2016 Vol. 31, No. 2

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Effect of low cycle fatigue pre-damage on high cycle fatigue strength of TA11 alloy
SHI Duo-qi, LUO Yin-yin, ZHAO Peng-tao, YU Hui-chen, YANG Xiao-guang
2016, 31(2): 257-265. doi: 10.13224/j.cnki.jasp.2016.02.001
Abstract PDF(990KB) icon1304 icon522
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The effect of pre-damage of low cycle fatigue (LCF) on high cycle fatigue (HCF) strength of TA11 alloy was experimentally investigated. Three factors were considered, including cyclic max stress, stress ratio and the life ratio in LCF experiment. The effect of LCF pre-damage on high cycle fatigue strength of standard specimen was obtained using rotation bending fatigue experiment according to a step-by-step procedure. Result shows that the previous LCF cycles with the max stress of 900MPa generate a larger cyclic plastic strain. Therefore, even applying few LCF pre-damage can still reduce the HCF strength. Different stress ratios of LCF pre-damage will reduce the HCF strength. For different max stress in LCF pre-damage, when the LCF pre-damage max stress is far lower than the yield strength, it has less effect on the HCF strength. However, the effect on TA11 alloy must be considered when the LCF pre-damage max stress is close to or greater than the yield strength.
Experiment on electric discharge machining of cooling holes in superalloy IN718
GUO Yong-feng, ZHANG Guo-wei, WANG Li, GUO Ben-sheng
2016, 31(2): 266-273. doi: 10.13224/j.cnki.jasp.2016.02.002
Abstract PDF(772KB) icon1243 icon513
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Processing methods of electrical discharge machining (EDM) using inner jet liquid rotating electrodes under the kerosene liquid about ø0.5mm small holes on superalloy IN718 was proposed. The effects of process parameters of EDM, such as peak current, pulse on time, duty cycle and hydraulic pressure, on the material removal rate and the electrode relative-wear were studied using orthogonal design. Comprehensive formula about the material removal rate and the electrode relative-wear based on orthogonal experiment was established to choose the best processing parameters. The analysis of the results shows that the influence of peak current on the material removal is most obvious followed by the hydraulic pressure and duty cycle. The influence of pulse on time on the material removal rate is not significant; the influence of peak current on the electrode relative-wear is most obvious, followed by the hydraulic pressure. The influences of the pulse on time and the duty cycle on the electrode relative-wear are not significant; the optimization parameter group is the peak current 8A, pulse on time 130μs, duty cycle 0.35, and hydraulic pressure 5MPa. This is the optimum parameter group obtained by experimental study.
Assessment method of structural efficiency on bearing system in aero-engine
MA Yan-hong, CAO Chong, LI Xin, HONG Jie
2016, 31(2): 274-281. doi: 10.13224/j.cnki.jasp.2016.02.003
Abstract PDF(787KB) icon1765 icon533
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Targeting the structural and mechanical characteristics of aero-engine bearing system, a structural efficiency evaluation method was proposed based on the system's structural function and design requirements. Stress distribution coefficient, vibration equivalent specific stiffness, stiffness sensitivity to temperature, and isolation coefficient were used to assess the bearing capacity, resistance to deformation and dynamic environment adaptability of the structure. A structural efficiency assessment on two design schemes of the turbine inter-stage bearing frame for turbopropeller engine was conducted. Result indicates that the structural efficiency of design A is 39.6% greater than design B. Those assessment parameters are at a reasonable level, and can quantitatively reflect the advantages and disadvantages of two schemes. The result proves the validity of the assessment method.
Theoretic investigation on vibration characteristics of structure with air film damper
ZHANG Da-yi, HE Yi-feng, CHEN Lu-lu, MA Yan-hong, HONG Jie
2016, 31(2): 282-288. doi: 10.13224/j.cnki.jasp.2016.02.004
Abstract PDF(792KB) icon1399 icon526
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According to the configuration design requirements of the air film damper in the aero engines, the mechanics model of the air film damper was built based on the extrusion gap flow theory and energy equation. Therefore, the equivalent stiffness coefficient and the equivalent damper coefficient were obtained. The amplification factor's expression was also obtained through derivation from the vibration equations. Research results revealed that,the air cavity thickness, the initial cavity pressure, the modal frequency and the location of the absorbing vibration plate were the key parameters which determined effect of vibration reduction. The optimization air cavity thickness was determined by the boundary layer thickness and vibration frequency, thus the best value could be acquired according to the particular case in order to depress the vibration response to the maximum extent. The damper coefficient increased with the increase of the initial cavity pressure. The nature frequency of the additional plate was recommended to be close to that of blade, and the absorbing vibration plate was suggested to be installed on the location with the maximum vibration response,in order to obtain the best effect of vibration reduction.
