2016 Vol. 31, No. 1

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Random uncertainty modeling and vibration analysis of rotor-foundation system
YOU Zhen-zhou, HUANG Qi-xiang, WANG Feng, XIONG Xin
2016, 31(1): 1-9. doi: 10.13224/j.cnki.jasp.2016.01.001
Abstract PDF(1234KB) icon1381 icon499
Abstract:
Taking the Jeffcott rotor with elastic support as the research object, the dynamic differential equation of rotor-foundation external random excitation system with rubbing faults was built in consideration of the effect of the external random excitation on the foundation and rubbing faults between stator and rotor. The numerical simulation was employed to obtain the system responses with the effect of the external random excitation, and the axis orbit, frequency spectrum and Poincaré sections were used to anlyse the effect on rotor-foundation system with the variation of the external random excitation. The results show that: the vibration mode (such as frequency and waveform) could be changed by the intensity and spectral width of the external random excitation and frequency of the external periodic excitation. And it will cause complex dynamic behaviors of rotor such as cycle, period doubling and chaos.
Application of metal additive manufacturing in aero-engine
ZHANG Xiao-wei
2016, 31(1): 10-16. doi: 10.13224/j.cnki.jasp.2016.01.002
Abstract PDF(775KB) icon1764 icon792
Abstract:
Additive manufacturing (AM), as one of the most competitive manufacture technologies around the world, was investigated for the application of metal parts in aero-engine. The principles, connotations and development of typical AM technologies applied for metal materials' direct energy deposit (DED) and powder bed fusion (PBF), were analyzed in emphasis. Furthermore, the applications of AM in the development of commercialized aero-engine parts, such as fuel nozzle and low pressure turbine blade, and in the repairing of aero-engine parts, such as turbine blade, whole blisk and gear, were summarized. It is indicated that metal AM technology is suitable for aero-engine parts made from metal material, such as titanium alloy, nickel-based alloy, titanium-aluminium (Ti-Al) alloy, etc. AM technology shows the advantages in design, manufacture and affordability, which are important for the future development of aero-engine industry.
Numerical simulation method of low-velocity impact on SMA composite material
HU Dian-yin, PENG Jing-fu, JIA Ao, WANG Rong-qiao
2016, 31(1): 17-22. doi: 10.13224/j.cnki.jasp.2016.01.003
Abstract PDF(781KB) icon1245 icon534
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A method of improving the ability of low velocity impact resistance of composite material by using the super elastic property of shape memory alloy (SMA) was proposed. Based on the segmented linearization model of SMA and its simplified assumption, SMA super elastic constitutive model was developed by the VUMAT subroutine of ABAQUS. The numerical simulation model of low velocity impact of SMA reinforced composite material was established by ABAQUS to study how SMA absorb and discharge part of deformation energy by using hysteresis damping. Results show that the peak value of impact stress and the deflection of composite material decrease with the increase of SMA volume fraction, but the improvement of the deflection is not obvious at low SMA volume fraction (<10%). With the increase of SMA volume fraction, the impact energy absorption rate of SMA per unit volume decreases, and the SMA fiber has the highest energy absorption rate in the SMA volume fraction of 5%-10%. Numerical result shows that SMA fiber can effectively improve low velocity impact response performance of composite material.
Design on structure of six-component box balance for the aero-engine vector nozzle measuring platform
YU Chang-an, WANG Luo, HE Xian-zhong, QIU Rong-kai, YAO Cheng-wei
2016, 31(1): 23-30. doi: 10.13224/j.cnki.jasp.2016.01.004
Abstract PDF(978KB) icon1282 icon521
Abstract:
In order to meet the high precision measurement needs of aero-engine thrust vector, a compact six-component box balance enabling complete decomposition of thrust vector was developed.The balance was mainly composed of three parts: three-component sensors, fixed frame and floating frame.The elastic component of three-component sensor adopted the form of series-parallel combined structure.The simulation of the sensor's elastic component by using the finite element analysis methods showed each measuring component's sensitivity to its own component loading was much higher than other components, and the support components also preferably cut off the interference among measuring components.This conclusion was also verified by the sensor calibration.Through the stiffness and modal analysis of the six-component box balance, the results prove that the balance doesn't need elastic angle correction and the first order natural frequency of the balance is 218.8Hz, which is superior to the design index 180Hz.The six-component box balance calibration shows that the precision of the balance is lower than 3‰ and the accuracy is lower than 5‰.
