2019 Vol. 34, No. 1

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Start-up and heat transfer performance of a sodium-potassium alloy heat pipe under different conditions of heating power
2019, 34(1): 1-7. doi: 10.13224/j.cnki.jasp.2019.01.001
Abstract PDF(1024KB) icon1099 icon1234
Abstract:
A sodium-potassium ally (45-wt.%-Na and 55-wt.%-K) heat pipe was experimentally tested to investigate the effect of heating powers (800, 1000, 1200, 1400, and 1600W) on start-up and heat transfer performances. The results showed that under the tested operation conditions, the sodium-potassium ally heat pipe presented an optimal start-up performance with the heating power. Within the range of 800-1600W of heating power, the heat pipe could achieve a dynamic equilibrium state of heat transfer as the heat was carried away by cooling water in time, and the heat transfer coefficient of the sodium-potassium ally heat pipe, convective heat transfer coefficients of evaporator and condenser sections almost linearly increased with the heating power.
Aero-engine exhaust gas temperature prediction model based on IFOA-GRNN
2019, 34(1): 8-17. doi: 10.13224/j.cnki.jasp.2019.01.002
Abstract PDF(1000KB) icon1329 icon930
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General regression neural network (GRNN) has a good nonlinear mapping ability.So exhaust gas temperature (EGT) is predicted by GRNN.But, its accuracy of prediction is affected by the width coefficient of GRNN.To address the problem,the GRNN optimized by the improved fruit fly optimization algorithm (IFOA-GRNN) was proposed. And it was used to predict EGT.Taking the engine as an example, some parameters were taken as input variables and EGT taken as output variable of prediction models.The forecast results of IFOA-GRNN, FOA-GRNN(fruit fly optimization algorithm to optimize GRNN), GRNN,auto-regressive and optimized support vector regression were compared under the same training samples and testing samples.The experiment results showed that the convergence accuracy of IFOA-GRNN was higher than FOA-GRNN. Average relative error of IFOA-GRNN for EGT prediction was 2.47%,and the goodness of fit was 0.8506, the prediction effect of IFOA-GRNN was better than other comparison algorithms.And it was more accurate than other methods in the prediction of aero-engine exhaust gas temperature under noisy and no-noise conditions.
Influence of group-hole nozzles on spray and combustion of an opposed piston opposed cylinder diesel engine
2019, 34(1): 18-26. doi: 10.13224/j.cnki.jasp.2019.01.003
Abstract PDF(1095KB) icon1045 icon789
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With focus on the difficulty of mixture formation of an opposed piston opposed cylinder diesel engine, CONVEGE CFD software was employed to establish the numerical simulation model of an opposed piston opposed cylinder diesel engine. Three arrangements of the converging group-hole nozzle were designed,and without modifying the injection pressure,the fuel spray, mixture formation and combustion process of an opposed piston opposed cylinder diesel engine model were analyzed. The results indicated that the group-hole nozzle had negligible influences on spray penetration distance compared with conventional nozzle. The group-hole nozzle was helpful in improving the in-cylinder turbulence kinetic energy and accelerating the air-fuel mixing rate. Meanwhile, the mixture was evenly distributed and widely spread, helping to improve the quality of mixture and increase the in-cylinder pressure and combustion efficiency as well as improve the engine performance. Among three designs, the indicated power of the engine with the third pattern of converging group-hole increased by 7.6%.
Experiment of grid-generated turbulent ina smooth channel
2019, 34(1): 27-33. doi: 10.13224/j.cnki.jasp.2019.01.004
Abstract PDF(640KB) icon874 icon875
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In order to simulate the flow and heat transfer in a turbine coolant channel, grids were used to control the turbulent intensity in a smooth channel. Different sizes of grids were used to generate different turbulence intensity. In the experiment, three different kinds of grids were put in a square smooth channel with the cross-section of 80mm×80mm. Hot-wire was used to measure the turbulence with Reynolds ranging from 5000 to 30000. The results showed that after flowing through the grids, the turbulent intensity can be up to 4.5%, and decreased along the stream-wise directions. The effect of Reynolds numbers on turbulent intensity is not obvious in the current work. And the turbulent integral time scale has a positive relationship with Reynolds numbers.
