2019 Vol. 34, No. 4

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Numerical calculation and experiment on temperature field offriction heat generation of brush seal
2019, 34(4): 737-743. doi: 10.13224/j.cnki.jasp.2019.04.001
Abstract PDF(996KB) icon1498 icon1330
Abstract:
A numerical calculation model with CFD porous media with friction heat as heat source was built. The temperature field of friction heat generation of brush seal used in a specific aero engine was analyzed. An experimental study of friction heat generation in brush seal with simulating operating conditions was conducted. A kind of technology using infrared camera was developed to get the real-time dynamic temperature field of brush seal. Experimental data was used to analyze and improve the numerical calculation model of heat generation. Based on these results, a stiffness correction factor was introduced and validated. During this study, a kind of calculation and experimental method validated by the experimental data was summarized, and could be used to analyze the temperature field of heat generation of brush seal in aero engine. Result showed that, by utilizing such methods, the error between calculation result and experimental data from simulated real operating conditions reduced from 48.15% to 10.67%.
Planetary gearbox fault diagnosis based on ACMPE, ISSL-Isomap and GWO-SVM
2019, 34(4): 744-755. doi: 10.13224/j.cnki.jasp.2019.04.002
Abstract PDF(1516KB) icon1287 icon1087
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In view of the difficulty of extracting nonlinear and non-stationary vibration signals from planetary gearboxes, a planetary gearbox fault diagnosis method based on adaptive composite multi-scale permutation entropy (ACMPE), improved supervised self-organizing incremental neural network landmark isometric mapping (ISSL-Isomap) and grey wolf optimizer support vector machine (GWO-SVM) was proposed. Fault features of vibration signals were extracted from the complex domain by using ACMPE, and the high-dimensional fault feature set was constructed. ISSL-Isomap was used to reduce the dimension of the high-dimensional fault feature set, and the low-dimensional and sensitive fault features were extracted. The low-dimensional fault features were input into a GWO-SVM classifier to recognize fault types. The analysis results of planetary gearbox fault diagnosis show that compared with the feature extraction methods of multi-scale permutation entropy (MPE) and composite MPE (CMPE), ACMPE has more advantages in classification effect and recognition accuracy. ISSL-Isomap has the best dimensionality reduction effect compared with the dimensionality reduction algorithms of local tangent space alignment (LTSA), isometric mapping (Isomap), weighted Isomap (W-Isomap), supervised Isomap (S-Isomap) and supervised self-organizing incremental neural network landmark Isomap (SSL-Isomap). The fault recognition rate of the proposed method reaches 100% with a certain superiority.
Fault diagnosis of aero-engine inter-shaft bearing based on Deep-GBM
2019, 34(4): 756-763. doi: 10.13224/j.cnki.jasp.2019.04.003
Abstract PDF(975KB) icon1621 icon1054
Abstract:
In view of the difficulty in identifying the fault signal of the inter-shaft bearing of the aero-engine, a deep gradient boasting model (Deep-GBM) was proposed to improve the precision score by learning the feature of vibration signal step by step. Fault simulation experiment was conducted on a type of aeroengine intershaft bearing. Vibration fault signal was decomposed through empirical mode decomposition (EMD) method, and intrinsin mode function (IMF) component sample entropy of nonlinear dynamics parameters was collected as base features. With the model proposed, the aero-engine inter-shaft bearing was diagnosed respectively with fault in inner ring, comprehensive fault in inner ring and rolling element, and in normal condition, with stick-spalled fault and stick-scratched fault. The experimental results showed that the fault diagnosis accuracy of the Deep-GBM reached 87%, 28% higher than that of the traditional machine learning model. Besides, the model has been proved to have good generalization ability.