Crystallographic-orientation-related performance of single crystal turbine blade and optimization design of three-dimensional orientations
GAO Jing-yun, FANG Lei, ZHANG Cheng-cheng, REN Yuan, LI Ying
2016, 31(2): 289-298. doi: 10.13224/j.cnki.jasp.2016.02.005
Abstract PDF(962KB) icon1483 icon523
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Based on orthotropic elasticity constitutive model, the influence of three-dimensional crystallographic orientations on the performance of single crystal turbine blade was analyzed. It was shown that three-dimensional crystallographic orientations obviously affected maximum stress, creep life, low-cycle fatigue life and maximum radial displacement on blade top surface. Moreover, three crystallographic angles coupled together. The influence of the deviation angle or one of the random angles changed with the varying orientations of the other two. The orientations optimization was performed in ISIGHT platform with creep life, low-cycle life and maximum radial displacement on blade top surface set as optimization objectives. The neighborhood cultivation genetic algorithm was used to get the Pareto optimal solution set. All Pareto solutions focused within range of the deviation angle about 12 degrees. The Pareto solution with maximum life was chosen as the optimized solution, so the creep life and low-cycle fatigue life increased up to 6 times and 37 times of the original design point, and the maximum radial displacement on blade top surface reduced by 2.5 percentage, respectively.
A thermo-mechanical fatigue life assessment method for single crystal turbine blades
JING Fu-lei, WANG Rong-qiao, HU Dian-yin
2016, 31(2): 299-306. doi: 10.13224/j.cnki.jasp.2016.02.006
Abstract PDF(977KB) icon1633 icon561
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A thermo-mechanical fatigue (TMF) life assessment method of single crystal turbine blades was developed based on TMF experiments of single crystal turbine blades combined with deformation and damage theory of single crystal as well as numerical simulation for thermo-mechanical fatigue problem of single crystal turbine blades. Firstly, the cyclic stresses and temperatures generated on the critical section in the single crystal turbines during service were simulated with the TMF experimental system of hollow air-cooled turbine blades, and the position of crack initiation and the TMF life were determined. Then, the Walker viscoplastic constitutive model based on slip systems and cyclic damage accumulation (CDA) model based on critical plane were proposed considering the features of deformation and damage behavior of single crystal turbine blades. Finally, the numerical simulation of TMF of single crystal turbine blades under the experimental conditions was performed with the above-proposed constitutive model and life model. Results show that the theoretical dangerous point is consistent with the experimental results, and the calculated life is basically within three times scatter band of the experimental life.
Study on imbalance-fixed point rubbing coupling faults of dual-disc cantilever rotor
YANG Yang, CAO Deng-qing, WANG De-you, JIANG Guang-yi
2016, 31(2): 307-316. doi: 10.13224/j.cnki.jasp.2016.02.007
Abstract PDF(1066KB) icon1350 icon536
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The dynamic model for a dual-disc cantilever rotor system with imbalance-fixed point rubbing coupling faults was established. In the coupling model, the rubbing force of fixed point rubbing was characterized by nonlinear hysteretic force model. In the process of numerical simulation, the moment of rubbing happening was estimated by linear interpolation method. The results of numerical simulation were used to analyze the influences of degree of hardness, softness and convexity of casing convex point on the rubbing response of rotor. Results showed that when the material of the casing convex point was comparatively hard, quasi-periodic motion of rotor could appear at lower speed. For a sharp convex point, the system response turned out to generate phenomenons of nonlinearities including periodic and quasi-periodic motions. When the clearance between rotor and stator was smaller, nonlinear vibration of the system would come into being in a region of high rotating speed.
Multiaxial fatigue life prediction based on non-proportionalityof strain path
ZHONG Bo, WANG Yan-rong, WEI Da-sheng, YANG Long
2016, 31(2): 317-322. doi: 10.13224/j.cnki.jasp.2016.02.008
Abstract PDF(745KB) icon1429 icon518
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A non-proportionality description was proposed based on the analysis of several commonly used non-proportionalities in multiaxial fatigue. Furthermore, a new multiaxial low cycle fatigue life prediction model was developed by combining the newly defined non-proportionality with the strain parameter of the design criterion for non-proportional fatigue in the American Society of Mechanical Engineers(ASME) code case, which was considered as the basic damage parameter. On the basis of analytical study, conclusions can be drawn as follow:(1) the defined non-proportionality can accommodate arbitrary paths with the given contour under variable amplitude and non-periodic loadings;(2) compared with two commonly used models, the predicted multiaxial fatigue lives of 304 stainless steel under 14 strain paths using the proposed model agree better with the experimental results, which are almost within two-time scatter band of the test results.
