2017 Vol. 32, No. 12

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Burst pressure prediction of filament wound composite shell
2017, 32(12): 2817-2823. doi: 10.13224/j.cnki.jasp.2017.12.001
Abstract PDF(969KB) icon688 icon594
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For the burst failure mechanism of filament winding composite pressure shell, a progressive failure model based on continuum damage model was proposed. Fiber breakage, matrix damage and fiber/matrix deboned were considered in this model. Nonlinear shear damage was taken into account as the intralamina mechanics of filament wound composite was different with composite plate. The model was implemented into ABAQUS/Standard through UMAT subroutine and used to simulate the tension failure of notched wound composite specimens. The burst failure process of wound composite shell was simulated. The result showed that the ultimate failure of the wound composite shell was induced by fiber breakage. Fiber breakage mainly occurred in hoop layers and matrix damage mainly occurred in helical layers.
Shape design and optimization for shank of aeroengine fan blade
2017, 32(12): 2824-2834. doi: 10.13224/j.cnki.jasp.2017.12.002
Abstract PDF(1125KB) icon606 icon665
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The optimization method for designing the shape of the shank of an aeroengine fan blade was explored, and it was used to improve the vibration property of the fan blade without changing the aerodynamic design of the blade. First, the method for designing the shape of shank based on NURBS (nonuniform rational B-spline) bridging curves was established, and the smooth connection between the passage blade and the tenon sides was achieved. Then the parametric design of the shank shape was accomplished by adjusting the positions of the control points of the bridging curves, and 8 design variables which were required to completely define the shape of the shank were extracted on the basis of related assumptions. The maximization of resonance margin of the fan blade was chosen as the objective of shank design; the optimization process of shank shape design was established based on radial basis function network (RBFN) and particle swarm optimization (PSO), and the principle is that an RBFN metamodel is constructed to approximate and predict the implicit objective function whose input and output are design variables of the shank and resonance margin of the fan blade respectively, and that PSO is used to find the best combination of shank design variable which achieves the maximum resonance margin. The above process was used in the design of a high bypass ratio widechord fan blade, and the shank shape was optimized so that the natural frequency of the axial first order bending mode for the fan blade was increased and that the resonance margin for the excitation frequency that was the triple of the rotation speed was increased by about 2%.
Application of θ projection method in analysis of creep deformation of turbine disc
2017, 32(12): 2835-2841. doi: 10.13224/j.cnki.jasp.2017.12.003
Abstract PDF(905KB) icon699 icon596
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The creep deformation of direct aging ZSGH4169 turbine disc was studied. Firstly, a θ projection model with 16 parameters was established to characterize the creep behavior of the ZSGH4169 superalloy at different temperatures and loads. Secondly, the corresponding user subroutine combined with the general finite element program was developed, and the calculation precision was also validated. Thirdly, the model was used to simulate the creep deformation of the turbine disc. The calculated results show that the model can describe three stages of creep behaviors of ZSGH4169 under 650℃ and 700℃. Compared with the conventional models such as Norton rate model, the model had greater modeling capability and higher accuracy, so it could be used particularly in case of the change of the loading and temperature. Furthermore, the longtime creep deformation and stress relaxation of the turbine disc at the center hole and bolt hole were obtained, providing a guidance for the engineering design.
Estimation of velocity for foreign object that impacting rotor blade of aeroengine
2017, 32(12): 2842-2847. doi: 10.13224/j.cnki.jasp.2017.12.004
Abstract PDF(736KB) icon642 icon537
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Taking the inlet port for a reference system, the velocity equation was developed using the momentum theorem to describe the motion of the foreign object from the inlet port to the rotor blade of aeroengine. Correlations between impacting velocity and impacting direction were founded by taking the rotor blade as a reference system. A kind of airplane and its aeroengine were taken as example, the change rule of the motion velocity in inlet channel was studied at aeroengine 100% design speed when airplane took off the ground. It was found that the foreign object motion velocity related not only with the foreign object shape, dimension, location and material, but also with the aeroengine working state and the length of the inlet port. The impacting direction was nonvertical to the blade surface.
