2018 Vol. 33, No. 12

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Test technique of aerodynamic parameters measurement during icing/de-icing process under icing environment
2018, 33(12) doi: 10.13224/j.cnki.jasp.2018.12.001
Abstract PDF(1212KB) icon930 icon558
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Aerodynamics parameters measurement of the cylinder was studied in the secondary test section of 0.3m×0.2m icing wind tunnel during icing/de-icing process. The electrothermal cylinder model and five-component external balance for low temperature and high humidity environment were established. The variation of aerodynamics force/moment on cylinder was studied during icing/de-icing process under icing meteorological environment. The influence of spraying on loading and dynamic pressure can be ignored. The increments of maximum horizontal force and dynamic pressure on cylinder in unit time were 0.6% and 0.2%, respectively. The aerodynamics force measurement technique for low temperature and high humidity environment can capture the variation of aerodynamics force/moment during icing/de-icing process. The variation of resistance coefficient of cylinder became larger and larger, showing an approximately linear increasing trend during icing process. And the variations of lift, pitching, yawing and rolling coefficient were small, which can be ignored. The ice shell slippage on the leading edge changed the position during de-icing process, resulting in the fast variation of resistance, yawing and rolling coefficient. Further it would bring about unpredictable influence on aerodynamics performance.
Experiment and factors affecting ethylene ignition in supersonic flow-field
2018, 33(12) doi: 10.13224/j.cnki.jasp.2018.12.002
Abstract PDF(1821KB) icon861 icon607
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The non-premixed ethylene ignition in supersonic flow-field was experimentally conducted to obtain the events of successful/failed flame propagation and the evolution of shock wave train during ignition transient using high speed photography and schlieren method. The key flow characteristics such as fuel distribution, length of recirculation zone, effect of shock wave train and air throttling affecting flame development and the modes of flame extinguishment were analyzed with the measurement of NPLS (nano-particle-based planar laser scattering) and PIV (particle image velocimetry) technology by combing with large eddy simulation data. The results showed that the shock train was pushed forward during the process of flame initiation leading to the fuel mass fraction difference between the conditions before and after ignition. The recirculation zone trapped in the fore corner of cavity was essential to the creation of initial flame, in which the ignition energy accumulated and the flame expanded and transported downstream until cavity trapped flame and positive feedback was built up. The fuel distribution within cavity was influenced by the position and pressure of fuel injection and can be accommodated by direct injection within cavity, which was beneficial for the initial flame kernel propagation while avoiding extinguishment caused by feedback.
Experiment on flow instability of aviation kerosene under supercritical pressures
2018, 33(12) doi: 10.13224/j.cnki.jasp.2018.12.003
Abstract PDF(825KB) icon903 icon568
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Experimental study on flow instability of aviation kerosene under supercritical pressure in a vertical upward circular tube was conducted. The time-dependent inside-wall temperature, mass flux, outlet temperature and inlet-outlet pressure drop oscillations were investigated. The formation reason and feedback mechanism of flow instability were expounded. The expression for critical heat load prediction of flow instability was obtained. Results indicated that the abnormal fluctuations of inside-wall temperature and inlet-outlet pressure drop occurred under the flow instability conditions. The flow instability was caused by a gas-like state film, owing to the deteriorated heat transfer during the development process of boundary layer. Two types of feedback mechanism were found. On the one hand, the deteriorated and enhanced heat transfer appeared alternately due to the pseudo-film boiling and pseudo-nuclear boiling, which led to the thermal instability. On the other hand, the pressure disturbance triggered the acoustic wave, the compressed wave made a decrease in thickness of gas-like state film, and enhanced the heat transfer, while the expandsion wave made an increase in thickness of gas-like state film, and weakened the heat transfer, leading to the acoustic wave instability. The comprehensive effects of these two feedback mechanisms cause the thermo-acoustic oscillation phenomenon.
