;within reasonable range,the difference of outlet temperature distribution factor is 1% and that of radial temperature distribution factor is 1.3%.Wall temperature distributions are similar;the maximum difference of temperature is 50K on identical position and the domestic one is higher than the original one.Lean blowout characteristics are consistent and the original one is better under 150m/s inlet airflow velocity.
Backfire tests of an aircraft piston engine
ZHANG Zhi-qiang, HE Jun, WEI Ming-shan, ZHANG Jin, LIU Xiao-zhu
2013, 28(8): 1696-1701.
Abstract PDF(1094KB) icon2209 icon1319
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In order to solve the problem of one aircraft piston engine that the backfire test must be conducted to acquire the airworthiness type certificate (TC) pursuant to article 33.51 of part CCAR-33 “Airworthiness standard of aircraft piston engine”,a new test method was proposed based on the photoelectric signals through the study on single-cylinder engine.The experiments showed that the proposed method can well detect the backfire.Based on the above research,the inducing backfire method was conducted through reducing the flow rate of fuel by operating lean/rich joystick.The experiments on the tested engine show the engine is tendency to backfire in its operating conditions and the engine works well after 57 times artificial induction backfire on the tested engine.The tested engine meets the requirements of airworthiness certification.
Comparative investigation of infrared radiation characteristics of axisymmetrical individual and mixing exhaust systems in turbofan engine
SHI Xiao-juan, JI Hong-hu, SI Ren, LIAO Hua-lin
2013, 28(8): 1702-1710.
Abstract PDF(1092KB) icon2056 icon1389
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The infrared radiation (IR) characteristics of axisymmetrical individual and mixing exhaust systems in turbofan engine were investigated with the method of numerical simulation.The flow fields of exhaust systems were simulated with commercial software.The IR characteristics were calculated with an IR analysis software based on reverse Monte-carlo method developed by our research group.The IR characteristics in the waveband of 3-5μm of the two exhaust systems and the IR contributions of different solid parts in the nozzles in different detection directions were calculated and analyzed.In the process of IR computation,the emission and reflection of the wall in the nozzle and the absorption and emission of CO2,H2O and CO in the gas jet were considered.The results show that the spatial distribution characteristics of IR of the two exhaust systems are different.The integral IR intensity of the mixing exhaust nozzle is less than that of the individual one except in the azimuth angles of 0° to 10°.
Effects of porting arrangements on intake swirl and scavenging performance
CAO Jiao-kun, DING Shui-ting, DU Fa-rong, WANG Zhen-yu
2013, 28(8): 1711-1718.
Abstract PDF(966KB) icon1784 icon1207
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Effects of porting arrangements on intake swirl and scavenging performance were investigated numerically.A three-dimensional transient numerical model was established for the in-cylinder processes.Intake swirl was introduced by changing port tangential inclinations and scavenging performance was evaluated by normalized carbon dioxide mass fraction.The intake swirl intensity and scavenging performance with different porting arrangements were compared.The results show: (1) Rotation flow including swirl can be generated by port tangential inclination arrangements,and the swirl approximates to solid-body swirl approaching the top dead center.(2) Intake swirl results in short-circuiting during the scavenge processes and a concentrated carbon dioxide central core.(3) The short-circuiting can be reduced by increasing the axial inclination of inlet ports or extending the distance between inlet and exhaust ports in the flow direction.Swirl intensity can be decreased by reducing scavenge port tangential inclinations,leading to increase of short-circuiting.
Experimental investigation on cold flow field characteristics of low emission trapped-vortex combustor
JIANG Bo, HE Xiao-min, JIN Yi, WU Ze-jun, DING Guo-yu
2013, 28(8): 1719-1726.