Design of key part on turbine disk using multiarcs method and multivariable optimization
2017, 32(12): 2848-2854. doi: 10.13224/j.cnki.jasp.2017.12.005
Abstract PDF(873KB) icon677 icon561
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In order to obtain the structure type of turbine disk satisfying minimum masses and stress standards, the influence of multiarcs transition on stress distribution at key parts was studied. Doublearcs and threearcs structure design schemes were proposed, and geometric theory on arcs transition was derived to support the design modifications and optimization. Based on finite element calculation, the stress varying with structure parameters was obtained. Based on ANSYS Workbench platform and parametric modeling technique, optimization design variables were chosen to get minimum masses with constrained equivalent stress. Result showed that, the maximum equivalent stress on two parts decreased by 662% and 1140%, the mass of turbine disk decreased by 016%. The results provide useful references for multiarcs design and engineering applications of the gas turbine disk.
Performance modeling of turbofan engine in event of shaft failure
2017, 32(12): 2855-2861. doi: 10.13224/j.cnki.jasp.2017.12.006
Abstract PDF(869KB) icon712 icon631
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To deal with the dynamic performance of a twospool turbofan engine with mixed exhaust in the event of highpressure shaft failure, the transient matching constraints of the failure turbofan engine were established and corresponding components models were built by taking volume packing effects and fluid inertia effects into consideration. On this basis, a parametric analysis was then carried out to study the regularity and mechanism of the transient response of the gas path in engine induced by shaft failure during takeoff and cruising stage. Results showed that the high pressure shaft failure of the turbofan engine could lead to several hazardous events, such as compressor surge, turbine overtemperature and overspeed, within no more than 05s. The time sequence of the above events changed as the shaft failure took place on different flight profile stages. Turbine overspeed was more likely to occur before compressor surge during takeoff stage and the turbine could reach its rupture speed within 012s. Special attention should be paid to all of these in the engine passive safety design.
Optimization of inspection interval for civil aero-engine hotsection subassembly system based on semiMarkov model
2017, 32(12): 2862-2771. doi: 10.13224/j.cnki.jasp.2017.12.007
Abstract PDF(907KB) icon659 icon540
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According to the acquisition of inspection and maintenance information of civil aeroengine hotsection subassembly system and typical degradation state judgment by experts, the models of sojourn time estimation of each typical macro degradation state based on expert estimation opinion, inspection information and their fusion data were set up under the assumptions of the system state degradation process obeying a discrete semiMarkov chain. The methods of maximum likelihood estimation and MCMC(Monte Carlo Markov Chain) were applied to estimate the model parameters, the sojourn time and the state transition coefficients in each macro degradation state based on these three kinds of data. Meanwhile, the state transition probability models were built in a certain service cycle for optimal inspection and maintenance cost, and then the optimal inspection intervals in three typical macro degradation states, ie 1750, 350, 70cycles were obtained by simulation. The results showed the optimal inspection intervals were relatively close to the reality situations in the civil aviation operation and production, providing the technical supports in the aspect of customeroriented inspection and maintenance decisionmaking and improving economic benefits for civil aviation transport enterprises.
Test of multiimpact damage and highcycle shear fatigue of stiffened composite panels
2017, 32(12): 2872-2879. doi: 10.13224/j.cnki.jasp.2017.12.008
Abstract PDF(1156KB) icon640 icon551
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To study the effect of multiimpact damage and highcycle shear fatigue on the damage evolution, buckling behavior and failure modes of stiffened composite panels, nine stiffened composite panels were manufactured with similar configurations, and the impact test, highcycle shear fatigue test and residual shear strength test were designed. During the multiimpact and highcycle shear fatigue tests, the damaged zones were detected by the ultrasonic Cscan system. Cscan images indicated that the length and width of damaged zones increased with the increasing number of cycles. Compared with initial undamaged specimen, the average failure load of specimens with multiimpact damage and highcycle shear fatigue declined about 50%. Furthermore, the failure modes of the specimens were also affected by the initial damage caused by impact or fatigue. For the impact and fatigue specimens, the deformation of local buckling skin appeared, and the failure cracks were much near the impact damaged zones.