Study on mechanical properties of resin composites and models considering temperature environment
SONG Jian, WEN Wei-dong
2016, 31(1): 31-39. doi: 10.13224/j.cnki.jasp.2016.01.005
Abstract PDF(956KB) icon1589 icon614
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The longitudinal tensile, transverse tensile and in-plane shear mechanical properties of T300/QY8911-Ⅳ composites were initially investigated at different temperatures (room temperature,160,200,260℃).The variation rules of modulus and strength as the function of temperature were then discussed, and the corresponding mechanical models were proposed.The test results showed that the longitudinal modulus and strength were less affected by temperature at the range of 200℃. The maximum amplitude was only 2.82% and 1.41%, compared with the average value (room temperature). Due to the resin matrix deterioration, the longitudinal tensile performance was decreased by 5.85% and 7.01% (260℃),respectively. The properties of transverse tensile and in-plane shear were significantly affected by temperature. The modulus of transverse and in-plane shear were reduced by 49.21%,70.34% and the corresponding strengths declined by 38.49%, 44.85% (160℃) with respect to the average modulus (room temperature). The modulus properties mentioned above continued to decline by 25.13%, 38.30% (200℃) and the strength dropped by another 0.41%,15.95%, respectively. The fitting results manifest that the three mechanical models are suitable to fit the data obtained by different temperatures and loads, while the model Ⅱ and Ⅲ are more accurate.
Paths planning of metal rubber blank laying
HUANG Kai, BAI Hong-bai, LU Chun-hong, CAO Feng-li
2016, 31(1): 40-48. doi: 10.13224/j.cnki.jasp.2016.01.006
Abstract PDF(909KB) icon1066 icon490
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Laying metal rubber blank with a pin board was proposed as a preparation technology. An optimization model based on background grids was built. Optimizing methods of dowels and paths planning were established with genetic algorithm according to characteristics of blank laying. Theoretical basis of metal rubber blank laying was provided. Dowel number was obtained according to non-zero grid number of bottom background grids. Dowel configuration was computed with genetic algorithm. Based on the dowel optimization design results, laying paths are devised in each layer. The blank with optimized paths is more homogeneous and denser than that with experiential paths. The advantage of paths planning is more obvious with more laying layers. There is a difference of fifty percent of object function b at ten layers between two kinds of blanks. Layinging quality is little influenced by the number of laying paths in each layer. With increase of helix screw laying length, contact states are coincident in blanks with different numbers of laying paths in each layer.
Nonparametric estimation method of reliability evaluation in competitive fault model
SHEN An-wei, GUO Ji-lian, WANG Zhuo-jian
2016, 31(1): 49-56. doi: 10.13224/j.cnki.jasp.2016.01.007
Abstract PDF(771KB) icon1205 icon502
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The nonparametric estimation method of reliability evaluation was compared and analyzed for the problem of small sample and randomly censoring in the field data of aero-engine. Monte Carlo method was applied and a simulation method was designed to compare the reliability evaluation method within competitive fault model. Through the example of trebling Weilbull distribution, random censoring observations of aero-engine were simulated through this method by comparing four nonparametric estimation methods of reliability evaluation. An example of engineering application was used to illustrate the validity of the method. Results show that the excellence order of nonparametric estimation method is Kaplan-Meier estimation, mean rank order method, Herd-Johnson estimation and Nelson-Aalen estimation under the trebling Weilbull competitive fault model.
Reversible model-simplifying method for aero-engine rotor systems
LU Zhen-yong, CHEN Yu-shu, LI Hong-liang, HOU Lei
2016, 31(1): 57-64. doi: 10.13224/j.cnki.jasp.2016.01.008
Abstract PDF(858KB) icon1304 icon511
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A reversible simplified method was given to investigate the dynamic model for aero-engine high-pressure rotor system. By using the finite element method, the accurate complex dynamics model was built, and also simplified to gain the single-span with dual-disc model and single-disc model based on the center of mass concentration method. The critical whirling speed was compared for the simplified and complex models to indicate the correctness of the simplified method. This modeling-simplify method based on the structural characteristics made low-dimensional nonlinear dynamics analysis and parameter optimization possible with the consideration of the nonlinear factors of supporting, etc. And then the reversibility of the model-simplifying method was investigated. The new complex model and the discs' parameters of equivalent radius, thickness and location were obtained from the single-span with dual-disc model by the principle of optimized centroid location and the total mass of the discs. The 1th to 3th critical whirling speeds of the new complex model and the original model were compared, indicating that the errors were all less than 3%. The reversible model-simplifying method laid the foundation for the multistage-disc's engineering structural parameters design from the simple model structural parameters optimized by the nonlinear dynamics theory.