Application of γ-Reθt transition model in investigation of flow characteristics in microchannel
2018, 33(12) doi: 10.13224/j.cnki.jasp.2018.12.004
Abstract PDF(678KB) icon936 icon570
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Numerical investigation was conducted with ANSYS CFX to investigate the flow characteristics in a rectangular microchannel. The performance of laminar model, γ-Reθt transition model and shear stress transport model in microchannel transition simulation was examined by comparing the predicted results with the experimental data. Furthermore, the effects of length-to-diameter ratio and aspect ratio were also investigated. Results indicated that only the γ-Reθt model predicted the trend of transition and forecasted a critical Reynolds number close to the experimental result. Length-to-diameter ratio over 200 was suggested to eliminate the influence of the entrance effect. The critical Reynolds number increased when the aspect ratio varied from 1 to 5.
Effect of hydrogen volume fraction on combustion instability of hydrogen/methane premixed flame under different equivalence rates
2018, 33(12) doi: 10.13224/j.cnki.jasp.2018.12.005
Abstract PDF(825KB) icon1205 icon562
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The combustion instability of premixed bluff-body flame under acoustic excitation at different equivalence rates (0.8, 1.0, 1.2) and hydrogen volume fraction (0, 10%, 20%) was analyzed. The combustion instability could be captured by the flame transfer functions and the flame front distribution could be shown by CH chemiluminescence measurement. Results showed that the combustion characteristics were very sensitive to the fraction of hydrogen in the fuel mixture. When equivalence rates were 0.8 and 1.0, the amplitude of flame transfer functions and heat release fluctuations increased with hydrogen concentration. And with the increase of hydrogen concentration, the combustion instability of premixed flame became stronger. When hydrogen volume fraction increased at equivalence rate of 1.2, the amplitude of flame transfer functions firstly reduced then increased.
Numerical simulation of effect of turbulence flow in nozzle on flame lift-off length
2018, 33(12) doi: 10.13224/j.cnki.jasp.2018.12.006
Abstract PDF(850KB) icon800 icon596
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In order to consider the effect of turbulence inside the nozzle on fuel spray and flame lift-off length, the turbulence was characterized by the length scale and time scale and added into primary breakup model in the form of weight coefficient, and the secondary breakup process was modified. A mathematical model of fuel spray and combustion was established. The mathematical model was validated by experimental data, and the effect of turbulence term on fuel spray was analyzed. Results indicated that the turbulence term can accelerate the rate of droplet breakup and evaporation, decrease the fuel vapor penetration. The calculation of the flame lift length was based on the fuel atomization model. These models can well predict the flame lift-off length at different conditions of oxygen volume fraction, ambient density, ambient temperature and injection pressure. It also can be found that the effect of turbulence inside the nozzle on flame lift-off length was 9% and 13% at different ambient density and oxygen volume fraction conditions, and the injection pressure and ambient temperature could enhance the influence of turbulence inside nozzle on flame lift-off length.
Effects of thermodynamic on unsteady cavitation flow of liquid hydrogen
2018, 33(12) doi: 10.13224/j.cnki.jasp.2018.12.007
Abstract PDF(1282KB) icon859 icon566
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In order to investigate the effects of thermodynamics on the unsteady cavitation flow of cryogenic fluid, the unsteady cavitation flow of the liquid-hydrogen around the Ogive body was studied by using the large eddy simulation under thermodynamics and isothermy. The results showed that the thermodynamics prolonged the cavitation period of liquid hydrogen, enhanced the unsteady characteristics and suppressed the cavitation. In addition, compared with isothermy, the cavitation in thermodynamics containd finer bubbles. A temperature depression about 1.5K was detected because of thermodynamics. Besides, the vortex structure moved from the cavity interface to the inner of the cavity due to the thermodynamics. The interaction between cavitation and vortex structure was also studied based on the vorticity transfer equation under thermodynamics and isothermy. In thermodynamics, the vortex stretching term is mainly located at the front and the end of the cavity, and the vortex dilation term and baroclinic torque term are mainly located inside the cavity. In isothermy, the vortex stretching term and vortex dilation term are mainly located at the interface of cavity, and the baroclinic torque term is located at the end of cavity.