General Shannon entropy spectrum of swash-platebearing based on MED and LMD
2019, 34(4): 764-771. doi: 10.13224/j.cnki.jasp.2019.04.004
Abstract PDF(930KB) icon1065 icon1044
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To overcome the difficulty of swash-plate bearing early fault features of the helicopter easily immerged in strong background noise, a method based on the minimum entropy deconvolution was proposed through the optimization design of the inverse filter, its kurtosis value was increased by about 3.8 times, the vibration signal was denoised and the weak fault characteristics of vibration signal were enhanced. By using local mean decomposition (LMD) and kurtosis-correlation coefficient criterion to settle the issue of non-stationary and nonlinear signal frequency components of complex demodulation, it can adaptively decompose and optimally reconstruct the non-stationary and nonlinear signal, and improve the signal-to-noise ratio of vibration signal. To settle the issue of coupling modulation and sideband highlighting, through noise reduction in envelope spectrum by introducing the general Shannon entropy, the amplitude ratio of the first-order fault characteristic modulation frequency to the fault characteristic frequency was reduced by about 24%-43%. The diagnosis research results of laboratory signal and the fault diagnosis test system for a type of helicopter swash plate bearing verify that the method is reliable and applicable.
Fault diagnosis of rolling bearing based on noise-resistant Wigner-Vile analysis
2019, 34(4): 772-777. doi: 10.13224/j.cnki.jasp.2019.04.005
Abstract PDF(576KB) icon1178 icon971
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To solve the problem that the time-frequency analysis method Wigner-Vile spectrum (WVS) could not extract the fault feature effectively when the impulsion characteristic fault signal of rolling element bearing is buried by strong background noise, the cyclic spectral density Wigner-Vile spectrum (CSDWVS) time-frequency method was proposed based on the property of cyclostationarity of the bearing’ fault signal by combing the cyclic spectral density (CSD) based on second order cyclostationarity statistics with the WVS. Through the verification of simulation and test, the proposed method had the much more noise-resistant advantages than traditional WV method, and it could extract the inner race fault characteristic frequency of 51.9 Hz and the outer race fault characteristic frequency of 32.1 Hz correctly.
Dynamic modeling for double-impulse behavior of ball bearing in the presence of a spall on inner race
2019, 34(4): 778-786. doi: 10.13224/j.cnki.jasp.2019.04.006
Abstract PDF(889KB) icon1360 icon1180
Abstract:
A ball bearing in the presence of a spall on the inner race was studied. Based on Hertzian elastic contact theory, a research on non-linear excitation mechanism excited by the spall fault was carried out, and the internal excitation mechanism of double-impulse phenomenon was studied. As a result, a novel coupled non-linear dynamic model for double-impulse behavior of the ball bearing with a spall on the inner race was proposed, by considering the contact characteristics between the rolling elements and the bearing races and the excitation mechanism of time-varying displacement and contact force. The coupled solution to the second order non-linear differential equations was obtained by applying the Runge-Kutta numerical integral method, the relationship of double-impulse time spacings extracted from the simulated vibration signal was investigated. By comparison of the simulated, experimental and theoretical double-impulse time spacings under diverse shaft rotating speeds and inner race spall sizes of the ball bearing, all the relative errors between the simulated and theoretical double-impulse time spacings were less than 2 percent, and that between the simulated and the experimental double-impulse time spacings were less than 12 percent. In addition, the simulated signal agreed well with the experimental signal. Consequently, it was concluded that the effectiveness of the proposed nonlinear dynamic model in predicting the double-impulse time separation and vibration characteristics of the ball bearing was well validated.
A calculation method for solution of discharge coefficients in aerostatic bearing
2019, 34(4): 787-795. doi: 10.13224/j.cnki.jasp.2019.04.007
Abstract PDF(946KB) icon1198 icon961
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A calculation method combining the method of separation of variables (MSV) for laminar boundary-layer equations and the analytical solution of Reynolds equation was proposed to study the discharge coefficients of aerostatic bearings. The discharge coefficients were obtained by comparing the mass flow rate obtained by the laminar boundary-layer equations and by Reynolds equation. The bearing capacity from solution of Reynolds equation with the discharge coefficient at the constant 0.8 and laminar boundary-layer equations solved by MSV was studied comparatively. Results showed that the maximum precision of the bearing capacity obtained by the Reynolds equation with the discharge coefficient in this calculation was increased 8% than the bearing capacity from the Reynolds equation with discharge coefficient of 0.8, comparing with the results calculated by MSV. It means that the discharge coefficient is suitable and valid for solution of Reynolds equation.