Optimization algorithm and experiment of a two-disk rotor system
HUANG Jing-jing, ZHENG Long-xi, LIU Gang-qi, MEI Qing
2016, 31(1): 65-71. doi: 10.13224/j.cnki.jasp.2016.01.009
Abstract PDF(864KB) icon1088 icon452
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In order to analyze the performance difference of several optimization algorithms, a model of two-disk rotor system with typical 1-0-1 support scheme was established and the dynamic characteristics were analysed by finite element analysis technology. On this basis, the two-disk rotor system model was integrated to the multidisciplinary design optimization software ISIGHT. The positions of the two disks were selected as the optimization variables, the first order critical speed with the variation range of 10% was set as the constraint, and the optimization objective was to minimize the amplitudes of the two disks crossing the first order critical speed with several different algorithms including evolutionary optimization (EVOL), multi-island genetic algorithm (MIGA), neighborhood cultivation genetic algorithm (NCGA), non-dominated sorting genetic algorithm Ⅱ (NSGA-Ⅱ) and Pointer. The transient experiment was carried out on a high-speed flexible rotor mockup. Experimental results indicated that NSGA-Ⅱ made the two disks' amplitudes decreased 76.94% and 67.42% respectively with the calculation of 240 points. It can be concluded that NSGA-Ⅱ was the best optimization algorithm for the rotor system of this type.
Rotor system's vibration servo control based on magneto-rheological dampers
WANG Kai, HE Li-dong, XING Jian, HU Hang-ling
2016, 31(1): 72-77. doi: 10.13224/j.cnki.jasp.2016.01.010
Abstract PDF(781KB) icon1252 icon539
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In order to solve the problem of too large rotating machinery vibration around the critical speed, a rotor system test bench was established. Without changing the original supports of the rotors system, one magneto-rheological damper was installed onto each shaft. Different working conditions were set to study the influences of the magneto-rheological dampers on rotor system's vibration. The results showed that the magneto-rheological damper could reduce the vibration of the rotor system near the critical speed, and the decreasing amplitude was 90%. According to the test results, a servo control strategy based on vibration amplitude feedback of rotor was proposed to control the rotor vibration amplitude, which could follow the vibration amplitude, change the current of magneto-rheological damper according to the vibration amplitude to control the rotor system's vibration on line. The results show that the servo control method can adjust the current varying with rotor system's vibration in real time, and make the amplitude stay stable around the target value, so as to achieve the auto control of rotor system vibration.
Simulation and failure analysis of aircraft engine's bleed valve mechanism based on virtual prototyping technology
XIE Meng-tao, LU Shan, CHEN Yang-hui
2016, 31(1): 78-83. doi: 10.13224/j.cnki.jasp.2016.01.011
Abstract PDF(846KB) icon1012 icon573
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For many rocker fractures of a certain type of aircraft engine's bleed valve mechanism, a dynamic model of the mechanism was built in order to obtain the fault reason and reduce the time and cost of the troubleshooting. The fault recurrence of the mechanism was implemented based on virtual prototyping technology by ADAMS and ANSYS software. The influence factor and law of fractured component's stress was found out, and the fatigue life of some stress levels was estimated. Finally, improvement proposals for increasing the gap B to 0.273mm and 0.279mm to ensure the rocker's shortest life and whole life were given respectively. Thus, the basis for the troubleshooting in engineering was provided.
Experiment on effect of pressure-side winglet on flow field in turbine cascade at different tip clearances
ZHONG Jing-jun, WEI Man, LU Hua-wei
2016, 31(1): 84-91. doi: 10.13224/j.cnki.jasp.2016.01.012
Abstract PDF(980KB) icon1113 icon463
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Detailed experiments were carried out to investigate the effect of the tip clearance flow in a turbine cascade with different width pressure-side winglets.The flow field of the cascade outlet and the static pressure distribution on the blade surface were surveyed in detail at different tip clearance height of 0.5%h, 1%h, 1.5%h.The results show that, as the tip clearance height increases, the leakage flow is intensified, the leakage vortex is strengthened, the total loss of cascade is increased, and the up channel vortex is weakened.Pressure-side winglet has a good effect at the 0.5%h tip clearance height, the total loss of the cascade is reduced by 18% with width being 0.4 times of the local blade thickness.0.3 times of the local blade thickness case reduces the total loss of the cascade by 10.37% at the 1%h tip clearance height.At the 1.5%h tip clearance height, the pressure-side winglet almost has no effect on clearance leakage flow, but reduces the total loss of the cascade to a certain extent.
Application of Pareto multi-objective algorithm in centrifugal compressor volute optimization
WU Ya-dong, CAO An-guo, LIU Peng-yin, DU Zhao-hui
2016, 31(1): 92-99. doi: 10.13224/j.cnki.jasp.2016.01.013
Abstract PDF(960KB) icon1236 icon481
Abstract:
A centrifugal compressor aerodynamic optimization system based on Pareto multi-objective algorithm was established.The system integrated the parameterized geometric model, ICEM(integrated computer engineering and manufacturing) mesh generation, CFX(computational fluid dynamics X) computation and CFD combined optimization technique.Using this system, the optimization was implemented for a centrifugal compressor volute, and the total pressure loss coefficient and static pressure recovery coefficient were chosen as target variables.Compared with prototype design, the average total pressure loss coefficient of optimal design decreased by 11.79% and the average static pressure recovery coefficient increased by 16.97%.Meanwhile, the secondary flow inside the volute was reduced to a certain degree, and the volute matched better with the impeller.The results show that the multi-objective optimization system is effective to the performance of the centrifugal compressor.