Experiment on evaporation efficiency of vaporizer andnumerical simulation of two-phase flow in vaporizer
2018, 33(12) doi: 10.13224/j.cnki.jasp.2018.12.008
Abstract PDF(1028KB) icon1165 icon640
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To study the atomization and evaporation charactertistics of rear intake vaporizer, the experiment researched the influences of intake temperature, air fuel ratio (AFR), wall temperature and inlet air velocity on evaporation efficiency. Result of the experiment showed that intake temperature and inlet air velocity were two major factors influencing evaporation efficiency; when AFR decreased to 3.0, the flow pattern transformed from film boiling to transition boiling, now heat efficiency was the lowest. Discrete phase model (DPM) and droplet splashing model were employed to simulate the two-phase flow in the vaporizer. Calculation of evaporation efficiency was in reasonable agreement with experimental data. The numerical results show that the increase of inlet air velocity can improve the atomization quality, but it is not conducive to the uniformity of droplet distribution. Sauter mean diameters（SMD） is proportional to the -1.69 power of inlet air velocity.
Review on methods of aircraft engine nonlinear aerothermal-dynamic modeling for airworthiness requirement
2018, 33(12) doi: 10.13224/j.cnki.jasp.2018.12.009
Abstract PDF(1467KB) icon939 icon553
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The requirement and progress of aircraft engine nonlinear aerothermal-dynamic modeling technique for the surge phenomenon and rain and hail ingestion effects in special operating conditions were reviewed pursuant to airworthiness regulation. Key modeling elements for the model with the simulation capability of surge, rain ingestion and hail ingestion were proposed based on the analysis of aero-engine dynamic characteristics and transient simulation methods. Result showed that, rotor dynamics was the most important compared with volume dynamics and thermal effect. Constant flow method had high accuracy and inter-component volume method was suitable for description of the engine high frequency dynamics. Compliance demonstration model should incorporate surge, rain ingestion and hail ingestion elements based on the component-matching aerothermal-dynamic model. The analysis can support the simulation tools development based on test data and service data.
Experiment on flow mechanism and aerodynamic interaction characteristics of tilt-rotor aircraft
2018, 33(12) doi: 10.13224/j.cnki.jasp.2018.12.010
Abstract PDF(1794KB) icon1340 icon601
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With use of experimental methods, aerodynamic interactional characteristics between rotor and wing of a tilt-rotor aircraft were measured both in hover and transition modes, partly revealing the interactional flow mechanism. The shrinking of rotor downwash was found to be more intense and roll-up vortex was more severe, in its large collective pitch states compared with the small one, based on the result of flow measurement via 3D-PIV (particle image velocimetry) technology. The generation mechanism of “fountain effect” was revealed and the position of “fountain” center influenced by the induced effect of rotor, varied visibly with the changes of collective pitch and the interval between rotor and wing. Then the aerodynamic interactions between rotor and wing in different configurations and state parameters were measured, and during the measurement, tilt-rotors lift was found to be increased either by reducing the vertical or horizontal distances of wind and rotor, bringing to wing the increasing downloads at the same time. A particular configuration at last was selected to perform an interaction experiment in its transition mode to obtain the relationship between the comprehensive aerodynamic characteristics of wing, rotor and the angle of attack of the wing. It is shown that, in large angles of attack of the wing, the encumbering effect of the wing on rotor downwash, acting as a lift-promoting effect on the rotor like “ground effect”, is promoted, but this effect is enervating with the turning of the wing; and the wing lift tends to go up firstly then down with the increase of the wing angles of attack.