Abstract PDF(1748KB) icon2323 icon1215
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Particle image velocimetry (PIV) was used to perform experimental investigation on cold flow field characteristics of low emission trapped-vortex combustor(TVC) model.The varieties of the cold flow field characteristics and the total pressure loss coefficient were obtained.The results show that vortex structures are stable in the model of low emission TVC,and the double vortex structure exists in the trapped vortex area located in the rear of the mainstream,as well as the single vortex structure exists in the trapped vortex area located in the rear of flame transport board.The double vortex system transforms into the single vortex system and the vortex center positions show a little change in these different sections.The center positions of double vortex and single vortex in each section do not change with the inlet Mach number (0.15~0.30) increasing,but the primary vortex area in double vortex system increases,and the secondary vortex area also changes,which is the largest at Mach number of 0.2.The velocities of airflow in the primary combustion zone and the edge of the vortex,the vortexes strength,and the total pressure loss coefficient increase with the inlet Mach number changing from 0.15 to 0.3.
Optical measurement and characteristic analysis of aeroengine combustor primary zone with counter-rotating swirler
CHEN Min, SONG Wen-yan, XIAO Yin-li, CHEN Liang, LI Jian-ping
2013, 28(8): 1727-1735.
Abstract PDF(1227KB) icon1805 icon1154
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For an aeroengine annular combustor model,coherent anti-Stokes Raman scattering (CARS) and tunable diode laser absorption spectroscopy (TDLAS) were used to measure temperature in primary zone (PZ) for modeling condition(Case 2).Based on Fluent 12.0 software,two different non-premixed combustion models equilibrium model (EM) and steady laminar flamelet (SLF) model were adopted to calculate the combustor performances for the same case.Then comparison between spectral measured temperature and numerical simulated one shows that higher and more accurate prediction were achieved by EM.What's more,the errors between EM calculation and CARS measurement are less than 6%.For cold flow condition(Case 1),not only detailed analysis of flow field in PZ was made,but also the influence of primary jet on recirculation zone was investigated.Because of the advantage EM was used for full pressure condition (Case 3) to analyze reaction flow field in PZ and calculate combustor performances,including combustion efficiency(0.97),overall temperature distribution factor (OTDF)(0.312),etc.These results indicate reasonable heat transfer and combustion phenomena in combustor model.
Effect of ratio of height to width of lobe on performance of forced mixing exhaust system
LI Teng, LIU Yong-hong, XIE Yi, SHAO Wan-ren, WU Fei
2013, 28(8): 1736-1743.
Abstract PDF(1037KB) icon1855 icon1171
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The effects of different ratios of height to width of lobe mixers on the flow field, thermal mixing efficiency, total-pressure recovery coefficient and thrust coefficient were studied when the areas of inner duct and outlet duct kept constant in turbofan aero-engine forced mixing exhaust system. Geometric models with various ratios of height to width of lobed mixer in turbofan aero-engine forced mixing exhaust system were built, and the numerical simulation methods based on Navier-Stokes equations were conducted. The results indicate that at the exit section, if the areas of inner duct and outlet duct keep constant, in a range of ratios of height to width of 2 to 4.5, the thermal efficiency of lobed mixer has the trend of increasing, decreasing and increasing again, and at last the inflection points of efficiency function curve are at 3 and 3.21. In addition, with the increase of ratio of height to width, the total-pressure recovery coefficient and thrust coefficient also decrease.
Numerical simulation of coolant air injection at leading edge of turbine stator with rows of holes
ZHANG Cun-yuan, ZHONG Yi-cheng, XU Wei-zu, PAN Shang-neng
2013, 28(8): 1744-1751.
Abstract PDF(1267KB) icon1704 icon1184
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The leading edge of a three-dimensional screwy coolant turbine stator was numerically simulated when the injection angles of the row of holes were 30°,60° and 90° respectively,and the lateral direction angles were all 90°.Source point and hole jet methods were adopted separately to study comparatively the aerodynamic performance and cooling characteristics on the leading edge;the mechanism of coolant injection and the influence of different injection angles on the field of cascade flow and cooling characteristics were analyzed.The results show that film holes influence obviously the flow field near the leading edge of about 10% axial chord length range,and the cooling effect covers the entire leaf.The pressure of source point method is very close to non-cooled turbine.With the decrease of cooling air radial injection angle,the surface temperature of real holes model drops by 8% to 16%,but that of source point model by 21% to 23%.The results of source point method can not be taken as a quantitative basis for assessment in engineering.