Influence of blade untwist on transonic high bypass ratio fan performance
YANG Hui, SHEN Zhen, ZHENG Yun
2016, 31(1): 100-105. doi: 10.13224/j.cnki.jasp.2016.01.014
Abstract PDF(872KB) icon1086 icon518
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Influence of blade untwist on transonic high bypass ratio fan performance were studied using the software based on the fluid-solid coupling algorithm, considering the nonlinear effects of unsteady aerodynamic force on the blade deformation. Firstly, the deformation induced by centrifugal force was calculated starting from the cold blade shape, and then the deformation induced by unsteady aerodynamic force was obtained using the fluid-solid coupling software. The effect of the dynamic blade deformation on aerodynamic performance of the high bypass ratio fan was investigated at three rotation speeds. Results show that changes of the shock position on the blade surface have significant influence on the blade untwist angle under the transonic conditions. In the rotation speed range concerned, the calculated mass flow rate by the designed blade shape is greater than that by the dynamic one up to 7%, which causes the engine takeoff thrust less than the predicted value. The results also indicate that the accurate blade shape is important for predicting aerodynamic performance during the design stage.
Numerical simulation of the effects of trailing edge thickness on aerodynamic performance of low pressure turbine
LI Chao, YAN Pei-gang, HAN Wan-jin, WANG Qing-chao, HAN Wan-long
2016, 31(1): 106-114. doi: 10.13224/j.cnki.jasp.2016.01.015
Abstract PDF(1026KB) icon1223 icon470
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Numerical simulation method was used to study the effects of trailing edge thickness on aerodynamic performance of Pak-B low pressure turbine. The trailing edge thickness was increased to control the boundary layer separation and reduce losses of low pressure turbine,and the flow control mechanism of increasing the trailing edge thickness was also revealed. It was shown that appropriate increasing trailing edge thickness could decrease the energy loss of low pressure turbine and increase the turning angle. Appropriate increasing trailing edge thickness could decrease the energy loss coefficient based on inlet velocity by 10.4%, increase the turning angle by 1.73% for Reynolds number of 25000 and free stream turbulence intensity of 1%. Appropriate increasing the trailing edge thickness and pitch also could reduce the energy loss coefficient based on inlet velocity, increase the turning angle. When the trailing edge thickness increased to 4%s and the pitch increased by 2.2%, the energy loss coefficient based on inlet velocity decreased by 7.4% and the turning angle increased by 1.25% for Reynolds number of 25000 and free stream turbulence intensity of 1%. Increasing the thickness of trailing edge can be used to develop low solidity and highly loaded low pressure turbine cascade.
A RANS-based prediction method for the airfoil broadband trailing edge noise
BAI Bao-hong, LI Xiao-dong
2016, 31(1): 115-123. doi: 10.13224/j.cnki.jasp.2016.01.016
Abstract PDF(982KB) icon1035 icon464
Abstract:
A RANS (Reynolds averaged Navier-Stokes)-based prediction method for the airfoil turbulent boundary layer trailing edge noise was developed. The Navier-Stokes equations were firstly reformulated to the form that the left hand side was a linear wave propagation operator and the right hand side was the source term that consists of Reynolds stresses. To reduce the computation time and avoid the spatial singularity of the Green function, the adjoint Green functions method was employed to compute the exact or ‘tailored’ Green functions; moreover, the source term was generated by the RANS-based modeling method. Application of the present method on the broadband trailing edge noise of NACA0012 airfoil was made to validate the present method. The OpenFOAM solver was applied into the mean flow computation of NACA0012 airfoil and the Green function for semi-infinite flat plate under uniform mean flow was used to approximate that of thin airfoil. The predicted spectrum of the broadband trailing edge noise indicates that: for various incoming flow velocity and angle of attack, the current method can not only predict the amplitude and the peak frequency accurately, but also the whole spectra is in good agreement with the current available experiment data (±3dB), which demonstrates the accuracy and applicability of the method.
Numerical investigation of stall mechanism for transonic tandem rotor
SONG Ming-zhe, YUAN Wei, LI Shao-bin
2016, 31(1): 124-135. doi: 10.13224/j.cnki.jasp.2016.01.017
Abstract PDF(1617KB) icon1090 icon533
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In order to enhance the stall margin of transonic tandem rotor, a better understanding about its flow structure and stall mechanism is required. Thus, a high-loaded transonic tandem rotor was designed to perform a loading coefficient of 0.56 at tip tangent speed of 450m/s. Based on the simulation results, firstly, the tip flow field and stall mechanism of this tandem rotor with the shroud gap of 0.5mm was analyzed, and then the influence of different tip clearances and percent pitch values on stall mechanism was studied. It is indicated that the tip area of forward blade plays a prominent role in the stability of transonic tandem rotor. Along with the increase of tip clearance, the stall mechanism of tandem rotor also changes from the stagnation of aft blade tip area caused by wake and subsurface flow to the blocking of forward blade tip area caused by the tip leakage flow. The tandem rotor will achieve its best effect under high percent pitch(PP) value, and the stall onset position will move from the aft blade towards the forward blade with the increase of percent pitch.