Aero engine sand dust ingestion electrostatic monitoring simulation experiment
2018, 33(12) doi: 10.13224/j.cnki.jasp.2018.12.011
Abstract PDF(1291KB) icon887 icon556
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A simulation experiment method for electrostatic monitoring of aero engine dust ingestion was proposed. Based on ANSYS electromagnetic field analysis module, a finite element model was established, the electrostatic induction signals of sand dust ingestion under different particle sizes, charge-mass ratios, moving speeds and mass concentrations were simulated experimentally, and the induced charge and voltage signals were analyzed from the time domain and frequency domain, respectively. The relationship between particle size and other macroscopic parameters of sand ingestion and electrostatic monitoring signals was studied to establish a characteristic index used to characterize the particle size of sand dust particles. The eigenvectors were established based on the power spectral density distributions of the IDMS(ingested debris monitoring system) induced voltage signals. The Manhattan distance and the Euclidean distance were used as characteristic indicators to characterize the sand particle size. Simulation results showed that the characteristic index was positively correlated with sand dust particle size, and it was not affected by the movement velocity and charge-mass ratio of sand ingestion, but affected by the sand dust ingestion mass concentration. Further studies will use quality concentration to correct the characteristics of the indicators and carry out verification experiments.
Analysis on the force measurement accuracy of the integrated vehicle in the impulse wind tunnel
2018, 33(12) doi: 10.13224/j.cnki.jasp.2018.12.012
Abstract PDF(703KB) icon732 icon529
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To evaluate the force measurement accuracy of the integrated vehicle in the impulse combination wind tunnel, some actions were taken. Firstly, the force-measurement system was simplified and the dynamic equation was built according to its structural characteristics. Then, the impulse response attenuation function was deducted. Secondly, the time-dependent changing rule of the output signal of the force-measurement system was analyzed and the dominant frequency of was acquired through fast Fourier transformation (FFT) method. Next, the neural network algorithm and gradient descent algorithm were used to fit the signal of force balance and to predict the trend value of the force-measurement signal. Finally, the signal fitting and trend prediction of a number of tests data were conducted and the measurement accuracies were acquired. The result prove that this method can truly predict the stable output result, meanwhile, the measurement accuracy can reach over 97% when the output signal of force-measurement system includes 4 cycles.
Unsteady flow field and flow-induced noise analysis forexpansion chambers based on hybrid method
2018, 33(12) doi: 10.13224/j.cnki.jasp.2018.12.013
Abstract PDF(1093KB) icon843 icon420
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The unsteady flow field and flow-induced noise of the expansion chamber under the effect of airflow were numerically simulated and analyzed based on hybrid method. The simulation model based on the finite volume method was established, and the large eddy simulation method was used to calculate the unsteady flow in the expansion cavity. The numerical simulation successfully captured the unsteady flows and the development of eddies in the internal cavity, and agreed well with the experiment results. The flow field results were inserted into acoustic mesh by the integral interpolation method, and then the flow-induced noise sources were calculated by the aeroacoustics theory. The flow-induced noise sources were imported to the acoustic simulation model to calculate the sound pressure at the response points. The acoustic simulation results agreed well with the experiment results on the sound pressure level and resonance frequencies. The results showed that the hybrid method combined the large eddy simulation and the aeroacoustics theory, and revealed the mechanism and process of the flow-induced noise generation in the expansion chamber accurately. The deviations of the tail pipe radiated noise between the simulation results and the experimental results, as well as the theoretical calculation results, were within 5%.