Geometrical design of tooth surface and characteristics of radial tooth width for face gear with arc tooth
2019, 34(4): 796-803. doi: 10.13224/j.cnki.jasp.2019.04.008
Abstract PDF(788KB) icon1242 icon996
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In order to meet the design requirements of face gear transmission in the field of aviation, a type of arc tooth face gear was proposed and its radial effective tooth width characteristics were studied. The involute tooth profile cylindrical gear with arc tooth was used as the generating gear, and the mathematical model of the gear surface was established by envelope forming. Combined with the equation of tooth surface, the tooth surface was visualized in MATLAB, and the parameterized modeling of the gear was realized through the numerical calculation function of the MATLAB software and the complex surface modeling function of the CATIA software. The restrictive conditions of the inner undercut and the outer tip to the radial effective tooth width were established, and the radial effective tooth width of the face gear was calculated. The influences of the arc radius of the tooth line and the position parameters of the coordinate system on the inner radius, the outer radius and the radial effective tooth width were analyzed. Results showed that, when the arc radius of the tooth line was increased, then the inner diameter was decreased, the outer diameter and the radial effective tooth width were increased. When the position parameter of coordinate system was increased, the inner diameter and the outer diameter were increased and the radial effective tooth width was decreased.
Aerodynamic calculation method of engine stabilityunder actual inlet condition
2019, 34(4): 804-812. doi: 10.13224/j.cnki.jasp.2019.04.009
Abstract PDF(967KB) icon1309 icon1224
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Based on the theory of parallel compressor, the calculation method of the influence of actual combined distortion on the engine was studied with the temperature and pressure distortion generated by the steam suction as boundary conditions. The unsteady two-dimensional inviscid integral Euler’s equations were used. While the distortion intensity, the high temperature range, and the low pressure range were kept the same, the regularized equivalent conversion of the distortion contour maps was performed. And the temperature and pressure distortion contour maps were coordinated, so that these two could be superimposed on each other. Results showed that when the number of circumferential sub-engines was greater than 2, the number of sub-engines had little effect on the calculation results. The influence of combined distortion on the fan and compressor pressure ratio was the same as the single pressure distortion. Compared with the experimental thrust loss, the equivalent regularization transformation of the distortion map can be used for the calculation of the actual combined distortion.
Test on starting failure for an aero-engine
2019, 34(4): 813-820. doi: 10.13224/j.cnki.jasp.2019.04.010
Abstract PDF(962KB) icon1415 icon1150
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To solve the incompatibility problem of cold and hot starting for an aeroengine, based on the aero-engine test bed, the ground start of aero-engine was analyzed and the reasons were found. The effects of starter power, starter disengagement speed and starting fuel supply logic on starting performance were studied. Some methods were proposed to improve aero-engine start ability and through the test, correctness of the methods was verified.Test results indicated that the starter power increased by 10% and start time reduced by 5%；the starter disengagement speed was increased by 2% and the starting time was shortened by 18%-25%; if some steps were taken to adjust and optimize the starting fuel supply logic, increased the fuel supply before the start, and reduced the amount of fuel supply in the later period, the starting performance of the engine could be effectively improved.
Three-dimensional shock/shock interaction of airbreathing vehicle’s inlet lip
2019, 34(4): 821-828. doi: 10.13224/j.cnki.jasp.2019.04.011
Abstract PDF(995KB) icon1227 icon1196
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Numerical simulation on three-dimensional interaction between curved oblique shock wave and bow shock wave was studied under the condition of small radius of the cylinder. The numerical method validation was carried out by using the typical three-dimensional aerodynamic interference model. The entrance boundary condition of inlet was obtained by the application of patched grid technology and inverse-distance interpolation method. It indicated that three-dimensional feature of the interactions was strong as the curved oblique shock and bow shock intersected at small angle and six types of shock-shock interactions proposed by Edney may exist over the lip along the lateral direction, although the radius of cowl lip was small. Thermal environment induced by the type Ⅲ and type Ⅳ shock-shock interactions was severe. And the shape of the high heat flux region was like a “scar” on the cowl lip. Heat flux of the scar was 4 to 6 times of the reference heat flux under the same flow condition. This may lead to the ablation or structure damage of the cowl lip.