Numerical study on the influence of some factors on results accuracy in rotor aerodynamic simulation
YE Liang, ZHANG Ying, ZHU Xing-lin, YANG Shuo
2016, 31(1): 136-142. doi: 10.13224/j.cnki.jasp.2016.01.018
Abstract PDF(874KB) icon1205 icon502
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Numerical analysis for evaluating the effect of some common factors on rotor aerodynamics was conducted with an in-house CFD solver, in which a second-order upwind finite-volume and dual time-stepping scheme were used for Navier-Stokes equations discretization under an embedded grid system; and the numerical process was accelerated by OMP parallel technique.The involved problems mainly include the effect of background grid points scale on tip-vortex capture in hover, shock wave in forward flight and blade force, and the differences between the aerodynamics results obtained with/without 1D momentum far field boundary condition.The calculated rotor lift and torque discrepancy in hover are approximately 6% and 2.6% with different background grid points, and the drag and torque discrepancy in forward flight are 2.58% and 3.28% separately. The lift results show about 3%-5% difference with and without 1D momentum far field boundary condition correction.The fluctuation range of rotor aerodynamics with above-mentioned parameters was given by calculation, providing useful reference in rotor aerodynamics simulation.
Analyses on inhibiting of transonic characteristics of rotor with new type blade-tip
ZHAO Guo-qing, ZHAO Qi-jun, WU Qi, WANG Bo
2016, 31(1): 143-152. doi: 10.13224/j.cnki.jasp.2016.01.019
Abstract PDF(1751KB) icon1105 icon438
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To investigate effects of different new type blade tips on transonic characteristics of helicopter rotor, numerical analyses about the impacts of blade tips on the local flow details and aerodynamic characteristics near blade-tip were carried out. A high-precision CFD method was developed with a highly-efficient embedded grid method for the simulation of the rotor flowfield. Based on these methods, the influences of shape of blade tip on the intensity of shock wave, shock-boundary layer interference, blade tip wake and aerodynamic performance of rotor were analyzed at a transonic state respectively. The numerical results indicate that backward sweep and dihedral shape of blade tip have a smaller effect on reducing the transonic characteristics of rotor, but forward sweep and anhedral shape of blade tip can effectively reduce the transonic region, the intensity of shock wave and flow separation induced by the shock-boundary layer interference. Furthermore, sweepback blade-tip has a remarkable effect in reducing rotor torque, and straight forward sweep blade-tip can effectively reduce rotor torque (12.3% reduction of rotor torque for the case of straight forward sweep 30°) at larger rotor disc loading state, and anhedral blade-tip can effectively inhibit the blade tip vortex intensity (50% reduction of vorticity magnitude of blade-tip vortex for the case of anhedral 30°) and accelerate the dissipation of blade-tip vortex wake.
Algorithms for hypersonic fluid-structural-thermal integrated
JI Wei-dong, WANG Jiang-feng, FAN Xiao-feng, ZHAO Fa-ming
2016, 31(1): 153-160. doi: 10.13224/j.cnki.jasp.2016.01.020
Abstract PDF(912KB) icon1170 icon547
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An fluid-structural-thermal integrated algorithm was presented based on detailed discussion about the deficiency in domestic and foreign study on algorithm of fluid-structural-thermal integrated. A unified integral equation system was developed as the control equation for physical process of aero-heating and structural heat transfer. The whole physical field was discretized by using an up-wind finite volume method. The corresponding algorithm were given to work out the value of the temperature, the temperature gradient and the heat transfer coefficient on the boundary between fluid and structure. In terms of time step, a multi-step Runge-Kutta iteration scheme was used in steady states while a dual-time step method was adopted in unsteady states. Numerical simulation of the aero-heating and structural heat transfer problem on a two-dimensional circular tube model was performed. Results show that the 2s stagnation surface temperature is 390K. Compared with other papers, the maximum absolute error is 3.1K. The steady state stagnation surface temperature is 647K.