Simulation of windmilling-ram mode performance for tandem TBCC engine
2018, 33(12) doi: 10.13224/j.cnki.jasp.2018.12.014
Abstract PDF(1256KB) icon888 icon482
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The windmilling-ram mode performance simulation model was developed for a tandem turbine-based combined cycle (TBCC) engine based on the matching of the component low-speed characteristics. Extrapolation method for the compressor characteristics at low-speed and high flow region was proposed, and the issues associated with the component efficiency discontinuity at low speeds were solved through substitution of isentropic efficiency by corrected torque while describing the characteristics map of rotational component. Influence of ram bypass area variation and turbine power offtake on the windmilling-ram mode performance and component matching was analyzed, and parameter regulating laws during mode transition, including the windmilling-ram mode, were investigated based on the smooth variation of engine thrust and airflow. The simulation results showed that: under the windmilling-ram mode, the fan operation was strongly related to the ram bypass area variation, exerting a relatively small influence on the compressor operation; with the increase of the windmilling spool speed, turbine power offtake first rose and then dropped, and the specific impulse was linearly reduced with the increase of turbine power offtake, while the power offtake location of high-pressure or low-pressure turbine had a significant influence on the component matching.
Experiment on active control of low frequency in-plane harmonic noise for electrically controlled rotor
2018, 33(12) doi: 10.13224/j.cnki.jasp.2018.12.015
Abstract PDF(894KB) icon747 icon465
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In order to reduce rotor low frequency in-plane harmonic noise, a noise measuring system and a control system were developed accordingly and a frequency-domain active control method was proposed based on the integrated test rig of electrically controlled rotor(ECR). Then the close-loop active control experiments of low frequency in-plane harmonic noise using ECR were performed in hover state. During the experiment, the control frequency of the flap was 10Hz, the noise signal captured by the microphone in plane was used as feed-back signal and the noise signals captured by the other two microphone were used for monitoring. At the same time the vibration lever of the hub was monitored. After control, the control system took 5s to enter into a steady state, the convergence speed was fast and there was no obvious overshoot during convergence. 9.4dB noise reduction was possible at the location of the microphone in plane, and the vibration level of the hub increased a little. Experiment results showed that the developed control system was effective and reliable in reducing low frequency in-plane harmonic noise through the tests, and the feasibility and effectiveness of the frequency-domain active control algorithm in reducing low frequency in-plane harmonic noise were validated.
Prediction and experiment of vibration wear of aviation spline
2018, 33(12) doi: 10.13224/j.cnki.jasp.2018.12.016
Abstract PDF(764KB) icon989 icon537
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The relative motion displacement between the teeth of aviation spline under vibration condition was deduced based on the Archard wear theory. The wear of experimental spline was predicted with consideration of the cycle of working conditions and the vibration displacement, and the aviation spline wear experiment rig was set up. Theoretical prediction indicated that wearing capacity linearly increased with the wear coefficient and transmitted torque, decreased with the tooth number and hardness, and nonlinearly increased with the vibration. The experimental results were in good agreement with the simulation results, but the results had a certain fluctuation at the wear initial stage and a certain deviation at the wear later stage, owing to the deviation of spline manufacturing and installation, simplification of theoretical model and the complex working conditions of spline. Vibration has a decisive influence on spline wear, so it is necessary to control the rotor amplitude of internal and external spline and improve the dynamic balance level of spline rotor design, which can effectively reduce spline wear.
Experiment on thermomechanical fatigue in nickel based single crystal superalloy DD6
2018, 33(12) doi: 10.13224/j.cnki.jasp.2018.12.017
Abstract PDF(1436KB) icon974 icon533
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According to the service loads experienced by air cooled single crystal turbine blades, thermomechanical fatigue (TMF) experiments were designed and conducted on thin-walled tube specimens made of nickel based single crystal superalloy DD6. The results indicated that the deformation response of DD6 exhibited remarkable ratcheting effect, which was closely related to the phase angle and mechanical loading; and the lifetime of in phase (IP) TMF under all experiment conditions were shorter than that of out of phase (OP) TMF. Either introducing dwell time at peak temperature or increasing mechanical load led to more ratcheting strains and fewer failure cycles. Based on the metallographic examination on fracture surface and longitudinal section of specimens, the critical life-limiting factors under different load conditions were identified. Creepage and fatigue dominate in the competing damage mechanisms for IP TMF, while oxidation and fatigue dominate for OP TMF.