Design and application of an air-cooled probe for total pressure measurement at combustor outlet
LIU Xupeng, SUN Qi, WANG Xiaoliang, XUE Xiusheng, YIN Dong
2019, 34(1): 34-44. doi: 10.13224/j.cnki.jasp.2019.01.005
Abstract PDF(600KB) icon771 icon819
Abstract:
An air-cooled probe was designed for measurement of total pressure at combustor outlet; its cooling scheme combined the film cooling and convection cooling. With the aid of CFD technique, cooling effectiveness of the coolant jets at various blow ratios was compared; suitable blow ratios and configuration of film holes were chosen accordingly. The overall cooling performance of the probe was evaluated via CFD technique, the design was improved according to the simulation result, and the cooling effect of the leading edge was obviously strengthened by increasing the local coolant mass flow rate. The results of wind tunnel test indicated that, between Mach numbers 0.2 and 0.4, the probe achieved a high accuracy at various attack angles. The probe was utilized in an annular combustor rig test, the highest temperature reached 1760K and total pressure reaches 1036kPa. The result of rig test demonstrates that the coolant film distribution consistent appropriately with the CFD results.
Experiment of discharge coefficient of counter inlet effusion cooling holes with compound angle
2019, 34(1): 45-50. doi: 10.13224/j.cnki.jasp.2019.01.006
Abstract PDF(578KB) icon1052 icon802
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The flow direction of air in the outer annulus passage of reverse-flow combustors was opposite to the flow direction of fuel gas. The discharge coefficient of compound angle effusion cooling holes was investigated under this condition. The investigation focused on how the discharge coefficient varied with inclined angles (25°-55°), orientated angles (90°-180°) and pressure drop coefficient. The results showed that the discharge coefficient of the effusion hole with compound angle increased with the increase of inclined angles, but decreased with the increase of the orientated angles. The discharge coefficient presented approximately linear rise with the increase of pressure drop coefficient first, and then grew nonlinearly when pressure drop coefficient was close to 0.95.
Numerical study on the two-wave transition process in rotating detonation combustor under separate injection condition
2019, 34(1): 51-62. doi: 10.13224/j.cnki.jasp.2019.01.007
Abstract PDF(1448KB) icon816 icon825
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In order to analyze the flow field structure of the two-waves evolution in the rotating detonation engine, a numerical simulation was conducted to investigate the formation process of two detonation waves under the separate injection condition. The results showed that from ignition to stable detonation, three phases including ignition phase, collision phase and stable phase, were included in the process. The first collision happened in two detonation waves, but two pressure waves were formed due to lack of fresh mixed gas around the collision zone. Then, the second collision happened in two pressure waves.As a result,the detonation wave and shock wave were formed due to the existence of mixed gas around the second collision zone. After the second collision, a high pressure zone was formed due to the pressure wave reflection and overlay, then the gas was compressed by the high pressure zone and the temperature of the gas was increased, the high temperature gas ignited the fresh mixed gas, finally, the second detonation wave was formed. When the detonation wave was stable, the wave pressure reached 1.45MPa, the temperature was 2500K, and the velocity was 1738m/s. Besides, the thrust on the outlet was 79.76N and the specific impulse was 2312.15s.A significant fluctuation was created by oblique shock wave on the outlet.
Experiment on spray characteristics of air-assisted injection under flash boiling conditions
2019, 34(1): 63-72. doi: 10.13224/j.cnki.jasp.2019.01.008
Abstract PDF(1178KB) icon794 icon832
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The effects of ambient pressure and fuel temperature on spray characteristics of air-assisted injection system were investigated by using high-speed photography and phase Doppler particle analyzer (PDPA) in a constant volume chamber. The ambient pressure ranged from 0.01MPa to 0.1MPa, and the fuel temperature ranged from 25℃ to 100℃ during the experiment. The experimental results showed that spray condition transferred from the non-flash boiling to flash boiling gradually with the decrease of the ambient pressure that induced the intensified bubble bursting at the nozzle exit. When the ambient pressure was less than 0.02MPa, the spray was in flash boiling condition, bringing about the increase of the droplet velocity, the decrease of the droplet diameter and the spray expansion in the near field. Meanwhile, the rising fuel temperature led to the decrease of the fuel surface tension, which can accelerate the break of the droplet. As the fuel temperature reached 100℃, when the spray was in flash boiling condition, the spray expansion occurred in the far field.