Analysis on aerodynamic characteristics of fan-in-wing configuration of V/STOL aircrafts
WANG Hong-bo, ZHU Xiao-ping, ZHOU Zhou, GAN Wen-biao, ZHANG Le
2016, 31(1): 161-167. doi: 10.13224/j.cnki.jasp.2016.01.021
Abstract PDF(829KB) icon1254 icon536
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The complex flow caused by the interaction of the fan jets with the freestream was numerically simulated and compared using computational fluid dynamics(CFD) method based on structured/unstructured mixed grids in order to investigate aerodynamic characteristic of a fan-in-wing configuration about vertical/short takeoff and landing(V/STOL) under transition. The ducted propeller of NASA was simulated firstly using sliding mesh technique. Time-averaged results showed a good agreement with experiments and the relative error was 5.3%, proving the CFD methods using above was reliable and accurate. And then, the aerodynamics of fan-in-wing configuration with different attack angles was calculated. Results indicate that the special effects of suckdown and blocking caused by the fan jets lead to notable lift and drag increments, the max lift increment is 2.6 times the closed-wing's lift and the max drag increment is 3.2 times the closed-wing's drag. The mixed flow field located at the rear of the wing results in a little of lift loss and rolls up in a pair of vortices.
Effect of concave groove on the stability of boundary layer
LIU Kai-ping, LUO Ji-sheng
2016, 31(1): 168-178. doi: 10.13224/j.cnki.jasp.2016.01.022
Abstract PDF(1170KB) icon1191 icon495
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In order to predict the transition position using eN method for flat boundary layer with concave groove, the effects of concave groove on the evolution of disturbance in supersonic boundary layer with Mach number of 4.5 were studied by numerical simulation and flow stability method. The amplitude and growth rate distribution along the flow direction with two sizes of concave groove was revealed. The results show that the range of effect of concave groove on the basic flow is only limited in the concave groove and near range. Concave groove has a suppressed effect on the evolution of disturbance to some extent, the bigger size means the more obvious inhibitory effect. After concave groove, the effect of concave groove on the growth rate of disturbance amplitude is little, and relative variation is smaller than 2%.At the same time, the position of transition can be predicted more accurately with a smaller concave groove by eN method combined with stability analysis and a correction factor of N.
Experiment on emissions of a trapped vortex combustor with different bluff body widths
WU Ze-jun, HE Xiao-min, JIN Yi, SONG Yao-yu, HONG Liang, XUE Chong
2016, 31(1): 179-187. doi: 10.13224/j.cnki.jasp.2016.01.023
Abstract PDF(834KB) icon1229 icon481
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To reveal the effects of air flow-rate distribution on emission characteristics of trapped vortex combustor and understand the generating processes of emissions as well as the factors affecting the processes, a trapped vortex combustor with different centric bluff body width was designed. And the combustor was designed to be fueled only in cavity. Emission experiment was conducted at atmospheric pressure. And inlet temperature of the combustor was kept at 200℃. Inlet Mach number varied from 0.15 to 0.3.Atomization quality, cavity equivalence ratio in combustion zone, and inlet Mach number and residence time influenced emissions in combustors. Generally, improvement of atomization quality and increase of cavity equivalence ratio can enhance combustion process and consequently reduce emissions of CO and HC. However, it will also lead to increase of NOx emission. As cavity equivalence ratio is relatively lower, CO emission curves decline gradually, and even ascend in some cases. HC emission curves descend rapidly here. This is mainly because the consumption of HC is much faster than CO. When cavity equivalence ratio is increasing, the fueling pressure is elevated and thus atomization is enhanced, so vaporizing time of fuel spray is shortened. This will result in rapid decline of HC emission. Although, a large amount of CO will be produced and there is no enough time to consume. CO emission declines rapidly when cavity equivalence ratio is high enough because of the higher temperature in the combustion zones. In gas turbine combustors, the producing and consuming process of NOx is very complicated, and there is no enough data to demonstrate it. Comparison between different bluff body widths has been made as the cavity air flow-rate on front wall are similar. And it reveals that the emissions of CO and HC are mainly determined by the cavity condition. However, NOx emission is also impacted by the mainstream.
Research on n-decane as surrogate fuel of aviation kerosene in atomization process
HUO Wei-ye, LIN Yu-zhen, ZHANG Chi, ZHUANG Chun-qing
2016, 31(1): 188-195. doi: 10.13224/j.cnki.jasp.2016.01.024
Abstract PDF(812KB) icon1224 icon493
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Atomization characteristics of aviation kerosene RP-3 and single component hydrocarbon fuel n-decane were tested to study the feasibility of n-decane as an atomization surrogate fuel of aviation kerosene in component testing stage.Results showed that, at room temperature, atomization Sauter mean diameter (SMD) located at igniter orifice of the two fuels was measured using Malvern laser particle size measurement system when the air pressure drop through the swirler was 0, 500, 2000Pa, and the fuel pressure varied from 0.1MPa to 1.0MPa by 0.1MPa uniformly.SMD of the two fuels decreased slowly when fuel pressure increased to more than 0.5MPa, showing that atomization process of the two fuels basically completed, and the atomization SMD was between 30-45μm.When the air pressure drop was the same, the atomization SMD of n-decane was slightly larger than that of aviation kerosene due to the slightly larger viscosity and surface tension.When the fuel pressure was more than 0.5MPa, physical properties of the fuels and aerodynamic force around the atomization could be ignored, and the atomization SMD of the two fuels was very close.Further, the experimental data were analyzed and fitted to obtain the empirical relationship of atomization SMD of the two fuels in swirl flow.The relative difference of the fit coefficients was about 7%, so, n-decane could be used as the physical surrogate fuel of aviation kerosene atomization after appropriate correction.