Effect of mean stress on multiaxial fatigue failure of 30CrMnSiA steel
2018, 33(12) doi: 10.13224/j.cnki.jasp.2018.12.018
Abstract PDF(849KB) icon958 icon471
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Fatigue experiments were carried out to investigate the effects of mean-stress and phase-difference on the tension-torsion fatigue life of 30CrMnSiA high strength steel, while the experimental data and plane stress characteristics of different mean stress and phase difference were analyzed. The test results showed that the fatigue life increased with the growing phase difference without mean stress, but decreased with the increase of phase difference when mean stress existed, whether mean normal stress or mean shear stress. Criteria based on the linear combination of the shear stress amplitude and normal stress on the maximum shear stress amplitude plane cannot reflect the test results correctly to some degree. Moreover, the initial crack angle was measured showing that its direction was close to the maximum shear stress amplitude plane. Finally, the defects of the criteria based on the linear combination shear stress amplitude and maximum normal stress on the maximum shear stress amplitude stress plane were explained by stress analysis.
Influence of fluid inertia on dynamic characteristics of elastic ring squeeze film damper-rotor system
2018, 33(12) doi: 10.13224/j.cnki.jasp.2018.12.019
Abstract PDF(1311KB) icon1003 icon474
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The inner and outer oil film distribution pressure and resultant force of elastic ring squeeze film dampers(ERSFD) were calculated through the generalized Reynolds equation with the effect of fluid inertia by finite difference method, and used to analyze the dynamic of ERSFD-rotor system. Comparing oil film pressure, oil film resulant force and the rotor amplitude-frequency of the rotor systems with/without fluid inertia, it was found that when the Reynolds number was large, there was significant difference between them. The equivalent stiffness and damping were larger, the critical speed was bigger and the amplitude was smaller in the resonance zone when the fluid inertia was calculated. When the rotor speed is bigger or the viscosity is smaller and the Reynolds number is larger, it is necessary to consider the effect of fluid inertia in calculation of oil film force.
Curved blade three-dimensional operational deflection shape continuous scanning laser measurement
2018, 33(12) doi: 10.13224/j.cnki.jasp.2018.12.020
Abstract PDF(860KB) icon848 icon483
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A continuous scanning laser Doppler vibration measurement method for three-dimensional operational deflection shape of a curved blade was proposed and applied to vibration test of a compressor blade. The image geometric transformation was introduced into the laser continuous scanning measurement, and a laser continuous scanning path algorithm capable of dealing with irregular geometries of curved blades was developed. The continuous scanning laser vibration test was applied to non-rectangular area, and its accuracy was verified by test. Based on this method, the approach for measuring three-dimensional operational deflection shape of curved blades was taken, and the coordinate decomposition principle of three-dimensional laser test was studied. The three-dimensional laser continuous scanning test was performed on a compressor blade and the first nine modes within 3600Hz were obtained. The correlation with the results from the commercial three-dimensional laser discrete scanning modal test was basically above 0.95, demonstrating the feasibility and accuracy of three-dimensional continuous scanning laser Doppler vibration test. The continuous scanning laser Doppler vibration measurement, with advantages of high spatial resolution, efficient and effective test, shows the practical value for further engineering application.
Acoustic performance of piezoelectric acoustic liners with heteromorphic cavity
2018, 33(12) doi: 10.13224/j.cnki.jasp.2018.12.021
Abstract PDF(869KB) icon841 icon471
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In order to improve the suppression range of the low frequency noise of the piezoelectric acoustic liners, the structure of the acoustic liner was optimized. By using the plane wave theory, the acoustic physical model of two kinds of curvilinear channels was constructed, and the transfer matrix of two models was established, which can be used as the theoretical basis for loss calculation of the Helmholtz resonator of the heteromorphic cavity; and the correctness was verified by simulation. Combining the deformation of the piezoelectric oscillator with the finite element simulation analysis of the acoustic liner, the results showed that under the condition of applying 500V driving voltage to the piezoelectric oscillator, the two kinds of acoustic systems were offset by 115Hz and 120Hz, respectively. Compared with cylindrical cavity acoustic liner, the results show that: within the same cavity thickness range, for the cavity generated by the curve of greater curvature under the condition of the same driving voltage, the frequency variation is higher, thus providing an effective basis for the acoustic liner cavity structure optimization.