Numerical and experimental study based on reverse jet to suppress leakage flow in the labyrinth seal
2019, 34(1): 73-83. doi: 10.13224/j.cnki.jasp.2019.01.009
Abstract PDF(1502KB) icon909 icon825
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Two-dimensional numerical simulations were performed for a straight labyrinth seal passage, nine kinds of sealing structure model were established, the effects of reverse jets at different positions and angles on the internal flow field of the labyrinth were studied emphatically, and the relationship between the front and back pressure ratio of the labyrinth and the leakage coefficient under different models was discussed. The results show that all different jet positions and angles can enhance the seal effect of labyrinth seal, the smaller jet angle, means the better sealing effect, when the jet position was in the middle of the first section of the tooth cavity, the leakage effect was the best. When the jet angle θ was 45 ° and the jet position was in the middle of the first tooth cavity, the leakage coefficient can be reduced by 11.5% corresponding to the case without reverse jets. On the basis of numerical simulation, a two-dimensional straight labyrinth seal experiment with reverse jet was proceeded, using PIV to obtain the flow field with reverser jet under three jet angles and three jet positions, the experimental results were consistent with the calculated variation law.
Numerical study on influence of pre-swirl nozzle radial angles on pre-swirl characteristic
2019, 34(1): 84-91. doi: 10.13224/j.cnki.jasp.2019.01.010
Abstract PDF(886KB) icon884 icon882
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To reduce the aerodynamic loss in a low position pre-swirl system, numerical simulations were carried out to study the flow characteristics, temperature drop and specific entropy increment for pre-swirl system with nozzles radial angles from 0° to 30°. The results showed that non-dimensional temperature drop increased firstly and then decreased, and flow resistance reduced with the increasing pre-swirl nozzle radial angle bringing about the increase of mass flow rate. The non-dimensional temperature drop of pre-swirl system nozzles with radial angle most increased 18.3% than traditional nozzles when rotational Reynolds number was 2.3×107, and there was a certain angle that could lead to the best characteristics of temperature drop. The dissipative loss of the pre-swirl system mainly occurred in the pre-swirl cavity and the rotating cavity, making up 42.4% and 30.2% of the total specific entropy increment respectively when nozzles radial angle was 10°. It could improve the flow effects in pre-swirl cavity and reduce the loss of pre-swirl system if the nozzles radial angle was designed properly.
Fatigue life prediction method based on the features of surface defects
2019, 34(1): 92-98. doi: 10.13224/j.cnki.jasp.2019.01.011
Abstract PDF(767KB) icon821 icon824
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On the basis of fatigue data of specimen with surface defects, the size parameter of surface defects was proposed, and introduced into the Walker life equation to study the effect of size of surface defects. And the life prediction results of the equation were compared with the calculation results of life prediction method considering the stress gradient. The scatter bands of the results of two models were within ±3, indicating that the method is reliable. Then the equation was used in predicting the fatigue life of powder metallurgy turbine disk and obtaining the influence law of the surface defects with different sizes on the life of turbine disk. Its main engineering significance was that based on the stress characteristics of the dangerous position of turbine disk, the fatigue life with existence of the defect can be acquired. And even if the defects are not detected, it can ensure the safety in service period.
Relationship between rotor/vanes blade number andnodal diameter number of bladed-disk coupling vibration
2019, 34(1): 99-105. doi: 10.13224/j.cnki.jasp.2019.01.012
Abstract PDF(883KB) icon1466 icon878
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Targeting the resonant analysis of aero-engine bladed-disk structure, by studying the mathematical formula of the gas excitation and nodal diameter vibration in the revolving coordinate and based on the positive work condition when the gas excitation acted on the bladed-disk structure, a relational expression dm=kNv-nNb describing the relationship between the number of nodal diameter and rotor/stator was deduced while the structure was in resonance. Three numerical examples were given to illustrate the above relation: from the perspective of aerodynamic work and harmonic response, a bladed-disk structure was in resonance while the above relation existed and the excited frequency was equal to structural natural frequency, and moreover, partial blades may be in serious vibration state while the above-mentioned frequency was equal even if the fore-mentioned relation was not satisfied.