Analysis and optimization of helicopter main gearbox housing structural vibration and noise
ZHANG Lin, LI Shu, ZHANG Tao
2016, 31(2): 323-329. doi: 10.13224/j.cnki.jasp.2016.02.009
Abstract PDF(870KB) icon1471 icon546
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Structural dynamic performance analysis based on frequency response and modal contribution amount was presented about the problem of vibration and noise of helicopter main gearbox housing. The mode contributing most to the structural frequency response was found based on structural vibration performance. A method of analyzing panel acoustic power contribution amount of helicopter gearbox housing was presented based on combination of finite element method and indirect boundary element method. Acoustic radiation of the housing was simulated. The panel contributing most to the structural acoustic power under corresponding frequency was found. The panel mentioned above was the optimization area; stiffeners were reasonably arranged on the panel according to the optimization output. Result shows that,the maximum velocity frequency response has decreased 36%, vibration of the housing is attenuated, peak value of acoustic power level has decreased 5dB, and noise of the housing is reduced,which provides a feasible method to reduce noise and vibration for helicopter main gearbox housing.
Optimization reliability test design modeling based on information fusion
ZHANG An-yang, LIU Qi
2016, 31(2): 330-336. doi: 10.13224/j.cnki.jasp.2016.02.010
Abstract PDF(704KB) icon1259 icon496
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The current lack of reliability test design was analyzed by considering two types of risk(producer's risk and consumer's risk), and the optimization reliability test design modeling based on information fusion (ORTIF) was constructed. Also, the requirements and constraint conditions of reliability test design were analyzed, the information fusion technology between subsystems and systems was presented on the basis that the prior distributions were Beta distribution. According to posteriori risk criteria, the definition of producer's risk and consumer's risk were given. The solution steps of optimum test plan were given by Matlab software. At last, an example of liquid rocket engine was given. The optimum test plan (9,5,10,6,1) and its cost of 3326.9 were obtained respectively, and it was also concluded that the weight plan has a great influence on the optimum test plan.
Numerical analysis on effect of cooling air pocket area on performance of air-cooled fuel injector
LIU You-hong, WANG Xiao-bo
2016, 31(2): 337-344. doi: 10.13224/j.cnki.jasp.2016.02.011
Abstract PDF(906KB) icon1272 icon511
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Based on an air-cooled fuel injector in an afterburner of turbofan engine,geometric models cooling air pocket areas with different were obtained by changing the the upper bottom length of trapezoidal section cooling air pocket,but with the constant down bottom and height.Considering the effect of the external flow field on the internal flow and heat transfer characteristics of air-cooled fuel injector comprehensively, its conjugate heat transfer three-dimensional numerical simulation was conducted on the cruise flying state, so as to get an effect laws of different cooling air pocket areas on the entraining rate of air-cooled fuel injector,the mass flow rate of cooling air nozzle, the average cooling effectiveness and the maximum wall temperature. Results shows that, the entraining rate increases linearly with the increasing of cooling air pocket area; the mass flow rate of cooling air nozzle around the fuel nozzle convex platform changes by conic rule along the air-cooled fuel injector axis, firstly increases and then decreases; the mass flow rate tends to be uniform with increasing of cooling air pocket area; the fuel injector's and insulated jacket's average cooling effectiveness increases linearly and the maximum wall temperature decreases with the increasing of cooling air pocket area; inhibiting effectively the backflow of the hot gas into the insulated jacket is the key to avoid a partial high wall temperature.
Aero-engine certification method and safety margin of “drop-in” fuel
YANG Xiao-yi, DING Shui-ting
2016, 31(2): 345-349. doi: 10.13224/j.cnki.jasp.2016.02.012
Abstract PDF(681KB) icon1360 icon514
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A convenient method ensured the safety of airworthiness was developed to research the safety performance of aviation alternative fuel in case of lacking enough flight data of aviation alternative fuel,and it is almost impossible to evaluate the safety performance by limited engines and flight experiments. On the base of the fuel as one of the engine replacement parts, the safety of alternative fuels can be complied with compliance verification method, including to extract a fuel-independent safety criterion from the history experience and to compare the aero-engine safety of alternative fuels by similar analogy. The critical parameters with the characteristic parametric numerical description have been extracted on five levels: fuel specification level, fuel system level, component level, engine level and aircraft level. The work margin of critical parameters obtained from alternative fuel are analogized with the safety margin of critical parameters based on kerosene flight experience, and accordingly the results can be analyzed and identified the safety of aero-engine in alternative fuel. This certification process help to achieve on the safety of alternative fuel and the cost on the refining fuel required as same as kerosene. Accordingly, the safety margin can bridge the gap from kerosene flight experiences to aviation alternative fuel safety certification. The optimization methodologies for the production and distribution of alternative fuel will be established based on the safety sensitivity analysis of aero-engine and a fuel-independent safety standard.