Low cycle fretting fatigue tests of dovetail structure at elevated temperature
2018, 33(12) doi: 10.13224/j.cnki.jasp.2018.12.022
Abstract PDF(878KB) icon883 icon472
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A kind of elevated temperature fretting fatigue test device of dovetail structure was designed for the compressor fan/disk connection structure of aviation turbofan engine. The fretting fatigue tests of TC11 titanium alloy at 200℃ and 500℃ were carried out. The monitoring of the initiation life of dovetail fretting fatigue was achieved by dynamic displacement method and dynamic strain method. It was found that the fretting fatigue cracks were at the lower edge of the contact area of the dovetail and a large amount of abrasive scrap appeared on the contact surface as a typical fretting fatigue failure. The test results show that the effect of temperature environment on fretting fatigue life is obvious. With the increase of the test temperature, fretting fatigue life of the test specimen will gradually decrease.
Research on quality achieving reliability of bearing based on fuzzy weight
2018, 33(12) doi: 10.13224/j.cnki.jasp.2018.12.023
Abstract PDF(781KB) icon814 icon442
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Based on the theory of fuzzy mathematics, the method to determine the weight of bearing quality influencing factors was put forward. The original model of quality achieving reliability was modified and the improved model of bearing quality achieving reliability was proposed. Then the true value and true value interval of bearing quality achieving reliability were further estimated based on the maximum entropy principle. Taking two kinds of tapered roller bearing, 30306 and 30204, as experimental objects, it was found that the deviation of the original reliability model calculation from the test results was 20%-35%, and the deviation of the improved reliability model calculation from the test results was 12%-14%, which was reduced by 8%-21%. It can be known that the improved reliability model is more accurate than the original reliability model.
Static and dynamic performance of laminated gas foil thrust bearing
2018, 33(12) doi: 10.13224/j.cnki.jasp.2018.12.024
Abstract PDF(1042KB) icon772 icon446
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Analytical model was presented for a novel laminated gas foil thrust bearing. The performance of this thrust bearing was studied by coupling the foil deformation equation and the compressible gas-lubricated Reynolds equation solved by finite difference method(FDM). Due to the variable stiffness characteristic in radial direction and circumferential direction of supported foils, the second wedging effect phenomenon and two pressure peaks were found, and the load capacity was improved compared with traditional gas foil thrust bearings. Bearing load capacity, friction torque and dynamic stiffness all declined with the decrease of minimum film thickness, but dynamic damping changed very little. There was optimum height of wedge to obtain higher load capacity and lower torque, which reduced the loss. Meanwhile, higher dynamic stiffness and higher dynamic damping can be achieved at the optimum height of wedge.
Analysis of flow field characteristics of medium reducer with splash lubrication in a certain helicopter
2018, 33(12) doi: 10.13224/j.cnki.jasp.2018.12.025
Abstract PDF(1122KB) icon742 icon436
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For the purpose of analyzing the characteristics of the internal flow field of middle reducer with splash lubrication in a certain helicopter, based on the computational fluid dynamics (CFD) method, a numerical simulation model for the splash lubrication of middle reducer, including gear box housing, spiral bevel gear and oil guide device, was established by using the volume of fluid (VOF) multi-phase flow model and the turbulence model. With these models, the flow field characteristics of splash lubrication were obtained, and the transient flow field of lubricating oil in reducer was visualized; the influence of gear speed and oil immersion depth on the flow of lubricating oil in key positions was analyzed. Results showed that the oil flow in gear meshing zone was positively correlated with the gear speed and the depth of oil immersion. The oil flow in the oil guide pipe was related to the oil saturation value of the oil guide device. When the oil quantity was greater than this value, the oil flow in the oil guide pipe increased with the increase of the gear speed, and remained constant with the increase of the oil immersion depth. A splash lubrication test system of spiral bevel gearbox was set up, and results of oil flow tests of round hole in the process of splash lubrication were compared with the corresponding simulation results, the maximum error of simulation results relative to experiment was 9.5%, verifying the correctness of the simulation method.