Numerical simulation of contra-rotating propeller flowfield aerodynamic interactions
2019, 34(4): 829-837. doi: 10.13224/j.cnki.jasp.2019.04.012
Abstract PDF(1149KB) icon1578 icon1119
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On the basis of dynamic patched grid technology, numerical simulations were implemented on an isolated single-rotating propeller (SRP) configuration by means of solving three-dimensional unsteady Reynolds averaged Navier-Stokes (RANS) equations, and the numerical results were verified by wind tunnel test, showing good agreements with the experimental data. Subsequently, emphasis was placed on investigation of the unsteady flowfield characteristics and aerodynamic interactions of contra-rotating propellers (CRP) configuration. The results showed that the unsteady RANS approach allow for a detailed analysis of the developing characters of the slipstream flowfield and aerodynamic interactions between the two propellers. The main reason of the aerodynamic interactions lied in the mutual effects of the blade tip vortices generated by the front and aft propellers, and the aft propeller reduced the strength of the blade tip vortices of the front propeller. Aerodynamic interactions could lead to the periodic oscillations of the aerodynamic forces, and the frequency of the oscillations was linked to the blade numbers. The 6×6 CRP configuration had 12 aerodynamic oscillations in one full rotation. The freestream could be accelerated twice when passing through the CRP, therefore compared with SRP, the thrust coefficient and power coefficient of CRP almost would be doubled in the same working conditions, meanwhile the efficiency would increase by approximately 1.5%.
Regularization method for subsonic hovering rotor sound source reconstruction
2019, 34(4): 838-846. doi: 10.13224/j.cnki.jasp.2019.04.013
Abstract PDF(980KB) icon881 icon545
Abstract:
The aeroacoustic inverse problem was solved according to the aeroacoustic noises radiated by the rotor. The blade surface loading was given and acoustic analogy method was used to obtain the observation data. A large set of ill-posed equations were solved by singular value decomposition combined with the regularization method. In order to overcome the obvious numerical oscillations, a polynomial function was used to represent the unknown, at the same time the Kutta condition was introduced as a priori information. The results showed that under ideal condition, the pressure of the rotor surface obtained by this method was closer to the input value, especially in the tip region. Under certain interference noise, the maximum relative error of the pressure peak position obtained by this method was reduced from 15% to 4%.
HCF/LCF complex fatigue analysis of propeller shaft based on the worst-case equilife curve
2019, 34(4): 847-851. doi: 10.13224/j.cnki.jasp.2019.04.014
Abstract PDF(717KB) icon988 icon607
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Based on Goodman curve, the worst-case equilife curve considering the influence of the stress concentration and the dispersion coefficient of fatigue strength was constructed firstly, and then the worst-case equilife curve was used to establish the high-cycle fatigue/low-cycle fatigue (HCF/LCF) complex fatigue analysis method of the propeller shaft, and this method was used to predict the safety life of propeller shaft, but the applicable range of the prediction method the low-cycle fatigue was between 103 and 105 cycles. Adopting this method, the HCF/LCF complex fatigue of an aero-engine propeller shaft under two kinds of loads was analyzed, and compared with the experiment. The result shows that it is feasible to predict the HCF/LCF complex fatigue of the propeller shaft using the method based on the worst-case equilifecurve; and it can successfully predict a kind of loads safety life lower than 1000 cycles of low-cycle fatigue, and another kind of loads prediction result fits well with the experimental one.