Impact of atmospheric and ground infrared radiation on infrared stealth effect of long-wave band low emissivity of high-flying aircraft
HUANG Wei, JI Hong-hu, LU Hao-hao
2016, 31(2): 350-359. doi: 10.13224/j.cnki.jasp.2016.02.013
Abstract PDF(1021KB) icon1202 icon519
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The impact of atmospheric and ground infrared radiation reflected by skin on the infrared stealth effect of low emissivity material of high-flying aircraft was computed and analyzed. The recovery temperature was applied to calculate the skin temperature, and the infrared radiation was computed by the reverse Monte Carlo method. Both summer and winter, the two typical climate conditions were considered in the computation. And both subsonic and supersonic cruise, the two typical flight conditions were also considered in the computation. Results show that,the reduction efficiency of low emissivity material on the aircraft infrared radiation is reduced 1.5%-6%;the detection distance of the detector is increased by 20%-70% considering the reflected infrared radiation of background infrared radiation; the infrared radiation of low-speed aircraft is more susceptible to the background infrared radiation, and the effect of summer is more obvious than winter; if reducing the emissivity of the upper surface of a low-speed aircraft, the total surface of a high-speed aircraft can get a better infrared stealth effect.
Heat transfer characteristics in U-shaped rib-roughened channel at high rotation numbers
ZHANG Hong, TIAN Shu-qing, DENG Hong-wu, LI Yang
2016, 31(2): 360-368. doi: 10.13224/j.cnki.jasp.2016.02.014
Abstract PDF(1201KB) icon1189 icon530
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To match the rotor blade of real engine operating condition, the Reynolds and rotation number range of current experiment were expanded from 10000 to 70000 and 0 to 2.08 by increasing the pressure of the air in the U-shaped channel to 500kPa. Experiments were conducted to investigate the heat transfer characteristics in a square U-shaped channel with inclined 45 deg ribs. Results indicated that,in the first passage of the U-shaped channel, heat transfer coefficient of leading wall firstly decreased with the increase of the rotation number, then increased with the rotation number after reaching a critical value; in the second passage of the U-shaped channel, the difference of heat transfer coefficient between leading and trailing walls was not obvious at low rotation number, but kept increasing with the rotation number to a higher level; the heat transfer of leading wall behaved better than trailing wall, which was totally different from that of a smooth channel.
Thermodynamic cycle performance of detonation gas turbine with variable specific heat capacity
LI Xiao-feng, XIAO Jun-feng, WANG Wei, WANG Feng, WEI Shi-rang, ZHENG Long-xi
2016, 31(2): 369-376. doi: 10.13224/j.cnki.jasp.2016.02.015
Abstract PDF(882KB) icon1356 icon499
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In order to analyze the thermodynamic cycle performance of detonation gas turbine with variable specific heat capacity, the thermodynamic cycle model of detonation gas turbine was established by considering the specific heat capacity varying with the composition and temperature of the working fluid, as well as the efficiency of the compressor, combustor, turbine and other components. Under different comparison conditions, the thermodynamic cycle performances of detonation cycle of gas turbine (DCGT), Brayton cycle and Humphrey cycle gas turbine were analyzed by using variable specific heat capacity method. The results show that the performance of DCGT is better than that of Brayton cycle. When the turbine inlet temperature is 1620K and the pressure ratio is 16.5, the thermal efficiency of DCGT is increased by 28.8% compared with Brayton cycle. When the dimensionless absorbed heat is 4.25 and the pressure ratio is 16.5, the thermal efficiency of DCGT is 30.7% higher than Brayton cycle.