Effect of Knudsen number on microscale similar flow characteristics
XU Yan-zhi, ZHU Hui-ren, ZHENG Jie
2013, 28(8): 1752-1758.
Abstract PDF(991KB) icon5988 icon3897
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Four similar hole models with the aperture of 3,1,0.5 and 0.3mm were selected,with the fluid regarded as continuous medium to investigate the effect of Knudsen number on the characteristics of microscale similar flow.The mass flow rate coefficient was calculated by numerical simulation when the Knudsen number of fluid with each scale pore was variable and constant at the same Reynolds number,and then the internal flow field was analyzed.The results show that when the Knudsen numbers of the four hole models are equal,the internal flow fields and the mass flow rate coefficients of different scale pores show a better similarity at the same Reynolds number,so it is required to ensure the same Knudsen number to get more accurate results in investigating the flow characteristics of microscale structure by amplificatory models.
Lean blowout mechanism of coupled recirculation zone in concentric staged combustor
ZOU Bo-wen, XU Quan-hong, CAO Wen-yu, ZHANG Chi, LIN Yu-zhen
2013, 28(8): 1759-1763.
Abstract PDF(824KB) icon2135 icon1351
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Experiments under atmosphere and idle states were carried out to analyze the mechanism of lean blowout by numerical simulation of coupled recirculation zone formed in main stage and pilot stage.The results show that unlike conventional combustor,the lean blowout fuel-air ratio of concentric staged combustor is determined by coupled recirculation zone formed by pilot and main swirlers.The recirculating flow in the coupled zone is dominated by the main stage in this concentric staged combustor,and air entrainment from the main stage is 4.3 times of that from the pilot stage itself,leading to the lean blowout equivalence ratio of pilot stage up to 2 to 2.5,far higher than that of 0.4 to 0.5 of conventional combustor dome.
Adaptive incremental particle filter method
FU Hui-min, WU Yun-zhang, LOU Tai-shan
2013, 28(8): 1764-1768.
Abstract PDF(919KB) icon1743 icon1339
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An adaptive incremental particle filter (AIPF) model was put forward, and its concept, model, basic equations and key calculative steps were given. For the measurement data with unknown system errors in many actual engineering (such as deep space exploration) and the considerable filter errors, accurate measurement model cannot be established. The presented AIPF method applied the accurate incremental particle filter model to automatically conduct adaptive adjustment of the number of particles, so the effects of these unknown measurement system errors and the lack of particles were eliminated. This method can automatically adjust the particles (sample points) and finally improve the nonlinear filtering accuracy. In simulation, the mean and covariance of filtering error decrease by 3.8% and 19.6%, respectively. The method can effectively improve the performance of filter, so it can be easily applied to engineering with simple calculation process.
Simulation of extrusion strengthening of pressure equalizing hole of an engine compressor disc and design of extrusion heads
YANG Xing-yu, DONG Li-wei, ZHENG Xiao-mei, ZHAO Fu-xing
2013, 28(8): 1769-1776.