Design of compound fatigue test system of compressor blade and fatigue life analysis
2017, 32(12): 2880-2887. doi: 10.13224/j.cnki.jasp.2017.12.009
Abstract PDF(1031KB) icon649 icon595
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In order to simulate the typical working condition of aircraft engine, the effects of the high and low cycle compound fatigue on the fatigue performance of a certain level compressor blade were researched.To achieve the purpose, a high and low cycle combined fatigue test system was designed, and the compound fatigue test, vibration test and simulation analysis were conducted. It was concluded that the first order vibration frequency of the blade of 1530Hz was confirmed, and the compound fatigue test can significantly reduce blade life to 58.6% than pure low cycle loading; through analysis of the curves of S-N and P-S-N , the degree of fitting of SN curve can reach to 099. The fracture of the blades and the macroscopic and microscopic characteristics of the fracture showed fatigue source, high cycle loading extended area,low cycle loading extended area and fracture area at the same time. The clear characteristics area of fracture under the compound fatigue effect was found. The rationality and feasibility of this test system were illustrated.
Parametric simulation method for 3-D non-planar crack propagation
2017, 32(12): 2888-2895. doi: 10.13224/j.cnki.jasp.2017.12.010
Abstract PDF(982KB) icon640 icon537
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An automatic 3-D non-planar crack propagation simulation method based on finite element method (FEM) was developed. This method established cracked block by parametric modeling method, inserted initial crack in structure model by inlaying the cracked block, then acquired crack propagation parameters through FEM analysis; then it automatically updated cracked block to simulate the propagation process of crack. Through the simulation of three crack propagation cases, the crack propagation cycles were calculated; compared with the experimental results, the errors were 19.5%, 16.1%, 2.1% respectively. The results show that this method can simulate nonplanar 3-D crack propagation and calculate propagation life with accuracy and applicability.
Thermal analysis for fast start up of noncontinuous rotor considering thermal contact resistance
2017, 32(12): 2896-2902. doi: 10.13224/j.cnki.jasp.2017.12.011
Abstract PDF(1001KB) icon646 icon530
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The thermalstructure coupling analysis for bolted connection was modeled according to the structural features of noncontinuous rotor, taking thermal contact resistance of rough surface into account. The timevarying relationship of temperature distribution and maximum stress during the fast startup of the turbine was investigated. The influence of contact properties, such as roughness and pretightened force, on temperature distribution, tensioning force and maximum stress was analyzed. Results indicated that, the thermal contact resistance had great influence on temperature distribution of contact surface and maximum stress of bolted connection under the thermal impact, the contact property had influence on temperature distribution, deformation distribution and maximum stress. The research provides theoretical basis for the design of gas turbine, contributing to the analysis of thermally induced vibration and fault diagnosis.
Research on stability reliability of pipe conveying fluid based on finite element method
2017, 32(12): 2903-2909. doi: 10.13224/j.cnki.jasp.2017.12.012
Abstract PDF(768KB) icon657 icon558
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For analysis of the stability reliability of spatial aeroengine pipe system, a probabilistic reliability method based on finite element method (FEM) and Monte Carlo method (MCM) was proposed. A fluidstructure coupling model of the pipe system was established with FEM. A limit state function of stability reliability was presented on the basis of analysis of natural frequency. The stability reliability was calculated using MCM. The analysis results of typical pipe system showed that: for a given mean flow velocity, as the variation of flow velocity increased, the divergence instability probability may increase or decrease; for a given variation of flow velocity, the probability density function of limit state function changed to the mixed probability density function from the continuous probability density function as the mean value of flow velocity increased. The result is valuable for stability reliability design and analysis of pipe system conveying fluid.
Effect of radial cooling channel sectional characteristic length on air cooled flameholder
2017, 32(12): 2910-2918. doi: 10.13224/j.cnki.jasp.2017.12.013
Abstract PDF(1072KB) icon571 icon454
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To study the impact of radial cooling channel section characteristic length change on air cooled flameholder cooled flow field, the cooling performance and flow loss, and also provide reference for further optimization design, a numerical simulation was performed by using an experimentally validated CFD method. Within the range of the characteristic length, the results indicated that, increasing the characteristic length reduced the lower portion intake resistance of radial cooling channel, so the air pocket entraining rate caused an increase of 667%. Due to the impact of vortex, the mass flow of the vent holes at the lower portion was significantly lower than that at the upper portion. Changing characteristic length had little effect on the mass flow distribution. Increasing the characteristic length enhanced the outer wall cooling effect of radial flameholder adjacent to the ring flameholder, but weakened the outer wall cooling effect of radial flameholder close to the inner cone. Due to the increase of the characteristic length, outlet total pressure recovery coefficient decreased by 0086% and total pressure recovery coefficient distribution curve along the afterburner moved downward.