Self-ignition in supersonic flow induced by oblique shock wave
XI Wen-xiong, SUN Ming-bo, LI Qing
2016, 31(2): 377-382. doi: 10.13224/j.cnki.jasp.2016.02.016
Abstract PDF(881KB) icon1249 icon493
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Hydrogen and ethylene self-ignition induced by oblique shock wave were investigated experimentally with incoming Mach number of 2.5. The process of initial flame kernel generation and evolvement was observed with schlieren photography and high speed camera system. The effects of total incoming temperature, fuel injection conditions, cavity length and oblique shock wave intensity on the process of self-ignition and self-ignition boundary were studied experimentally. Results reveal that the performance of self-ignition can be improved by the enhanced effect of incident oblique shock wave on local flow-field. The low speed circulation zone created in cavity is beneficial to the upstream spreading of initial flame kernel, and acts as a function of flame-holding for preventing the blow-away of formed flame caused by flow oscillation. Self-ignition can be extended by increasing the injection pressure, cavity length and total incoming temperature.
Tip leakage flow and heat transfer characteristics with effect of trailing edge cutback on squealer tip
CHENG Feng-na, CHANG Hai-ping, ZHANG Jing-yang, TIAN Xing-jiang, DU Zhi-neng
2016, 31(2): 383-390. doi: 10.13224/j.cnki.jasp.2016.02.017
Abstract PDF(985KB) icon1120 icon478
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Comparative study was carried out to investigate the leakage flow field, leakage mass flow rate, leakage flow loss and surface heat transfer coefficient of trailing edge cutback on squealer tips by numerical simulations. Research results show that the suction side trailing edge cutback on squealer tips can change the leakage flow path near the cutback area, and suppress the mixing of the leakage flow and the main stream effectively compared with the cavity tip. Both suction and pressure sides trailing edge cutback on squealer tips can increase the leakage mass flow rate. Pressure side trailing edge cutback on squealer tips can increase the tip clearance leakage flow loss with the increase of cutback length. Suction side trailing edge cutback on squealer tips within the studied range can decrease the tip leakage flow loss, but there is an optimum cutback length. Both pressure and suction sides trailing edge cutback on squealer tips can increase the tip surface heat transfer coefficient slightly.
Study on surrogate model of endothermic hydrocarbon fuel RP-3
CHENG Ze-yuan, ZHU Jian-qin, JIN Zhao
2016, 31(2): 391-398. doi: 10.13224/j.cnki.jasp.2016.02.018
Abstract PDF(947KB) icon1431 icon486
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Numerical computations of density, viscosity, thermal conductivity and specific heat of five kinds of surrogate models for endothermic hydrocarbon fuel RP-3 by extended corresponding state law were conducted. In the computation, the temperature and pressure ranged from 300K to 800K and from 3MPa to 6MPa, respectively. Results indicated that all surrogate models could qualitatively reproduce sharp variation of physical property of RP-3 in the vicinity of pseudo-critical temperature; a three-species surrogate model consisting of mole of 53% n-undecane, 18% n-butylcyclohexane, 29% 1,3,5-trimethyl-benzene performed best among five physical surrogate models in predicting physical property of RP-3. The relative errors of this surrogate model for density were less than 0.08 at the temperature from 300K to 700K. Pseudo-critical temperature increased with growing relative molecular mass of surrogate models, showing that there was no obvious relationship between thermal properties under pseudo-critical temperature and relative molecular mass of surrogate models.
Effects of rotor blade icing on helicopter flight performance
XU Yu-mao, LÜ Shao-jie, CAO Yi-hua, CHEN-Rui
2016, 31(2): 399-404. doi: 10.13224/j.cnki.jasp.2016.02.019
Abstract PDF(823KB) icon1376 icon491
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Based on the rotor icing tunnel derivation formula, and combining with the rotor icing model and discrete rotor aerodynamics model, the lift force, drag force and flapping incremental coefficient of each rotor disk area were calculated, the UH-60A helicopter nonlinear flight dynamics model in icing condition was established.Combined with the engine power data, the effect of icing-related variables on the maximum level flight speed, maximum vertical climb rate and the maximum climb rate were studied in detail by changing the icing conditions. Results show that, when the atmospheric temperature is between 0℃ and -10℃, lowering atmospheric temperature can severely degrade the flight performance; liquid water content has a certain influence on the selected performance indexes; median volumetric diameter has little effect on the maximum level flight speed, and the impact on climb performance can be neglected; the flight performance indexes linearly decline with icing time.