Abstract PDF(1005KB) icon1178 icon987
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Statics solution algorithm was adopted in elastic-plastic finite element analysis program to simulate the extrusion strengthening process.Influences of parameters,such as friction coefficient,extrusion times,extrusion amount,restriction way,fillet radius and matching mode,on the residual stress distribution were analyzed.According to specific configuration of the pressure equalizing hole of the engine compressor disc,three different kinds of extrusion heads were designed,including:one-sided extrusion head,cylindrical extrusion head and T-shaped extrusion head.Two kinds of materials (stainless steel 1Cr11Ni2W2MoV and high temperature nickel-alloy ЗП742) were used to design and manufacture the simulation samples of sheets with holes.Edges of holes were strengthened using two above-mentioned coldworking techniques.The experiment results show that T-shaped extrusion techniques can efficiently and conveniently improve fatigue strength of sheets with holes.Numerical simulations were compared with experimental results,showing that statics general program can be used to simulate extrusion progress of sheet metal specimens with holes,and provide a guidance to extrusion strengthening research.
Spraying quality inspection of thermal barrier coating by micro-computed tomography
AO Bo, WANG Chan, DENG Cui-zhen, WU Guan-hua
2013, 28(8): 1777-1783.
Abstract PDF(1144KB) icon1373 icon1114
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Specimen of thermal barrier coating (TBC) was inspected by high resolution X-ray imaging with a microfocus X-ray source,while multiscale contrast enhancement for X-ray image was performed,and the contrast between the coating and substrate was improved.X-ray images show that thickness of TBC is different in different positions,and many voids may exist in the interior of TBC.The specimen of TBC was scanned and reconstructed by high resolution microfocus X-ray computed tomography(CT),and slice images in different cross sections were obtained.CT images show that voids exist in TBC,and the size and quantity of voids are different in different cross sections.Combined with slice image analysis from three coordinate directions,thickness of TBC along deepth direction was analyzed,and two-dimensional distribution of TBC thickness was achieved.Average thickness of TBC is approximately 40 μm.The slice images from slice 850 to slice 1131 along deepth direction were visualized by the software of VGstudio MAX,and 3-D distribution of voids was displayed.Research results show that micro-computed tomography can be used to inspect the quality of thermal barrier coating.
Reliability robust design optimization based on response surface method
PENG Mao-lin, YANG Zi-chun, CAO Yue-yun, CHU Zhu-li
2013, 28(8): 1784-1790.
Abstract PDF(946KB) icon1818 icon1067
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To solve the problem of reliability robust design optimization of structure with implicit limit state functions and limit output performance functions,the robustness of the performance,reliability sensitivity robust and six sigma robust design were integrated,and a reliability robust design optimization model based on response surface method was presented involving the detailed calculation processes of the method.The second-degree polynomials were introduced to simulate the output performance functions and the limit state functions of the structure.The equations of the first order reliability index,the mean value and the standard deviation of the structure were calculated based on the response function.Then taking the structural reliability as the basic constraint condition,the final optimization result with the sequential quadratic programming method was obtained.Finally the example was introduced to explain and validate the model.The method was used to design the model lines of a gas turbine blade.After design optimization,the results indicate that the aerodynamic efficiencies of the guide blade and working blade increase by 1.5% and 6.4% respectively,and the maximum stress and the maximum strain of the working blade decrease by 7.9% and 5.6% respectively.The intensity structural reliability of the working blade increases from 91.3% to 99.9%.
Vibration characteristics of gas bearing-rotor system of high-speed permanent magnet machine
HAN Dong-jiang, YANG Jin-fu, GENG Jia-min, HE Min, ZHU Li-min
2013, 28(8): 1791-1796.
Abstract PDF(924KB) icon1518 icon1062
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In the 45kW high-speed permanent magnet machine test rig,permanent magnet machine's raising speed experiment was made to research the influence of bearings supply pressure and the raising speed rate on the shaft stability.Bifurcation plot,frequency-domain characteristic and axes locus were analyzed to find sub-synchronous vibration.The result shows that:adjusting the bearing supply pressure can control bifurcation point from 18400r/min to 38900r/min, and eliminate half-speed whirling under 38900r/min.To change the raising speed rate (from 825(r/min ) /s to 660(r/min ) /s) can reduce power frequency vibration amplitude from 95μm to 75μm.