Investigation and design for TMF test method of elastic sheet
2019, 34(1): 106-114. doi: 10.13224/j.cnki.jasp.2019.01.013
Abstract PDF(1002KB) icon759 icon568
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Targeting the requirements of thermal mechanical fatigue (TMF) test for elastic sheet, the method of loading pressure and thermal loads was put forward using mechanical design technology, mechanical and electrical technology, cooling technology and data acquisition technology, a parallel test control system of two parallel loads, five test pieces was set up, and a thermal mechanical low cycle fatigue exerciser for elastic sheet was designed. Test results showed that, the system can simulate both the pressure load and thermal load of the elastic sheet in the service environment. The thermal mechanical low cycle fatigue test of elastic sheet was carried out by this test system, and the failure modes of elastic sheet in service state were found. The test system had good repeatability, high loading frequency and loading accuracy. The maximum relative error of pressure load was 2.4%, and the absolute error was less than 0.5N. The maximum relative error of temperature load was 3.55%, and the maximum absolute error was 3.89℃.
Analysis of effect factors on damping characteristics for underplatform dampers
2019, 34(1): 115-124. doi: 10.13224/j.cnki.jasp.2019.01.014
Abstract PDF(975KB) icon723 icon549
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Damping performance of the underplatform damper was numerically investigated on the basis of a simplified model of blades with an underplatform damper. The harmonic balance method was employed to predict the blade response in the frequency domain. A simple expression of the Jacobian matrix by means of discrete Fourier transform was proposed, allowing acceleration of the harmonic balance method. Result showed that, the computational efficiency was improved more than 8 times in terms of blade response prediction. The impacts of key parameters, including centrifugal force, damper mass, excitation level, underplatform angle and the rolling motion of the damper, were thoroughly investigated.
Interaction between surface and interface cracks in thermal barrier coatings under thermal load
2019, 34(1): 125-124. doi: 10.13224/j.cnki.jasp.2019.01.015
Abstract PDF(1282KB) icon948 icon578
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In view of the problem of crack failure of thermal barrier coatings(TBCs) prepared by means of APS, based on the thermal elastic and elastoplastic constitutive relations of the coating system, and taking into consideration the concave and convex morphology of ceramic coat (TC)/oxide layer(TGO)/bond coat(BC) interface, the crack evolution model was established by fracture mechanics and damage mechanics theory respectively according to the difference of position and nature of surface and interface cracks. In combination with contour integral and cohesive element method, the fracture parameters and cracking state of the surface and interface cracks under the thermal load were analyzed, the interaction between the surface cracks of the thermal barrier coating and the interface cracks of the BC/TGO was studied, and the crack failure mechanism under the coupling of thermal, force and chemical fields was revealed. The results showed that the surface cracks greatly changed the stress distribution state in the interface microregion. When the surface crack was near the interface, the interface crack propagation increased by 20%, and the nonuniformity of the crack in the adjacent convex peak can reach 81%. The fracture parameters of the surface crack were mainly dominated by the thermal mismatch and the defects of the multilayer structure. The effect of interface crack on the surface crack was relatively small. The results of the analysis were in agreement with the test results.
Statistical characteristics of forced response in mistuned bladed disks based on high-fidelity finite element model
2019, 34(1): 135-141. doi: 10.13224/j.cnki.jasp.2019.01.016
Abstract PDF(773KB) icon655 icon553
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The extreme value theory was used to analyze the statistical characteristics of maximum forced response of the mistuned bladed disks, and applied to a compressor disk. The mistuning bladed disk was reduced and modeled. The Monte Carlo method was used to simulate the response calculation, and the distribution characteristics for the amplification factor of the maximum response under different engine order excitations were studied. The extreme value theory was used to model the maximum response distribution, and the maximum likelihood estimation method was introduced to get the unknown parameters. The K-S(Kolmogorov-Smirnov) test was employed to test the goodness of fit of different distribution functions. The statistical characteristics of the response of a compressor disk were analyzed. The fitting results of seven kinds of distribution functions for the amplification factor of the maximum response were compared. Results showed that the fitting effects of the extreme value distribution, two-parameter Weibull distribution, normal distribution, lognormal distribution and Gamma distribution were all poor; the fitting effect of the commonly used three-parameter Weibull distribution was not as good as that of the generalized extreme value distribution. Therefore, the generalized extreme value distribution can more accurately describe the statistical characteristics of the dynamic response of mistuned bladed disks.