Design method of acoustic liner applied toaft-fan noise reduction and experimental validation
2018, 33(12) doi: 10.13224/j.cnki.jasp.2018.12.026
Abstract PDF(736KB) icon906 icon468
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Liner design method applied to aft-fan noise reduction was implemented.The design phases were separated into two parts. In the first phase, an empirical impedance model was adopted to get the preliminary design. In the second phase, an optimization procedure was performed by numerical simulations based on high-order computational aeroacoustic method to achieve the optimal acoustic impedance and corresponding geometry parameters.In order to validate the method, an experimental investigation of aft-fan noise was carried out in the anechoic chamber of Beijing University of Aeronautics Astronautics.The fan noise source was modeled by a mode source generated by speakers.The circumferential mode was 1 and the radial mode was 0, the frequency was 3150Hz.The Mach numbers were 0.8 and 0.6 for the core and bypass ducts respectively. Experimental results showed that the preliminary design had 10dB insertion loss and the optimized liner achieved 3-4dB more attenuation.
Experiment on effects of slotted tailboard on flow field of transonic turbine linear cascade
2018, 33(12) doi: 10.13224/j.cnki.jasp.2018.12.027
Abstract PDF(996KB) icon834 icon379
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Numerical and experimental investigations were performed to study the effect of the slotted tailboard on the periodicity of transonic gas turbine cascade. Computational fluid dynamics was employed to study the effect of tailboards for pressure distributions of the blades and cascade passage exits with different void ratios (10%, 15%, 30%, 50%) and pitch angles (70°, 71°, 72°), meanwhile experiment was performed to verify that the tailboard improved the periodicity of cascade passage exit flow field. Results showed that, without tailboard, pressure distributions of the blades deviated from the periodic result apparently and the periodicity error of the cascade passage exits was quite large. Pressure distributions were affected by tailboards with different void ratios and pitch angles, besides, the periodicity of the flow field can be improved with a tailboard of appropriate parameters. Pressure distributions of cascade passage exits were much closer to each other and the periodic result with void ratio of 50% and pitch angle of 70° tailboard when compared with no tailboard condition, while the periodicity errors of numerical and experimental results were reduced by 47.6% and 28.1%, respectively.
Experiment for hydraulic vibration onrocket engine feed pipe-Venturi tube system after pump
2018, 33(12) doi: 10.13224/j.cnki.jasp.2018.12.028
Abstract PDF(965KB) icon896 icon397
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In order to investigate the dynamical characteristics of the feed pipe - Venturi tube system after pump in a liquid rocket engine, hydraulic vibration experiment were conducted. By generating hydraulic vibration signal after Venturi tube, the pressure fluctuation data at the feed pipes and the thrust chamber manifold were measured, and the transfer function for disturbing this system dynamics was established. The test results indicated that the first resonant response was the main characteristics for the feed system, and the high order resonant peak was unobvious. At the resonant frequency, the pressure oscillation amplitudes were quite high between Venturi tube and main valve, and increased along the flow direction before main valve, but decreased after main valve. A phenomenon of pressure fluctuation transmitting upstream through Venturi tube was discovered. Even the Venturi tube was under the cavitation condition, partial pressure fluctuation could transmit upstream through it, while the Venturi tube also had an evident insulated effect for the whole feed pipe. When the cavitation allowance of Venturi tube was excessively big, the Venturi tube outlet condition was changed from acoustic closed boundary to acoustic open boundary.

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