Improved method of BLISS based on response surface
ZHANG Dai-yu, SONG Bao-wei, WANG Peng, DONG Hua-chao
2013, 28(8): 1797-1802.
Abstract PDF(827KB) icon1483 icon930
Abstract:
Based on the analysis of the BLISS (bi-level integrated system synthesis),an improved method of BLISS was proposed,and the response surface based on design of experiments was introduced to make an approximation in both the subsystem and the system-level meanwhile the parameters of moving step were set,making unnecessary for complex sensitivity analysis;the movement limits of each iterative optimization in the BLISS method,and the optimization iterations and the possibility of falling into local optimum were reduced.Finally,two specific examples were given to verify above method compared with traditional BLISS.The results show that the optimization iterations of above methods were respectively reduced by 57.9% and 70.3%,respectively.
Comparison of flutter characteristics of forward/ backward swept fan blades
FU Zhi-zhong, WANG Yan-rong
2013, 28(8): 1803-1807.
Abstract PDF(804KB) icon1987 icon1198
Abstract:
The effects of mode shape and inter blade phase angle(IBPA) on aeroelasticity stability of forward and backward swept blades were investigated through numerical flutter analysis and comparison based on the energy method.Results show that,for the first three vibration modes,aerodynamic modal damping ratio(AMDR) of forward swept blades corresponding to the coupling mode has the highest value of 0.801%,and that of backward swept blades corresponding to the coupling mode has the lowest value of 0.248%.IBPA has significant effects on AMDR for two kinds of swept blades.AMDR corresponding to forward travelling wave is lower than that corresponding to backward travelling wave for forward swept blades vibration in the 1st flapping mode at the same IBPA,while it is contrary for the backward swept blades;forward swept blades have better aeroelasticity than backward swept ones at arbitrary IBPA when blades vibrate in the 1st flapping mode.
Experiments of Reynolds stress manipulation during burst by blow/suction disturbance
LIU Wei, JIANG Nan, GU Run-ping
2013, 28(8): 1808-1817.
Abstract PDF(1338KB) icon1311 icon963
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The time sequence signals of instantaneous longitudinal,normal and spanwise velocity components at different vertical locations on the turbulent boundary layer over a flat plate were finely measured by constant temperature anemometry and double-sensor hot-wire probe in a wind tunnel.By the criteria of the module-maximum of locally averaged longitudinal velocity structure function,the conditional phase-averaged waveforms of different velocity components and Reynolds stress were detected during the burst.After disturbance,it is found that the friction coefficients and the Reynolds stress are reduced;the phase-differences between the phase-averaged waveforms of longitudinal vertical velocity and the spanwise velocity components are changed.When their phase differences are about odd times of π/2,the Reynolds stress is depressed to about zero.The mechanisms of production,diffusion and transportation of Reynolds stress are changed in wall-bounded turbulent flow and the Reynolds stresses are restrained to a certain degree.
Calculation and analysis on air inlet/engine integrated in fast maneuvering flight
TIAN Jin-hu, QIAO Wei-yang, PENG Sheng-hong
2013, 28(8): 1818-1827.
Abstract PDF(1559KB) icon1632 icon1008
Abstract:
Based on an air inlet/engine integrated dynamic simulation system,the engine performance parameters were investigated and obtained in fast maneuvering flight.The numerical calculation shows that fast-changing exterior turbulence reflects on more dynamic fluctuation of thermal cycle parameters and performance parameters,due to the history of engine fuel mass flow,engine thrust descend degree minishs,on the contrary,engine specific fuel consumption ascends with increase of attack angle.
Aerodynamic optimization method for duct design
YE Kun, YE Zheng-yin, QU Zhan
2013, 28(8): 1828-1835.