Simulation test of a powder starting system of a missile engine
ZHU Rong-chuan, LIU Zhi-gang, GU Yang, DAI Guo-zhi, HE Yuan
2016, 31(2): 405-412. doi: 10.13224/j.cnki.jasp.2016.02.020
Abstract PDF(1378KB) icon1179 icon489
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For the requirements of a missile engine power starting test object, the technique index of the simulation test rid was decided by static pyrotechnic test data. Both the high pressure cold-air blowing test and the real powder hot-air blowing test were accomplished to get the starting characteristics of the simulator rotor. The test results showed that: the relational expression could be fitted by the air flux and rotation speed under different pressures measured in the static pyrotechnic test and high pressure cold-air blowing test. With the relational expression, the possible maximum rotation speed of the gas generator rotor using hot air with specific powder quantity could be forecasted. At last, the maximum rotation speed was obtained in the hot-air blowing test using 0.8kg real powder.Compared with the maximum rotation speed obtained in the cold-air blowing test under reduced pressure, the difference was only 116r/min. This further proved the validity and accuracy of the forecasting method. It will decrease or cancel the blowing tests of the simulator rotor using powder of different quantities and reduce the test safety risk. The experimental research will lay a foundation for the application on real engine.
Power characteristics of the compound helicopter in transition flight mode
CAO Fei, CHEN Ming, TIAN Li, DENG Yang-ping
2016, 31(2): 413-420. doi: 10.13224/j.cnki.jasp.2016.02.021
Abstract PDF(760KB) icon1271 icon477
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To study the power and transmission system's power division of compound helicopter in its particular flight style, a comprehensive performance calculation model that consists of the mathematical model combining the aerodynamics parts and mechanical drive system parts was established. By limiting the flight conditions, the compound helicopter's transition flight border was established. After calculating the power of different routes in the transition flight border, what impact the aerodynamics parts and mechanical drive system parts had on the compound helicopter during the transition flight was analyzed. By a ground test simulating power division in that flight style, the date validation for mathematical model was made. Although there is error of 6% between the computing result and the experimental result, the accuracy has been improved 4% compared with the traditional calculation method. According to this method, it's possible to establish a more effective compound helicopter performance calculation method.
CFD analyses of aerodynamic characteristics of tilt-rotor under typical flight conditions
LI Peng, ZHAO Qi-jun
2016, 31(2): 421-431. doi: 10.13224/j.cnki.jasp.2016.02.022
Abstract PDF(1276KB) icon1420 icon499
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Considering three flights (hover/cruise/transitional mode) of tilt-rotor, numerical simulations on the aerodynamic characteristics of tilt-rotor under different conditions were conducted respectively. Firstly, a multi-layer moving embedded grid method was established. Secondly, the unsteady RANS ( Reynolds averaged Navier-Stokes) equations were taken to simulate the unsteady characteristics of the flowfield around tilt-rotor. In order to improve the computational efficiency, the implicit LU-SGS (lower upper symmetric Gauss Seidel) method and the SPMD (single program multiple data) mode of parallel computing were employed. Finally, based on the grid method generation and flow solver, the aerodynamic characteristics of tilt-rotor under different flight conditions were numerically analysed, proving that the method presented is effective to simulate the aerodynamic characteristics of tilt-rotor. Result shows that, in hover mode, the downwash of the tilt-rotor is more obvious than the helicopter rotor. The aerodynamic interference between the tilt-rotor is apparent when the distance of the tilt-rotor shafts is 2.5R in cruise mode. In the conversion mode, the thrust decreases rapidly before the 45° tilting angle, and the thrust distribution on surface of tilt-rotor blade is similar to the helicopter rotor.
Effects of synthetic jet frequency on the separated flow in a diffusing S-duct
HE Peng, DONG Jin-zhong
2016, 31(2): 432-442. doi: 10.13224/j.cnki.jasp.2016.02.023
Abstract PDF(1045KB) icon949 icon455
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Numerical simulations were carried out to investigate the effects of synthetic jet actuation frequency on the separated flow in a diffusing S-duct. The Reynolds number based on the entrance height was 9.78×105. At first, the numerical model was validated with experimental data, and then, the interaction between the separated flow and the synthetic jets at different frequencies was discussed. The results demonstrate that the control effect is significantly dependent on the momentum mixing enhancement between inside of the separated boundary layer and the outer flow. There exists a narrow range of actuation frequency, in which effective separation control can be achieved using synthetic jets. A dimensionless frequency F+=1.0 is identified as the optimal frequency, with a momentum coefficient of 1.62×10-3, the separation area is reduced about 46%, and the aerodynamic performance of the S-duct is also greatly improved compared to uncontrolled case. Further analysis reveals that the choice of actuation frequency is mainly determined by the momentum flux produced by a single ejection and the spacing between adjacent ejections, the optimal frequency case can be understood as a balance between the two factors. In addition, it is found that the synthetic jets can also suppress the secondary flows while decreasing the separation.