Partial load tests on a twostroke spark ignition direct injection heavy fuel engine
2017, 32(12): 2919-2926. doi: 10.13224/j.cnki.jasp.2017.12.014
Abstract PDF(979KB) icon619 icon480
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The partial load tests at the engine speed of 3000r/min and 10%,20% throttle open positions were carried out on a twostroke spark ignition dieselfuelled engine with airassisted direct injection, and the effects of ignition and injection parameters on the engine performance were investigated. The tests results indicated that, at the small throttle open position, applying the strategies of the ignition timing at 30°-40° crank angle before top dead center, the saturated ignition energy, the partial lean mixture (excessairratio above 11) and the suitable injection timing can fully improve the engine power output and fuel economy. With the increase of engine load, the effects of the ignition energy reduced. Applying the strategies of the moderate delayed ignition timing, the partial rich mixture (excessairratio below 10) and advancing the end of injection timing to increase the fuel evaporation time resulted in a remarkable engine power output. Furthermore, the fuel economy and HC/CO emissions of the engine improved greatly by the use of the saturated ignition energy and the partial lean mixture (excessairratio above 1.15).
Numerical simulation of discrete holes supersonic gaseous film cooling
2017, 32(12): 2927-2933. doi: 10.13224/j.cnki.jasp.2017.12.015
Abstract PDF(876KB) icon552 icon459
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In order to get the effect law on the efficiency of gas film entrance structure and provide a reference for engineering application, 3D discrete holes supersonic gaseous film cooling numerical simulations with different holes structure were investigated. Results showed that the film inlet structure affected the film cooling efficiency obviously. Flow coefficient affected the cooling directly so that film cooling effectiveness reduced 005 while flow coefficient decreased 013 for the axisymmetric entrance under calculation conditions. Meanwhile, lowing jet holes area change rate enhanced the cooling effectiveness, because the flow field with too fast area change rate can't develop fully, and the gaseous film flowed to both sides while the center was exposed to combustion gas. Design of a rectifying section in discrete holes exit will help to concentrate the coolant and keep off the cooling deterioration with the layer of film penetrated.
Heat and mass transfer characteristics of alkali metal working medium in porous wick evaporator based on capillary pumped loop
2017, 32(12): 2934-2940. doi: 10.13224/j.cnki.jasp.2017.12.016
Abstract PDF(829KB) icon578 icon448
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Taking porous wick evaporator based on the principle of capillary pumped loop (CPL) as object and considering the wick, vapor groove and casing as a whole, the heat transfer and phase change characteristics of alkali metal working fluid in the porous wick evaporator were analyzed by numerical simulation method. The distributions of vapor phase volume fraction, temperature, pressure and velocity of working medium were obtained. The results showed that the average superheat of porous wick was less than 1K due to high thermal conductivity of alkali metal liquid. The evaporation of alkali metal liquid took place at outside surface of the porous wick and the liquidvapor interface was maintained at wickgroove interface. Under the same parameter conditions, the evaporator using alkali metal had greater transport capacity since its capillary force was 1 to 2 orders of magnitude higher than that of the evaporator using conventional working fluid.