Abstract PDF(1035KB) icon1825 icon1187
Abstract:
Based on momentum source method of calculating the ducted fan aerodynamic performance,the response surface method and neural network method were applied to aerodynamic optimization design of the NASA duct,and the optimization results were verified by CFD method.The optimization design results show that the two methods have achieved good effect.In the state of hovering,compared with the original duct,duct lift increased by 19.4% based on the response surface method,and duct lift increased by 21.2% based on the neural network method.In addition,in order to study the mechanism of duct lift more carefully,the duct was modeled,and partitioning method was adopted to divide the duct into 6 zones to obtain the duct lift distribution in the 6 regions.This shows that negative pressure formed on duct lip is a main factor to produce additional duct lift,and the duct lip near the interior duct provides higher lift.This optimization method can be effectively applied to the ducted fan aerodynamic optimization design.
Static aeroelastic optimization of hypersonic aircraft based on high-fidelity model
SU Hua, GU Liang-xian, GONG Chun-lin
2013, 28(8): 1836-1842.
Abstract PDF(924KB) icon1528 icon1071
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Static aeroelastic optimization was proposed for an entire aircraft vehicle based on computational fluid dynamics (CFD) and computational structural dynamics (CSD) coupling numerical computational methodology. To solve the problem of automatic modeling and computational demand on multidisciplinary optimization based on high-fidelity model, a geometric master model technology was presented to generate the CFD/CSD integrated models, an improved constant volume tetrahedral (CVT) method based on elements was used for the grid deformation and force transition between the CFD and CSD mesh, and the response surface model (RSM) was used in stead of the traditional optimization algorithms. The above methods were validated by AGARD 445.6 wing static aeroelastic analysis. A hypersonic aircraft multi-objective optimization based on RSM was accomplished through CFD/CSD static aeroelastic optimization. The optimized aircraft lift-to-drag ratio increased by 16%, structural weight reduced by 9%, and the fitting error of RSM was less than 1.5%. Results show the CFD/CSD integrated modeling and optimization method could solve effectively the static aeroelastic optimization problem with high-fidelity models.
Preliminary study on variable-geometry axisymmetric inlet with first cone pivoting
MIAO Hai-feng, XIE Lü-rong, GUO Rong-wei
2013, 28(8): 1843-1850.
Abstract PDF(1280KB) icon1504 icon1074
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To achieve good characteristics of an axisymmetric supersonic mixed-compression inlet at different angles of attack,a feasible and available variable-geometry technique was proposed and demonstrated by changing the shock system structure of the forebody with a pivoting first cone.The 3-D flow field and performance characteristics of the variable-geometry inlet at Mach 3 and 4 were investigated numerically over a wide range of angles of attack,and the results were compared with those of the conventional fixed-geometry inlet.The results indicate:(1) By rotating the first cone,the mass flow coefficient of the inlet is improved and the low-energy flow accumulation at the leeward side is relieved effectively at high angle of attack.(2) There exists an optimum value of the angle of rotation,enabling the inlet to reach the highest performance at given high angle of attack.(3) With the increase of angle of attack,the optimum angle of rotation increases,and the thrust augmentation also increases to 7.7% at Mach 3 and angle of attack of 14°.
Over/under type inlet scheme for turbine-based combined cycle engine
WANG Ya-gang, YUAN Hua-cheng, GUO Rong-wei
2013, 28(8): 1851-1857.
Abstract PDF(963KB) icon2229 icon1110
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A design scheme of variable geometry over/under type inlet for turbine-based combined cycle engine was presented.Numerical simulation was carried out to investigate the variation of aerodynamic performance of this variable geometry inlet scheme along flight envelop.On basis of this,the design parameters and geometry modulating law were studied.A superior operating law was acquired.The inlet performance of typical work point was provided.Results indicate that the total pressure recovery coefficients at throat section of turbine inlet and exit section of scramjet inlet are not less than 0.69 and 0.38 under different freestream Mach number.
Optimization design of vaneless inlet particle separator based on hybrid algorithm
YU Guang-yuan, LEI Yu-bing
2013, 28(8): 1858-1864.