Convergence analysis of hypersonic turbulent flow calculation at compression corner
XIA Chen-chao, ZHAO Wen-wen, CHEN Li-hua, CHEN Wei-fang
2016, 31(2): 443-450. doi: 10.13224/j.cnki.jasp.2016.02.024
Abstract PDF(830KB) icon1313 icon478
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The hypersonic compression corner flow was simulated by a fully coupled implicit method based on the shear stress transport (SST) turbulence model. Influence of seven factors including schemes, limiter functions and turbulence time steps, etc, on the robustness and convergence of calculation were evaluated. Results show that schemes and limiter functions have great influence on the convergence characteristic, and those with higher dissipation show better convergence characteristic of schemes and limiter functions. The increase of turbulent time step has little effect on convergence. The proper decrease of lower bound of turbulent variables can accelerate the convergence of turbulence equations substantially. Increase of Courant-Friedrichs-Lewy (CFL) number and inner iteration number of the lower-upper symmetric Gauss-Seidel (LU-SGS) method can accelerate the convergence greatly, while there are optimal values for different cases, the acceleration effect is not obvious if exceeding the optimal values.
Consistent capacity research on endothermichydrocarbon fuels and superalloy
ZHANG Zhong-li, LI Bin, ZHANG Meng-zheng, ZHOU Li-xin
2016, 31(2): 451-458. doi: 10.13224/j.cnki.jasp.2016.02.025
Abstract PDF(848KB) icon1227 icon447
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The course of consistent capacity research was demonstrated from endothermic hydrocarbon fuels and nickel-base-alloy, and the co-heating device was designed for the fuels and alloy. The mechanical capacity and metallographic diagram were gained, whenever the passivated test-slices of GH625 and GH3128 were put under wall temperature about 500-850℃, pressure about 3.5MPa, fuel temperature about 450-500℃, and velocity about 1-5m/s fuels. The experiment results showed that, under the fuel temperature about 500℃ and test-slice temperature about 850℃, the coking capacity of GH3128 was less than GH625, and the plastic stress declined about 40% for GH3128 and 60% for GH625. After the test-slice of alloy was passivated, the coking capacity was obviously cut down.
Effect of inlet internal contraction ratio on performance of solid fuel scramjet
LI Biao, WEI Zhi-jun, CHI Hong-wei, WANG Ning-fei
2016, 31(2): 459-466. doi: 10.13224/j.cnki.jasp.2016.02.026
Abstract PDF(715KB) icon1193 icon482
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To investigate the interaction between inlet and combustor of solid fuel scramjet, various engine components were designed preliminarily at a design point of Mach number of 6 and altitude of 25km. A series of engine models with different inlet internal contraction ratios were simulated numerically. Results show that when the inlet internal contraction ratio increases and combustor structure kept unchanged, the thrust and specific impulse of engine decrease rapidly and increase slightly; with the same area expansion ratio at combustor inlet, the overall performance of engine is improved as inlet internal contraction ratio increases. On the premise of inlet starting and flame holding, the inlet internal contraction ratio should be as large as possible, while the area expansion ratio at combustor inlet should be as small as possible in the engine design.
Application of SVM in stability of gas pressure reducing regulator
SUN Shi-yuan, WANG Yong-jun, CHEN Yang, WANG Bao-shan, CHEN Jing-lu
2016, 31(2): 467-476. doi: 10.13224/j.cnki.jasp.2016.02.027
Abstract PDF(1139KB) icon1478 icon475
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Support vector machine (SVM) was used to study the stability problem of high pressure unloading diaphragm pressure reducing regulator in the turbine gas seal pressure reducing test system. The research mainly focused on multi-structural parameters variation, which was difficult to solve by the classical methods. By comparing SVM and back propagation (BP) neural network model in the scarce and incomplete data set, several conclusions were proposed: the prediction models of SVM can get 25.5% less error in average and are superior to BP neural network model in the situation of multi-structural parameters variation; the generalization of SVM is also better than BP's in sparse samples space; suggestions of adjusting parameters are given for achieving good stability, and better decision-making is provided by SVM models in design of pressure reducing regulator,with double parameter combinations and tri-parameter combinations.