A method for controlled circulation trailing edge design ofcompressor blade
2019, 34(1): 142-155. doi: 10.13224/j.cnki.jasp.2019.01.017
Abstract PDF(2014KB) icon790 icon551
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A controlled circulation trailing edge design method for compressor blade was proposed to increase the circulation and the turning angle of cascades through the specific geometrical modelling at the region of 2% chord length of trailing edge. The conclusion was verified under different Mach numbers and Reynolds numbers. The numerical results showed that, for the cascade with the diffusion factor up to 0.52 at design condition, the controlled circulation trailing edge can improve the flow turning angle by about 21% while the total pressure loss was nearly kept unchanged. Some controlled circulation trailing edge designs can even have positive effect on the decrease of loss. At the same flow turning angle, the cascade with the controlled circulation trailing edge can have lower total pressure loss than that with traditional rounded trailing edge.
Application of compressed sensing in circumferential modal identification of axial compressor
2019, 34(1): 156-167. doi: 10.13224/j.cnki.jasp.2019.01.018
Abstract PDF(1471KB) icon851 icon572
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Application of compressed sensing in the recognition of azimuthal modes in axial compressor ducts was studied. Compressed sensing of sparse mode signals with various sampling numbers and distributions was performed by means of numerical experiments. For determined signals with different sparsities, effects of the undersampling factor and the sensing constant on the probability of successful reconstruction were discussed. The probability of success was more than 90% when the sensing constant was larger than 3.5. For blind signals, no specific pattern of signal reconstruction was observed. On this basis, a dual-uniform distribution of sampling points was proposed, by combining the advantages of Nyquist-Shannon sampling theorem and compressed sensing. It indicates that the feasibility of sensing depends on the wave number differences and the number of measurement points. When appropriate number of sampling points was selected, the reconstruction of azimuthal modes was reliable. The robustness of this dual-uniform distribution was also investigated. It was verified that a signal composed of 5 modes can still be reconstructed with 3 of the sensors break down. Eventually, compressed sensing was successfully applied in the recognition of azimuthal modes arising from rotor-stator interference based on the Tyler-Sofrin theory. An innovative technique discussed gives a good option in measuring and analyzing azimuthal duct modes of axial compressors.
Optimal sampling strategy for aero-engine blade inspection with coordinate measuring machine
2019, 34(1): 168-176. doi: 10.13224/j.cnki.jasp.2019.01.019
Abstract PDF(797KB) icon735 icon536
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In view of the inefficiency of inspecting aero-engine blades with coordinates measuring machine, unified mathematical descriptions of common sampling algorithms were proposed based on lever system, meanwhile, an optimal sampling algorithm for airfoil surfaces inspection with coordinate measuring machine was presented. By introducing torsion information, the curvature-arc sampling algorithm was appropriate to space curves, and based on this, the algorithm for sampling cross sections on the blade surface through the leading and the trailing edge curves was proposed. And the optimization method of weights in curvature-arc sampling was researched also. Finally, several experiments for different blades were implemented, and the comparisons of optimal sampling points reconstruction errors with those of equal-parameter sampling, equal-arc sampling, curvature-based sampling, equal-deviation sampling and weighted curvature-based sampling were made. The results indicate that the accuracy of optimal sampling is 11.2% higher at least. And the number of optimal sampling points is 92.3% less than equal-step sampling which is used widely in practice.