Abstract PDF(834KB) icon1669 icon1025
Abstract:
To reduce flow loss and simplify the structure of the inlet particle separator(IPS),hybrid optimization algorithm was introduced into the IPS optimization design.Firstly,four order spline curve was adopted as parameterized description of the IPS model and an automated simulation process was established.Optimal Latin hypercube design(OLHD) method was used to obtain the sample points,and an elliptical radial basis function(EBF) surrogate model was established to substitute the simulation code.Then non-dominated sorting genetic algorithm (NSGA-Ⅱ) was used for multi-objective optimization based on surrogate model,and finally non-linear programming by quadratic Lagrangian (NLPQL) algorithm was applied to local optimization.As a result,a new configuration was obtained,with the scavenge efficiency of C-spec distribution improved to 100% and 86.7% for AC coarse distribution fine sand and total pressure reduced to less than 0.6% with smaller main outlet pressure distortion.
Effects of Coulomb friction in foil structure on foil journal bearing performance
XU Fang-cheng, LIU Zhan-sheng, ZHANG Guang-hui, HUANG Fei-lin
2013, 28(8): 1865-1875.
Abstract PDF(1323KB) icon1842 icon1056
Abstract:
The Coulomb friction model of foil structure of bump foil journal bearing was developed by using finite element mothod.Through changing friction coefficients between top foil and bump foil,bump foil and bearing housing,the stiffness of foil strucure of Coulomb friction model and linear spring model from literatures were compared under various load distributions,and the effects of Coulomb friction on stiffness of bump foil were studied.Then,by using finite element mothod and finite difference method,the compressible gas lubricated Reynolds equation and the film thickness equation were solved together.Predictions of the minimum gas film thickness on bearing mid-plane for increasing static loads and load capacity versus eccentricity ratio at two speeds were obtained.The numerical results of this finite element model were compared with those of linear spring model and rigid surface gas bearing,and the predicted film thickness was also compared with test data.The results indicate that Coulomb friction force can enhance the stiffness of bump foil.With the increase of friction coefficient,the stiffness of bump foil and number of bump foil with both ends fixed are also increased,so the surface of foil bearing is made to be hard,and static performance of bearing is similar to that of rigid bearing.Moreover,when the bearing load capacity is fixed, the minimum film thickness decreases with the increase of foil friction coefficient.
Static characteristics of oil-lubricated multi-leaf foil bearing with compliant support
HU Li-guo, ZHANG Guang-hui, XIE Liang, LIU Zhan-sheng, YAN Jia-jia, XU Fang-cheng
2013, 28(8): 1876-1884.
Abstract PDF(1112KB) icon1584 icon967
Abstract:
Multi-leaf foil bearing with compliant support was proposed in order to increase the bearing load capacity.Based on the flexibility matrix theory,the foil deformation was calculated theoretically,and compared with the finite element analysis results to verify the accuracy of the proposed method.The relationship between the oil film thickness and foil deformation was established.The static characteristics of the oil-lubricated foil bearing were studied numerically and compared with those of multi-leaf foil bearing without compliant support.The static characteristic test rig for oil-lubricated foil bearing was constructed,and then the load capacity of the foil bearing was obtained experimentally.The results indicate that the load capacity of multi-leaf foil bearing with compliant support is bigger than that without compliant support.When the rotating speed is 30000r/min,the load capacity of the bearing increases to 109% compared with the bearing without compliant support.As the rotating speed increases,the tendency for the increment is more obvious.The experimental load capacity agrees well with the theoretical value,and the difference between the results (measured and theoretical results) is 2.7%.
Gas path analysis based on multi-sources diagnostics information fusion
SUN Jian-zhong, ZUO Hong-fu
2013, 28(8): 1885-1896.