FPGA-based autonomous over-speed protection system for aero-engine
JIANG Wen-liang, LU Qian-li, YU Zhen, ZHU Yin-yu, HUANG Jin-quan
2016, 31(2): 477-483. doi: 10.13224/j.cnki.jasp.2016.02.028
Abstract PDF(784KB) icon1359 icon460
Abstract:
To prevent the aero-engine from over-speed, an autonomous over-speed protection system based on field-programmable gate array(FPGA) was proposed. The protection strategy, over-speed realization and fault detection of system were presented. A double dual-redundancy protection structure was employed to ensure system stability. Over-speed protection was enhanced by linear classifier and weighted voting mechanism with sliding window. A three-layered built-in-test (BIT) technique was developed to monitor the fail-silent process and meet the airworthiness requirement. The protection system was testified based on extensive experimental results through hardware-in-the-loop tests, demonstrating that the proposed protection system is able to determine the over-speed with high accuracy and reliability, and lock the protection status against the consecutive over-speed effectively to prevent the structural failure of the aero-engine. The system has been successfully applied into a certain type of full authority digital engine control (FADEC) system.
Fault diagnosis for actuators of aero-engine fuel system based on NN-ELM
JIANG Jie, LI Qiu-hong, ZHANG Gao-qian, LI Ye-bo
2016, 31(2): 484-492. doi: 10.13224/j.cnki.jasp.2016.02.029
Abstract PDF(912KB) icon1409 icon436
Abstract:
A single fault diagnosis and location method of aero-engine actuator and its sensor was proposed. Fault of actuator was diagnosed according to the actuator model and located according to the inverse engine model. The actuator model was built based on offline training BP(back propagation) neural network (NN). The network parameters were trained according to the test data of a semi-physical simulation test bed. The inverse engine model based on offline and online extreme learning machine (ELM) had original diagnosis ability and adaptability during operation. The training samples were selected using the threshold discrimination, which can reduce the online training time and improve the real-time property of inverse model during the online training process. Design and simulation results of a certain engine fuel system actuator show that,the proposed system can diagnose and locate the single faults of engine actuator or its sensor accurately in steady state, dynamic state and degradation state. The real-time property can be satisfied.
Vortex generators control flat boundary layer separation of large eddy simulation
HU Hao, LI Xin-kai, DAI Li-ping, WANG Xiao-dong, KANG Shun
2016, 31(2): 493-502. doi: 10.13224/j.cnki.jasp.2016.02.030
Abstract PDF(953KB) icon1236 icon450
Abstract:
In order to study the effect of spacing λ of vortex generators(VGs) on the control boundary layer separation, 4 kinds of vortex generators spacing were selected, and λ/H(H is the height of vortex generators) respectively were 5, 7, 9, 11. The boundary layer separation flow of adverse pressure gradient and VGs control flow separation were simulated by large eddy simulation(LES) method. The evolution of the large scale coherent structure in turbulent flow field were analyzed with and without VGs control, and the influence of VGs spacing on the flow separation control effect were investigated from vortex spacing, fluid kinetic energy in the boundary layer, loss of pressure difference, etc. The research results show that when λ/H is 5, the spacing of VGs is too small, so that the spanwise development of vortex are suppressed, when λ/H are 9, 11, the spacing of VGs is too large lead to the fluid kinetic energy in the boundary layer is too low, when the spacing of VGs is λ/H is 7, the effect of flow control is better, then the pressure loss of calculation domain is minimum, compared with no VGs control, pressure loss is reduced by 30.95%.
Coupling optimization design for aspirated compressor airfoil with low Reynolds number in high altitude
LI Jun, LIU Bo, YANG Xiao-dong, LU Xiao-feng
2016, 31(2): 503-512. doi: 10.13224/j.cnki.jasp.2016.02.031
Abstract PDF(945KB) icon1256 icon454
Abstract:
Aim at researching the aerodynamic design characteristics of the aspirated airfoil with low Reynolds number in high altitude, artificial bee colony algorithm(ABC) was used to optimize the aspirated airfoil in the condition of low Reynolds number, and this design method coupled the airfoil and aspirated scheme in the process of optimization design. And the necessity of the coupling optimized design was demonstrated.Research results show that: the performance of the aspirated airfoil designed in the condition of the ground would decrease significantly in the condition of low Reynolds number, and the coupling optimized design in the condition of low Reynolds number is necessary.The coupling optimized design can reduce the total pressure loss by 32%, and increase the static pressure ratio by 0.01 in the condition of low Reynolds number.And the performance of the aspirated airfoil could also be promoted in the condition of the ground.The design is optimum by improving the load in the forepart of the aspirated airfoil appropriately, and controlling the laminar bubble by aspiration.And the optimal aspirated location is in the center of the laminar bubble.

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