Experiment of laminar combustion characteristics of 1,3,5trimethylbenzene
2017, 32(12): 2941-2946. doi: 10.13224/j.cnki.jasp.2017.12.017
Abstract PDF(839KB) icon526 icon429
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In order to investigate the laminar combustion characteristics of 1,3,5trimethylbenzene and influence factors, the high speed schlieren technology and constant combustion bomb technology were used to carry out some experiments. The Markstein length and laminar burning speed were obtained under different initial conditions; in combination with the mechanism of the reaction of 1,3,5trimethylbenzene, it revealed the key elemental reactions leading to the change of laminar burning speed under different initial conditions, and the fitting formula of laminar burning speed was built at different initial pressures and initial temperatures. The accuracy of the fitting formula was verified, and the laminar burning speed of 1,3,5trimethylbenzene/air mixture under different initial conditions was calculated. The results show that the laminar burning speed of 1,3,5trimethylbenzene/air mixture increases with the increase of initial temperature, and decreases with the increase of initial pressures, while Markstein length decreases with the increase of initial pressure and initial temperature.
Heat transfer characteristics in twopass ribroughened trapezoidal channel at high rotation number with different model orientation angles
2017, 32(12): 2947-2954. doi: 10.13224/j.cnki.jasp.2017.12.018
Abstract PDF(1041KB) icon614 icon492
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In order to study the effects of rotation on a realshaped internal cooling channel in the high pressure turbine blade, the heat transfer characteristics of a twopass trapezoidal channel with vertical ribs were studied experimentally, with Reynolds numbers range of 10000－50000, rotation number range of 0－209 and the model orientation angles of 0°, 225°and 45°. The results indicated that: for the stationary case, the heat transfer at the trailing wall was stronger than that at the leading wall in the first channel, but it was only slightly larger in the second channel. For the rotating case with the model orientation angle of 0° to the axis of rotation, as the rotation number increased, the heat transfer difference between the trailing wall and the leading wall became larger in the first channel, while the heat transfer at the leading wall gradually became stronger than that at the trailing wall in the second channel. At a high rotation number (rotation number was more than 1), the heat transfer was the largest for the case with 0°model orientation angle, and the smallest for the case with 45°model orientation angle.
Experiment on microscale flames stabilized on surface of annular porous media
LIN Peihua, LIN Yuzhen, XUE Xin, ZHANG Liang, ZHANG Chi
2017, 32(12): 2955-2963. doi: 10.13224/j.cnki.jasp.2017.12.019
Abstract PDF(885KB) icon531 icon440
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The characteristics of the surfacestabilized flame on a porous medium in an annular microscale channel were studied experimentally with methane/air mixture. In the pressure drop characteristic study, three porous media with the same pore diameter and different porosities were used and compared. The substitution of the air for the mixture was verified accurately at first. Then the relationship expression of the air pressure drop characteristic was acquired for each porous medium according to the Forcheimer correlation. The third porous medium was selected for the following research, as it had the expression closer to the Darcys law. As for the ignition characteristic study of the surfacestabilized flame, a reasonable criterion was established for the flammability limit determination. Based on the criterion, the result showed that the limit reached the minimum value when the mixture equivalence ratio was 0.9. During the extinction characteristic study, through the welldesigned operating procedure, the experiment was conducted to obtain the strict extinction limit of the surfacestabilized flame. It was indicated that the extinction limit at mixture equivalence ratio of 08 was the least.
Experiment on infrared signature of a model of serpentine twodimensional exhaust system
2017, 32(12): 2964-2971. doi: 10.13224/j.cnki.jasp.2017.12.020
Abstract PDF(1558KB) icon569 icon464
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The pressure and temperature distributions on the surface of a model of serpentine twodimensional（2D）nozzle exhaust system were measured, and its infrared radiation(IR) intensity on the side, lower and upper detection planes were also measured; these results were compared with those of a relevant axisymmetric exhaust system. The results showed that, the radiation intensity of serpentine 2D nozzle exhaust system on the upper detection plane was much higher than that on other two planes, with the maximum value at angle 10°; compared with axisymmetric exhaust system, the radiation intensity of serpentine 2-D nozzle exhaust system reduced by 75.5% at angle 0°, and 57.6%, 50.9% and 17.3% at angle 90° respectively on the side, lower and upper detection planes.