Application of variable inlet guide vane with adjustable front and back vane parts in highly loaded fan
2019, 34(1): 177-188. doi: 10.13224/j.cnki.jasp.2019.01.020
Abstract PDF(1444KB) icon747 icon485
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A highly loaded fan with the insufficiency of the stall margin in the states of off-design speed was studied. After numerical simulation of three dimensional flow using commercially available CFD code NUMECA, the change of aerodynamic performance of a variable inlet guide vane (VIGV), and the improvement method of low-speed performance of the fan were investigated, when the VIGVs front and back vane parts can be rotated in large range of angle. Results of numerical simulation indicated that the camber angel of the VIGV was one of the most important influential factors to the performance of the VIGV. The front vane part of the VIGV was rotated at some angle, the actual camber angle of the vane was reduced, helping to delay flow separation on the vanes suction surface, and broaden the VIGVs adjustable angle with a low-loss level. Besides, the VIGV was not sensitive to the position of a slot between the two vane parts, if both of the vane parts were rotated with proper angles. The VIGV improved the adiabatic efficiency of the highly loaded fan under the off-designed conditions, the adiabatic efficiencies were improved by 2.04%, 5.48%, 6.18% and 6.82% at 90% speed, 80% speed, 70% speed and 60% speed. Because the throat line of the fan was further away from the throttle line, the fans surge margin was expanded obviously at off-speed.
Experiment on noise control of trailing edge serrations with sloping root
2019, 34(1): 189-194. doi: 10.13224/j.cnki.jasp.2019.01.021
Abstract PDF(678KB) icon614 icon512
Abstract:
A novel serration with sloping root was designed based on the traditional serrated trailing edge with blunt root on NACA0018 airfoil. The influence of sloping angle on trailing edge noise was studied by an experiment. It was found that the novel serrations can reduce the noise by 3.2-17.1dB at high angle of attack (12°-18°), and had a certain inhibitory effect on the hump shaped noise peak which appeared in the middle sound pressure spectrum at low angle of attack. When the sloping angle was 30°, the hump shaped noise peak was eliminated and the overall sound pressure level had a reduction of 0.2-1.5dB.
Selection of measurement parameters based on eigenvalues and eigenvectors
2019, 34(1): 195-200. doi: 10.13224/j.cnki.jasp.2019.01.022
Abstract PDF(575KB) icon686 icon512
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The problem of how to choose the parameters in the aero engine gas path fault diagnosis was studied. Using engine fault diagnosis matrix, a simple and fast algorithm based on eigenvalues and eigenvectors to compare the advantages and disadvantages between different measurement systems was proposed. The algorithm can directly show the change of the global solution space and the direction of vectors from a geometric perspective. A comparison case study of a single-axis turbojet engine test system showed that the maximum-minimum eigenvalue ratio of the ground test system was 33, and the maximum-minimum eigenvalue ratio of the airborne system was 1008. The ground test system is more advantageous to the fault diagnosis of the single-axis turbojet engine than the airborne system.The algorithm can be used to optimize the layout of sensors in airborne engines, measure sensor layout in bench measurement system, and guide the selection of measurement parameters in engineering.
Monte Carlo simulation for the flow-field structure and aerodynamic heating due to cavities on hypersonic vehicle surfaces in the rarefied flow regime
2019, 34(1): 201-209. doi: 10.13224/j.cnki.jasp.2019.01.023
Abstract PDF(1118KB) icon930 icon591
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In order to solve the problem of local aerodynamic heating due to cavities or imperfections on the hypersonic vehicle surfaces, the direct simulation Monte Carlo (DSMC) was employed to investigate a rarefied and hypersonic flow over cavities at the altitudes of 70, 75, 80km and 90km, while considering the effects of rarefied gas and three-dimensional property on flow-field structure inside the cavity and heat flux over the cavity surfaces. It showed that one primary recirculation region was formed as a result of flow separation and reattachment at aforementioned altitudes. In addition, rarefied gas effect played an important role in flow-field structure and heat flux; as the flight altitude increased, the primary vortex became slender, with its core moving up and top-right-corner part sharpening; and the heat flux consequently concentrated to the top region of the downstream surface of the cavity. Moreover, the inclusion of the third-dimension would preclude main-stream gas molecules from penetrating into the cavity, causing the rise of the core of the primary vortex, and an assumption of two dimensionalities resulted in an overprediction of heat transfer to the cavity surfaces.