Strength prediction of 3-D four directional C/C composites by high temperature and oxidation environment
2019, 34(4): 852-863. doi: 10.13224/j.cnki.jasp.2019.04.015
Abstract PDF(1100KB) icon894 icon538
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Based on progressive damage method, a kind of high temperature strength prediction model of 3-D four directional C/C composites was established on microscopic scale. The section shape of fiber bundle after extrusion, periodicity of unit cell, and fiber bundles debonding were taken into account in the model. The 3-D Hashin failure criterion considering temperature was introduced to determine the elements failure. And then the tensile strength prediction of 3-D four directional C/C composites at room temperature and 700 ℃ under oxidation protection was achieved. In order to introduce the model in high temperature oxidation environment, the mechanical property degradation model of fiber bundles was established in consideration of oxidation rate. The mechanical properties equivalence of fiber bundles and unidirectional plates was proposed. The tensile strength of 3-D four directional C/C composites without oxidation protection was predicted. Trimming process influence on the strength of 3-D four directional composites was investigated, and the strength prediction model of trimming 3-D four directional composites considering trimming width was established. The tensile strength of trimming 3-D four directional C/C composites with and without oxidation protection 18 mm width was predicted. Results show that the prediction errors are 5.51%, 7.20% and 7.13% for non-trimming specimens at room temperature, 700 ℃ with anti-oxidation coating and 700 ℃ without anti-oxidation coating. The stress-strain curve of tensile process for prediction is quite in accord with experiment. The prediction errors are 0.88% and 4.53% for trimming specimens at room temperature, 700 ℃ with anti-oxidation coating. Several kinds of examples show that the prediction model is reasonable and reliable.
Influence of thermoplastic tackifier on dry fiber placement-RTM process and mechanical properties
2019, 34(4): 864-874. doi: 10.13224/j.cnki.jasp.2019.04.016
Abstract PDF(1190KB) icon956 icon560
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In order to study the effect of thermoplastic tackifier addition on the dry fiber placement-RTM(resin transfer molding) process, T-peel test was utilized to determine the mass fraction of PA-6 tackifier. Combining the test with process simulation, the effect of tackifier on the in-plane permeability of preform with PA-6 as the tackifier was studied. The mold filling process was stimulated and analyzed. On this basis, the influence of tackifier on the interlaminar properties and toughness of epoxy composites was studied. The test and simulated results of permeability of preform with tackifier showed that the permeability of fiber preform in parallel with and perpendicular to fiber direction reduced by 55.5% and 52.0%, respectively. The test results were consistent with the revised simulated results, and the deviation values of filling time with different penetration distances were all smaller than 10%. The results of mechanical test showed that the toughness of epoxy composites could be enhanced significantly by adding thermoplastic tackifier. The mode Ⅰ and Ⅱ interlaminar fracture toughness improved by 89.3% and 54.1%, respectively. While the impact toughness improved by 18.7%, the interlaminar shear strength reduced by 23.6%.
Influence of CMAS on residual stresses of EB-PVDthermal barrier coating system
2019, 34(4): 875-884. doi: 10.13224/j.cnki.jasp.2019.04.017
Abstract PDF(1165KB) icon946 icon581
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A finite element model of electron beam-physical vapor deposition (EB-PVD) thermal barrier coating (TBC) considering crystalline columns was developed, the influence of CMAS deposition and penetration on residual stresses was systematically studied. The results showed that large in-plane and out-of-plane residual tensile stresses were induced by CMAS deposition and penetration, the vertical and horizontal cracks were easily initiated and propagated, finally TBC failed due to the spall off and delamination. These failure modes mainly happened at three regions: closely beneath the surface of TC, the interface between CMAS penetration and none penetration zone, and close to the top coating/bond coating(TC/BC) interface.