Study on antiknock quality strategies of twostroke kerosene engine
2017, 32(12): 2972-2980. doi: 10.13224/j.cnki.jasp.2017.12.021
Abstract PDF(979KB) icon611 icon517
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An onedimensional performance simulation was made to solve the problem that the knock limited power of a 2stroke aviation engine decreases due to the use of aviation kerosene. Several technical measures were proposed to boost the knock limited power of engine. Under the rated condition that specific fuel consumption and exhaust temperature did not deteriorate, adding antiknock additive, decreasing compression ratio and retarding ignition timing mitigated the knock tendency after using kerosene as the fuel instead of gasoline. Enlarging cylinder diameter and decreasing the Airfuel ratio were beneficial to the recovery of knock limited power of engine. Result showed that，after optimization, the engine regained 96% of original output power. The specific fuel consumption increased by 19% and exhaust temperature increased by 57K. The research results provide the basis for performance optimization and work reliability of twostroke kerosene engine.
Experiment of impingement heat transfer characteristics in dimpled wedge channel
2017, 32(12): 2981-2987. doi: 10.13224/j.cnki.jasp.2017.12.022
Abstract PDF(880KB) icon582 icon427
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In order to obtain the hot air antiicing properties of engine inlet strut, an impingement heat transfer experiment was carried out in a dimpled wedge channel with use of transient thermochromic liquid crystal measurement technique. The effects of jet Reynolds number (Re), distance between jet entrance and dimple, dimple space and the number of dimple rows on Nusselt number (Nu) were studied. The results shows that Nu increases with the increasing Reynolds number, and the heat transfer of dimpled wall is stronger than that of smooth wall. Local Nusselt number reaches a maximum at the trailing edge of the dimple. The average heat transfer effect of side walls increases when the dimple space decreases. When the dimples are close to the outlet, there is an obvious enhancement to the side wall Nu at small Re, while the heat transfer at the leading edge is enhanced at relative large Re. When the number of dimple rows increases, the average Nu increases.
Parallel plans for TBCC variable geometry inlet
2017, 32(12): 2988-2996. doi: 10.13224/j.cnki.jasp.2017.12.023
Abstract PDF(1128KB) icon619 icon507
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With analysis on parallel plan for parallel turbine based combined cycle (TBCC) inlets, a method for classification and a type of parallel plan were proposed. Numerical simulations were conducted for four types of parallel plan inlet during the mode transition at Mach number of 25. Results showed that total mass flow rate kept nearly constant for pure internal parallel plan, contributing to stable thrust during mode transition; total mass flow rate decreased for other three plans. Pure externalparallel inlet with back door had the lowest mass flow rate of ramjet channel with a large change, other three plans had a small change. Total pressure recovery at turbine channel exit increased from a lower initial level during mode transition for pure internal plan; it decreased evidently from a high initial level for external parallel plan, but decreased within a narrow range for mixed internal plan.
Flow structure of underexpanded elliptic jet
2017, 32(12): 2997-3003. doi: 10.13224/j.cnki.jasp.2017.12.024
Abstract PDF(993KB) icon586 icon497
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To reveal the flow characteristics of a supersonic underexpanded elliptic jet, the flow structures of underexpanded elliptic jets at the nozzle pressure ratio N of 14, 24 and 40 were simulated using largeeddy simulation (LES) in combination with the high order hybrid schemes. The threedimensional (3D) flow characteristics and the evolution of underexpanded elliptic jet were illustrated from the results, and the reason for the different shock structures of the minor and major axis planes introduced by nonuniform curvature of the nozzle was discussed. Moreover, the results also found that the Mach shock reflection happened on the minor axis plane at N being 24, but regularreflection remained on the major axis plane. The shock structure of both major and minor axis planes were transferred into Mach reflection when N was 40. Therefore, the nozzle pressure ratio introducing the Mach shock reflection increases as the nozzle curvature radius becomes gentle.
Analysis of aerodynamic interaction andtrim characteristics of rigid coaxial rotor
2017, 32(12): 3004-3012. doi: 10.13224/j.cnki.jasp.2017.12.025
Abstract PDF(971KB) icon566 icon490
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A numerical method based on highefficient trim strategy and moving overset grid technique was developed to predict the aerodynamic characteristics of rigid coaxial rotor. To simulate the rotors flowfield, the Reynoldsaveraged NavierStokes equations were discretized by Roemonotone upstreamcentered schemes for conservation laws(MUSCL) scheme with SpalartAllmaras turbulence model. A delta trim method was implemented. Researches on the aerodynamic interaction and trim characteristics of a coaxial rigid rotor model were conducted. Results indicated that the delta method consumed much less time than the conventional trim method with the same accuracy. The aerodynamic interaction of rigid coaxial rotor, with a smaller rotors distance, was much stronger than that of normal coaxial rotor. In hover condition, the lower rotor required greater collective pitch while providing less tensile force due to the upper rotors downwash; in low speed forward flight, the aerodynamic interaction brought about a more asymmetrical airflow on the rotors disks, leading to greater difference of cyclic pitches. In addition, the rotors power efficiency can be improved by a proper lift offset.