Influences of geometric parameters on leakages and bristle tip forces in brush seals
HUANG Shou-qing, SUO Shuang-fu, LI Yong-jian, WANG Yu-ming
2016, 31(1): 196-202. doi: 10.13224/j.cnki.jasp.2016.01.025
Abstract PDF(855KB) icon992 icon408
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Based on a type of three-dimensional slice model of brush seals in combination with the CFD method, the aerodynamic forces applied onto bristles were analyzed and simplified to the concentration of a smaller amount of point forces. Bristle tip forces and torques caused by aerodynamic forces were quantitatively investigated using torque rebalance and linear superposition principles. A test rig and a brush seal ring were applied to verify the related theory in test. Orthogonal tests were used to study the influences of the bristle length, inter-bristle spacing, bristle row number, lay angle, bristle diameter and protection clearance on leakage rates, aerodynamic forces, bristle tip forces and torques. Results indicate that the calculated total leakage rate and torques agree with the test data, the error at each point is less than 20%. The influences of bristle diameter, inter-bristle spacing, protection clearance, bristle row number on total leakage rate are very significant, and influence of the lay angle on torques are very significant too.
Influences of side load and heating orientation on critical heat flux in a rectangular groove
LI Gang, SONG Bao-yin, ZHANG Zhao, WANG Hong, SONG Jun-hui
2016, 31(1): 203-210. doi: 10.13224/j.cnki.jasp.2016.01.026
Abstract PDF(838KB) icon1013 icon433
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An experimental investigation into the effects of side load and heating orientation on the critical heat flux of flow boiling in a narrow rectangular groove was performed with a rotational platform. Using distilled water as working fluid, the change trend of mass velocity, the pressure drop in test section and its outlet wall temperature before and after reaching critical heat flux were obtained, the effects of side load and heating orientation on critical heat flux were investigated at different mass velocities, inlet temperatures, dynamic loads and heating orientations. Flow instability was briefly analyzed. The results show that in addition to the rapid wall temperature rise, the effective heat flux decreases as the critical heat transfer occurs. The pressure drop in test section decreases and mass velocity rebounds obviously after power cutoff. The effects of side load and heating orientation on critical heat flux are obvious. Not soon before and after the critical heat transfer occurs, the back flowing vapor increases the inlet fluid temperature, thus enhancing the flow instability.
Numerical analysis on effect on injection for supersonic combustor pylon
WANG Ying-yang, LI Xu-chang, WANG Hong-yu, ZHANG Han
2016, 31(1): 211-218. doi: 10.13224/j.cnki.jasp.2016.01.027
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Abstract:
To analyze of flow characteristics of the pylon before/after injection in supersonic combustion,the numerical simulation was carried out to investigate the effect rules of pylon on ethylene injection cold flow field.The influence of several conditions on flow field was contrastive analyzed,such as: with and without pylon, different injection locations and different injection angles. It is found that the streamwise vortex zone and low pressure depression behind the pylon are the paramount mechanism for mixing enhancement. Further distance between the pylon and injector is good for mixing enhancement for stronger wise vortex zone, but leads to higher total pressure loss for less low pressure depression. Moreover, injection with the distance between pylon and injector of 2.2d, injection angle of 90 degree is recommended regarding high mixing efficiency and less total pressure loss.
Denoising method based on dual-tree complex wavelet transform and MCA and its application in gear fault diagnosis
XU Yong-gang, ZHAO Guo-liang, MA Chao-yong, HOU Shao-fei
2016, 31(1): 219-226. doi: 10.13224/j.cnki.jasp.2016.01.028
Abstract PDF(956KB) icon982 icon471
Abstract:
The vibration signals of gearbox incipient failure often contain strong noise, which results difficulty in fault feature extraction by the conventional denoising method, such as threshold based method.Thus, a new method based on dual-tree complex wavelet transform (DT-CWT) and morphological component analysis (MCA) was proposed.In the processing, the signal was firstly processed by DT-CWT to gain the coefficients of different layers.Secondly, MCA was employed to denoise the coefficient which was more periodic.Then, the denoised signal with weak fault feature could be gotten from a following single reconstruction.Finally, the fault characteristic frequency could be located accurately by simple envelope spectrum analysis.A simulate signal and incipient failure vibration signal of mill gearbox were processed using this method, and the results show that the method can remove the strong background noise in the signal effectively, and has better effect than single MCA and soft threshold method, and get a more clear fault characteristic frequency, thereby providing a new method for gearbox incipient fault diagnosis.