Compression performance of open-hole composite laminates reinforced by Z-pin
2019, 34(4): 885-893. doi: 10.13224/j.cnki.jasp.2019.04.018
Abstract PDF(1082KB) icon961 icon567
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Z-pin reinforced technique was used to improve the performance of open-hole composite laminates, in view of load capacity reduction because of the stress concentration at the edge of the hole. The influence of the Z-pin insertion percentage on the compression performance of open-hole composite laminates was analyzed by testing the compression properties of laminates with different Z-pin inserted percentages, finite element models of the classical cohesive elements and open-hole composite laminates were established to analyze the influencing mechanism. Results showed that the reinforcing pins increased the compressive strength by 23.06% maximally. Only along the compressive loading direction, the Z-pin located on both sides of the hole can reduce the damage expansion speed by bridging force, but the ultimate failure mode of laminates was not changed. Numerical results showed that the compression damage extended from the edge of the hole to both sides, and the lamination in the center of the laminate was the first to be damaged, among which the cohesive elements in the 6th and 10th layers were the first to be damaged. The simulation results were in good agreement with the test results.
Flame structure and dynamics characters investigation by OH and CH2O planar laser-induced fluorescence in the swirl combustor
2019, 34(4): 894-907. doi: 10.13224/j.cnki.jasp.2019.04.019
Abstract PDF(2062KB) icon1424 icon685
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The swirl combustor model of aircraft engine under fuel-lean condition was characterized by planar laser-induced fluorescence (PLIF) technique. By taking PLIF measurements of OH and CH2O simultaneously, the transient structures of the reaction zone and preheat zone were investigated under various operation points. By applying proper orthogonal decomposition (POD) method to the OH PLIF data, the main dynamics modes of the swirling flame were extracted, and by applying extended proper orthogonal decomposition (EPOD) method, CH2O PLIF signal distribution for each POD mode was unveiled. The experimental results indicate that as the thermal power of the combustor increases, the time-averaged structure and dynamics modes experience notable transitions. As the flame elevated, the flame exhibits stronger axial instability, while the deformation caused by precessing vortex core (PVC) is decreased. At relative high thermal power, unburnt fuel emerges in the external recirculation zone (ERZ).
Research on skin-friction drag and drag reduction technics in a supersonic inner flow path
2019, 34(4): 908-919. doi: 10.13224/j.cnki.jasp.2019.04.020
Abstract PDF(1399KB) icon1010 icon604
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In a constant-cross-confined-space with rearward facing steps, the skin-friction drag and drag reduction technics in a supersonic inner flow path was developed by three-dimensional numerical simulation. The influential mechanism of skin-friction drag in the same mass hydrogen injection and combustion but under different air inlet conditions and combustor entry conditions when the scramjet engine operated from flight Mach number 5, 6, 6.5 and 7, and different injecting pressure effects on the wall shear stress beheading the injectors were analyzed and compared. The results show that the drag reduction effect under low injection speed is more obvious than that under high injection speed. 507 kPa obtains 10% drag reduction and 50.7 kPa obtains 5%. Boundary layer combustion achieves almost 70% drag reduction. When the fluid passes backward facing step, regularly uneven changes of wall shear stress will appear and the biggest difference is 100%. The trends of wall shear stress and density are basically the same. Therefore, the key point of skin-friction drag reduction in inner flow path is building low density field near the wall surface. The area with stable and effective drag reduction effect is located more backwards of the injectors. However, due to the mixing and consumption of fuel, the drag reduction effect gradually decreases along the flow direction.
Study of the temporal and spatial characteristics for swirling flame heat release rate based on CH chemiluminescence
2019, 34(4): 920-928. doi: 10.13224/j.cnki.jasp.2019.04.021
Abstract PDF(1057KB) icon859 icon561
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Several swirling CH4/air diffusion flames were investigated in a gas turbine model combustor via the temporal phenomenon of thermos-acoustic and the spatial flame mode transition. In the combustion mode transition, three-dimensional computed tomography of chemiluminescence (3D-CTC) technique was utilized due to the complexity of swirling combustion flow field. The 3D emissions of CH* were measured and taken as qualitative indicators of the heat release rate under three Reynolds number conditions (from 5 000 to 20 000). This 3D measurement method utilized 8 multi-directional CH* images as inputs combined with tomographic algorithms to compute the 3D distribution of CH* intensities. In order to verify the reconstruction fidelity, the two-dimensional visualization of the reconstructed shape was compared with the time-averaged projection under high-speed photography, and the results showed that the reconstruction error was within 5%. In this study, the transitions of heat release area with Reynolds number were analyzed, and the results showed that the heat release rate changed more obviously along the nozzle radical direction than the axis direction, and the largest heat release area moved forward significantly. The thermo-acoustic study was obtained by high speed CH* images, finding that the oscillating frequency of heat release increased with the increase of the Reynolds number.