Aerodynamic acoustic field of axisymmetric supersonic jet at low and moderate Reynolds number
2017, 32(12): 3013-3021. doi: 10.13224/j.cnki.jasp.2017.12.026
Abstract PDF(917KB) icon544 icon387
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Acoustic field properties of an axisymmetric supersonic jet at both low and moderate Reynolds numbers were studied using the linear parabolized stability equations (LPSE). The results showed that, the dominant noisegeneration mechanism was determined by the characteristics of unstable wave. When Reynolds number was low, the unstable wave frequency band was relatively narrow. Since the unstable region of the disturbance wave was long along stream wise direction, the acoustic radiation region was large; the sound source was decentralized; and the radiation angle was hard to be determined. For moderately large Reynolds number, the unstable wave had a large unstable frequency wave band; the short unstable region resulted in a narrow radiation region, concentrative sound source and strong radiation directivity; and the direction angle increased with the increase of Strouhal number. The normal velocity had a negligible effect on the acoustic field for low Reynolds number, while it had to be taken into account when Reynolds number was large.
Forecasting of aeroengine performance trend based on fuzzy information granulation and optimized SVM
2017, 32(12): 3022-3030. doi: 10.13224/j.cnki.jasp.2017.12.027
Abstract PDF(914KB) icon616 icon446
Abstract:
A method to predict the change trend and space of aeroengine parameters with fuzzy information granulation (FIG) and optimized support vector machine (SVM) was put forward. FIG was adopted to granulate the parameters. Genetic algorithm (GA) was applied into adaptive selection of the best penalty parameter and kernel function parameter with Kfold cross validation (KCV) error minimum as the optimization goal. The SVM model was trained for nonlinear prediction of fuzzy particles. The verification results of some airlines monitoring performance parameters data of an aeroengine showed that the algorithm proposed can effectively realize the change trend and spatial prediction of aeroengine performance parameters. In addition, the influence of window size on prediction accuracy and the effect of multistep prediction were studied on the basis of instance. As a result, it was concluded that the best window size was three data and the forecasting error within three steps was less than 10%.
Aeroengine fault diagnosis based on IPSOElman neural network
2017, 32(12): 3031-3038. doi: 10.13224/j.cnki.jasp.2017.12.028
Abstract PDF(793KB) icon828 icon411
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An Elman neural network optimized by improved particle swarm optimization algorithm was proposed to improve the accuracy of aeroengine fault diagnosis. The input variables of the neural network were selected by MIV (mean impact value) to reduce the dimension. The improved particle swarm optimization algorithm was used to optimize the weights and thresholds of the Elman neural network, and the optimized neural network was trained. The trained neural network was used to diagnose the aeroengine fault and compared with the conventional BP（back propagation）, Elman neural networks, GM(1,n), SVM (support vector machines). The simulation results show that the diagnostic error of IPSOElman (improved particle swarm optimization Elman neural network) is smaller than other methods，and it has a good diagnosis ability and strong adaptability when the selection fault diagnosis performance parameters have changed.
μ synthesis control design of altitude ground test facilities flight environment simulation volume
2017, 32(12): 3039-3048. doi: 10.13224/j.cnki.jasp.2017.12.029
Abstract PDF(1006KB) icon547 icon405
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A μ synthesis control scheme was proposed for the control problem of flight environment simulation volume (FESV) when aeroengine was tested in altitude ground test facilities (AGTF) as well as the unmodeled dynamics uncertainty problem in the modeling process. At the same time, as for the large difference characteristic of cutoff frequency between temperature and pressure loop, the same weighted sensitive functions method was presented to solve the problem and the desired effect of simulation volume was obtained. The D-K iterative algorithm was used in the scheme to design μ synthesis controller of temperature and pressure, which can effectively solve the temperature and pressure simultaneous control design problem caused by system matrix without full rank. The different flight trajectory simulation results show that, the μ synthesis controller has good control effects for temperature and pressure of FESV. Meanwhile, the dynamic control error is less than 09% and the steady state error is less than 05%, which means the μ synthesis controller has servo tracking performance and robust performance.