Design for straight bevel gear based on low installation error sensitivity and experiment tests
CAO Xue-mei, SUN Ning, DEND Xiao-zhong
2016, 31(1): 227-232. doi: 10.13224/j.cnki.jasp.2016.01.029
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Abstract:
Modified tooth surfaces of one of the members of the straight bevel gear set were proposed in order to low the installation error sensitivity and improve the stability of contact patterns. Profile modification was carried out by changing the trajectory of the cutter from line to parabolic; tooth trace modification was carried by changing the roll, so the modifield tooth surface with drum shape could be obtained and the gear set could mesh with point contact. In order to further improve the meshing stability, the optimization model for tooth surface modification was proposed. The two modification coefficients were used as optimal variables; the Gauss curvatures of two meshing surfaces at contact points were controlled to construct the objective function, and the principal curvatures of the ease-off tooth surface at the contact point were controlled to ensure that the length of the instantaneous contact ellipse is at least 1/3 of tooth width. Finally numerical example of design of straight bevel gear drives was included to illustrate the advantages of the proposed geometry. A cutting and rolling experiments validate that the patterns maintain good stability with amount of the total axial misalignment and total axial separation accounted for 30% of the normal module.
Thermal elastohydrodynamic lubrication analysis of aero-engine mainshaft ball bearing based on quasi-dynamic
SHI Xiu-jiang, WANG Li-qin, GU Le, ZHENG De-zhi, ZHAO Xiao-li
2016, 31(1): 233-240. doi: 10.13224/j.cnki.jasp.2016.01.030
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Abstract:
Taking aero-engine mainshaft ball bearing under typical high speed and load conditions as cases, the motion and loaded states of micro-contact region were obtained based on quasi-dynamic analysis, and the minimum film thickness(MFT) was estimated with Hamrock-Dowson(H-D) formula and ZHAI Wenjie thermal modified formula; meanwhile, the MFT under various conditions was acquired through thermal elastohydrodynamic lubrication(EHL) analysis. Comparing the MFT of experiment testing, H-D, ZHAI Wenjie and numerical analysis, the EHL status was ensured by film thickness ratio. Results indicate that H-D and ZHAI Wenjie's MFT have large difference with experiment results, but numerical analysis shows a well agreement with experiment data and the error is within 10%.The operating condition effects on EHL property were discussed. Results indicate the global film pressure increases and the thickness decreases in the presence of radial load; the film pressure decreases and the thickness increases with the increase of speed, but the trend becomes slower.
Prediction on self-excited vibration of thin spur gear based on energy method
YANG Long, WANG Yan-rong
2016, 31(1): 241-248. doi: 10.13224/j.cnki.jasp.2016.01.031
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Abstract:
The fatigue failures caused by the vibration often happen in the gears of the aero-engines, so it is urgently necessary to analyze the cause of the vibration. The self-excited vibration of the thin spur gear was studied based on the energy method and a theoretical method used to predict the self-excited vibration was proposed. The expressions of the excitation work and damping work to the travelling wave vibration of the gear were derived. By analyzing the change of the system energy, the likelihood of the occurrence of the self-excited vibration for the thin spur gear was verified in theory, while the condition and gear load in occurrence of the self-excited vibration were also determined. Through the numerical simulation, the influences of the contact ratio, nodal diameter and damping ratio on the stability of the self-excited vibration were studied. Results show that the self-excited vibration will occur in the backward travelling wave of the driven gear and the forward travelling wave of the driving gear in the underdamped situation. For the same conditions, the self-excited vibration is more easily to occur in low nodal diameters vibration mode.
Numerical calculation of aero-engine model based on self-tuning Broyden quasi-Newton method
WANG Yuan, LI Qiu-hong, HUANG Xiang-hua
2016, 31(1): 249-256. doi: 10.13224/j.cnki.jasp.2016.01.032
Abstract PDF(738KB) icon1010 icon410
Abstract:
A self-tuning Broyden quasi-Newton method combined with computing divergence mechanism judging and tuning was proposed. By combining the quadratic convergence of Newton-Raphson method and the super-linear convergence of Broyden quasi-Newton method, the proposed method had higher computing performance in calculation of nonlinear system. Targeting variable cycle engine component-level model, the steady state and dynamic simulation have been calculated by Newton-Raphson method, Broyden quasi-Newton method and the self-tuning Broyden quasi-Newton method. Results shows that, the self-tuning Broyden quasi-Newton method has greater adaptability, faster calculation speed and stronger convergence. The component computing times of the self-tuning Broyden quasi-Newton method is 15% of the Newton-Raphson method in dynamic simulation, the dynamic error is lower than 15% of the Broyden quasi-Newton method and 28% of the Newton-Raphson method, the maximum amount of residual is lower than 25% of other methods. These results prove the self-tuning Broyden quasi-Newton method superiority, the objective of the proposed method has been achieved.

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