Effects of unsteady combustion process on combustion instability of liquid rocket engine
2019, 34(4): 929-936. doi: 10.13224/j.cnki.jasp.2019.04.022
Abstract PDF(832KB) icon1032 icon571
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Based on theoretical model, the effect of unstable combustion heat release induced by unsteady combustion process, the most important source term of exciting on combustion stability and its triggering mechanism were analyzed and discussed. Then one dimensional premixed laminar flame model was separated into stable and unstable forms by the small perturbation analysis way, and the calculating method for heat release term in linear growth rate was built. With the distributions of temperature and heat release in space, the effects of varying initial temperature and specific heat ratio on this term were investigated. It is indicated that the combustion system using energetic propellants with low initial temperature always behaves more stably. For the same kind of propellant, increasing the specific ratio will make stability more sensitive to frequency, which will be more clearly for some frequency range.
Investigation on heat transfer of solid fuel surface and regression rate of solid fuel ramjet effect by swirl flow
2019, 34(4): 937-949. doi: 10.13224/j.cnki.jasp.2019.04.023
Abstract PDF(1557KB) icon1003 icon519
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In order to investigate the heat transfer of solid fuel surface and regression rate of solid fuel ramjet (SFRJ) effect by swirl flow, high-density polyethylene (HDPE) was used as fuel of SFRJ, the experiments were conducted by using connected pipe facility. And a two-dimensional axisymmetric turbu1ent f1ow and combustion program was developed, the heat transfer between fluid and solid domains was considered, and unsteady time method was used to simulate the case of experiment. The results indicated that the heat transfer in recirculation zone and reattachment point was higher than that in redevelopment zone, and the heat transfer of fuel surface had an appreciable effect on regression rate. Due to the function of centrifugal force and tangential velocity provided by swirl flow, this can lead to the long residence of pyrolysis of HDPE, and has positive effect on the combustion efficiency near the fuel surface. Moreover, the swirl flow can also increase the ability of heat transfer of fuel surface, the heat transfer coefficient was 100% higher than that of non-swirl flow. Compared with non-swirl flow, the combustion achieved for stability could be faster with swirl flow. The experimental result indicate that the introduction of swirl flow has a positive effect on improving the regression rate of SFRJ about 26%, but it can also lead to periodic oscillation of the pressure after burning chamber.
Application of biharmonic equation in optimization design of aero centrifugal pump blade profile
2019, 34(4): 950-960. doi: 10.13224/j.cnki.jasp.2019.04.024
Abstract PDF(1461KB) icon1051 icon606
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In order to reduce the amount of computation and improve the efficiency of optimization process, the optimization design of aero centrifugal pump blade profile based on the biharmonic equation agent model and hybrid artificial fish-swarm algorithm was studied. Five-point fourth-order Bezier curves and linear function were used to control the distribution of the circumference angles and the stacking of the blade profile under the Matlab platform. The numerical simulation of the 15 design results was carried out by the joint batch processing of softwares UG and Fluent. Then based on surface interpolation, the calculation of spatial boundary conditions was obtained, and biharmonic partial differential equation on central difference scheme was solved to establish the hypersurface agent model. The objective function of maximum efficiency was used to optimize the design variables based on the artificial fish swarm algorithm. Results showed that the artificial fish-swarm optimization method based on biharmonic equation agent model can ensure the test value and the predicted value were exactly the same. Compared with prototype the wake effect in the optimized impeller was weakened, and the hydraulic efficiency increased by 5.4%.

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