Large eddy simulation of supersonic jet mixing flow
2019, 34(1): 210-216. doi: 10.13224/j.cnki.jasp.2019.01.024
Abstract PDF(832KB) icon669 icon613
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On the background of cooling jet flow on the optical window, the supersonic jet flow over a backward facing step was investigated via large-eddy simulation (LES). Based on the implicit sub-grid model, the numerical method utilized the seventh order WENO scheme for spatial discretion, which was validated by the simulation of the supersonic mixing layer. The computational model for supersonic jet mixing flow was identical to the wind tunnel experiment, and the Mach number of the free flow and jet flow were set as 3.4 and 2.5, respectively. The numerical simulation captured the complex flow structures of compressive and expansive waves, as well as the shearing mixing layer and boundary layers. The process of flow becoming unsteady and transiting to turbulence was predicted subtly. The position and shape of large-scale turbulent structures obtained from numerical simulation agreed with experimental images. By the analysis of instantaneous, averaged, and fluctuant flow field, the temporal and spatial evolution of flow structures were revealed, and the feature of density fluctuation was acquainted.
Aero-engine cycle design approach for multiple operating conditions performance reliability
2019, 34(1): 217-227. doi: 10.13224/j.cnki.jasp.2019.01.025
Abstract PDF(1092KB) icon883 icon562
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In order to evolve aeroengine overall performance design from the deterministic design to the probabilistic design, an aeroengine cycle optimization design approach for multiple operating conditions performance reliability based on distributed cooperative response surface method (DCRSM) was proposed. The turbofan engine simulation model with uncertainty component performance was established as an example. The distributed response surface models of thrust and special fuel consumption performance under several typical operating conditions were established by the experimental design and the off design point performance simulation, and then the cooperative response surface model was established for cycle optimization. The non inferiority solution set of the cycle parameters was generated from optimization and verified by the random trial. The results showed that the all cycle parameters from the non inferiority solution set could make the engine overall performance achieve a high reliability of not less than 97.5% simultaneously under all expected operating conditions. From the non inferiority solution set obtained by multiple operating conditions performance reliability cycle optimization method, the most suitable cycle selection can be decided according to the physical truth in engine preliminary design phase.
Research on the inlet flow field and ground vortex under crosswind condition
2019, 34(1): 228-237. doi: 10.13224/j.cnki.jasp.2019.01.026
Abstract PDF(1261KB) icon722 icon532
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The aerodynamic performance of a scaled model of high bypass ratio engine inlet under the ground crosswind condition was studied by combining the numerical simulation and experiments, considering the influence of crosswind and ground suction vortex on the inlet flow field and the effect of crosswind on the ground vortex strength; then the double function of the crosswind on the inlet flow field was explained and analyzed. The results indicated that: according to the generation feature of ground vortex and the influence level of crosswind and ground vortex acted on inlet flow field separately, the process from steady state of ground vortex to being blown off can be divided into three stages, i.e.: the initial stage, the rapid stage and the end stage. With the increase of engine inhalation velocity，the initial blow-off speed and the complete blow-off speed increased, but the corresponding velocity ratio basically kept unchanged; before the ground vortex was blown away completely, the crosswind maked double influence on the inlet flow field by affecting the suction vortex, in the initial stage and the end stage, the influence of crosswind played a leading role in the inlet flow field, similar to no-ground condition, the inlet distortion increased with crosswind in this two stages, in the rapid stage, the influence of ground suction vortex played a leading role in the inlet flow field, the inlet distortion decreased with crosswind.
Tooth surface relief method of spiral bevel gear based on high-order cutting motion
2019, 34(1): 238-247. doi: 10.13224/j.cnki.jasp.2019.01.027
Abstract PDF(1070KB) icon608 icon478
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A method of approximate tooth surface relief in use of standard cutting tool was proposed with the advantage of machine flexibility. The tooth surface equation was established according to different types of modified cutting tool, the relived tooth surface was solved and the meshing FEA model was established. According to the gear meshing simulation of the FEA method, the transmission performances of different relived tooth surfaces were compared, and the arc-edged cutting tool was chosen as the optimization target according to the result. The higher order cutting motion was introduced, and the optimization model of tooth surface approaching was established according to the optimization target. The transmission performances of optimal tooth surface and unrelieved tooth surface were compared. Results showed that the first-order vibration amplitude decreased approximately 16.6% when optimal tooth surface was meshed, and the gear transmission performance was effectively improved.

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