Abstract PDF(1217KB) icon1779 icon1033
Abstract:
Considering the poor accuracy and precision of the gas path analysis (GPA) results due to lack of enough measured gas path parameters and the associated uncertainty,a Bayesian network based multi-source diagnostics information fusion mechanism was proposed to improve the performance of the GPA.The Bayesian network based GPA (BN-GPA) was introduced briefly,then an improved BN-GPA was developed to incorporate diagnostics information from multi sources.In the framework based on the diagnostics information inferred from the measured gas path parameters,other diagnostics information was incorporated into the Bayesian network by the fault mode prior probability table.The results of the simulation show that by fusing the multi sources information, the fault mode which cannot be identified by the traditional GPA now can be identified accurately with reduced variance for the estimation of the health parameters; In another case where the standard deviation of the measurement noise is doubled and the deviations of the health parameters of the faulty components are set less than 1%, the estimation results of the health parameters are still relative accurate with the standard deviation of the estimation result less than 0.1%.
Intelligent emergency control system of a certain turbofan engine
CHEN Xiao-lei, GUO Ying-qing, ZHANG Shu-gang
2013, 28(8): 1897-1904.
Abstract PDF(1008KB) icon1560 icon1076
Abstract:
Taking a certain turbofan engine as an example,the emergency control of aero-engine was introduced,and two emergency control modes were given:overthrust control and fast response control.The simulation results show that after constraint release,overthrust control can provide an additional 16.6% of the engine's thrust,but at the same time,the temperature of turbine inlet rises by 10.8%;and under fast response control,the rise time of low pressure rotor reduces to 1.675s from 2s,however the stability margin of compressor decreases by 6.05% and the thermo-mechanical fatigue life of the turbine guide vane declines by 5.16%.
Applicability of blended blade and endwall under different operating conditions
TIAN Yong, JI Lu-cheng, LI Wei-wei, YI Wei-lin, XIAO Yun-han
2013, 28(8): 1905-1913.
Abstract PDF(1325KB) icon1742 icon1165
Abstract:
To continue the previous work,NASA rotor 67 redesigned with blended blade and endwall (BBEW) was further studied and focused on assessing the influences of three different rotating speeds,i.e.100%,90% and 80% of full speed,at two different Reynolds numbers,under ground condition and 10000-meter high altitude condition.Numerical tests show that under almost all the operating conditions in relation to original model,BBEW model can improve performance such as total pressure ratio and isentropic efficiency,particularly under conditions of low rotating speeds and low Reynolds numbers,with the efficiency up by 0.6% to 0.8%.This indicates that BBEW has broad applications under operating conditions,serving as another important aspect of full 3-D blade in addition to sweep and bow techniques.
Effect of chamber structure on fuel regression rate and performance of hybrid rocket motor
WANG Peng-fei, RAO Da-lin, TIAN Hui, CAI Guo-biao
2013, 28(8): 1914-1920.
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Abstract:
The flow-field and combustion processes of hybrid rocket with different chamber structures under 2-D and axisymmetric environment was numerically calculated.Analytical result indicates that the fuel regression rate increases with the increase of pre-chamber length,but the acceleration is smaller and smaller,and the tendency to characteristic velocity and vacuum specific impulse with increasing pre-chamber is bigger at first and then smaller and keeps steady in the end.The fuel regression rate does not change when the post-chamber extends,and the characteristic velocity and vacuum specific impulse become higher with longer post-chamber.The draw ratio of grain does not affect the fuel regression rate distribution along the axis under the condition of the same oxidizer mass flux.Both draw ratio and average fuel regression rate have the same changing trend,but speed of the increase of average fuel regression rate is smaller and smaller.The characteristic velocity increases with draw ratio firstly and then decreases,and the position of the maximum is around draw ratio of 10.0.Fuel regression rate increases with draw ratio with the same theoretical oxygen/fuel ratio,but this does not affect its distribution tendency;combustion efficiency reduces firstly and then increases gradually with of the increase of draw ratio;actual oxygen/fuel ratio decreases gradually when draw ratio becomes large and the change tendency is slower and slower.

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