Experiment on effect of gas vortex on microvibration of aerostatic bearing
2017, 32(12): 3049-3056. doi: 10.13224/j.cnki.jasp.2017.12.030
Abstract PDF(915KB) icon526 icon464
Abstract:
As a crucial element of air support system, selfexcited microvibration of gas film in aerostatic bearing could reduce the measurement accuracy and stiffness characteristics of the working system simultaneously. In order to further improve the working precision and stability of the aerostatic bearing, numerical calculation and experiment were carried out based on the study of formation mechanism of the microvibration of gas film in aerostatic bearing. The research conclusions not only verified the gas vortexs distribution law and existing pressure drop but also validated distinct zoned phenomenon of gas film along flow direction. Combined with a series of experiments to analyze the ties between intensity and location of gas vortex, main factors were summarized. The results showed that both location and intensity of the gas vortex were affected by supply pressure, inlet diameter and feed pocket structure respectively. Furthermore, the pressure fluctuation caused by pressure difference of main gas vortex was in direct relation to microvibration intensity and frequency response of aerostatic bearing.
Experiment on seal characteristics of high ratational speed of stepped labyrinth seals
2017, 32(12): 3057-3063. doi: 10.13224/j.cnki.jasp.2017.12.031
Abstract PDF(842KB) icon484 icon424
Abstract:
Experiments were carried out to investigate the seal characteristics of real size models of a typical steppedlabyrinth seal. Flow coefficients of the labyrinth seal were obtained in a high speed experiment facility at different pressure ratios (105－28), relative sealing clearances (24－40), Reynolds numbers(1900－28000) and rotational speeds (0－12000r/min).Results indicated that the flow coefficient of labyrinth seal rose with the increase of pressure ratio, and decreased with a higher relative sealing clearance. No noticeable change of flow coefficient was found when the labyrinth seal ran under a rotational speed of 5000r/min. However, under high rotational speed and low pressure ratio conditions, the flow coefficient declined more than 301% as the operating speed went up. Moreover, under the conditions with lower Reynolds numbers, a rapid drop of flow coefficient was found with the decreasing Reynolds numbers. When the Reynolds numbers were larger than 6000, no clear effect on flow coefficients can be observed. Axial pressure distribution measurements showed that pressure drop reached its minimum and maximum values when air flowed through the first and the last seal tooth respectively, the pressure dropped through the remaining teeth were almost uniform. According to the findings, an empirical expression to evaluate flow coefficients of steppedlabyrinth seals was also obtained, and agreed with the experimental results perfectly.
Multiobjective optimization of incidence features for cascade
2017, 32(12): 3064-3072. doi: 10.13224/j.cnki.jasp.2017.12.032
Abstract PDF(911KB) icon534 icon423
Abstract:
MultiBezier curve was adopted to describe the cascade of the axial flow compressor in parameterized form. By taking the Isight software as optimization platform, the calculation program of the S1 surface was adopted to calculate the flow field, and the improved nondominated sorting genetic algorithm (NSGAⅡ) was employed to conduct the multiobjective optimization of the features of incidence for the cascade of the middle section of rotor and stator of Stage35, which was onestage axial flow transonic compressor from NASA. The optimization goal was to reduce the total pressure loss coefficient in the whole range of the incidence and widen the adaptive range of the incidence. The lowest total pressure loss coefficient and the difference between the relatively highest and the lowest point of total pressure loss coefficient were set as the optimization objective functions. The flow rate of the cascade constant was set as constraint. Results indicated that the optimization greatly reduced the total pressure loss coefficient of the cascade of the middle section of rotor and stator, and widened the range of the incidence of the middle section of rotor and stator by 5° and 3° respectively.

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