2021 Vol. 36, No. 12

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Recognition of gearbox operation fault state based on CWT-CNN
LIANG Ruijun, RAN Wenfeng, YU Chuanliang, CHEN Weifang, NI De
2021, 36(12): 2465-2473. doi: 10.13224/j.cnki.jasp.20210450
Abstract FullText HTML PDF(4083KB) icon2965 icon274
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In view of the problem that the features extracted by the traditional fault diagnosis do not have adaptive ability and are difficult to match specific faults，a method for fault detection of gearbox based on the continuous wavelet transform （CWT） and two-dimensional convolutional neural network （CNN） was proposed.This method constructed the time-frequency diagrams to raw vibration signals through CWT，then built the CNN model using the diagrams as input，and finally formed a deep distributed fault feature expression through the multiple convolutions and pooling operations.The back propagation algorithm was used to adjust the structural parameters of each layer of the network，making the model establish an accurate mapping from the signal characteristics to the fault states.In experiments under different working conditions and fault states，the fault recognition accuracy reached 99.2%，which verified the effectiveness of the proposed method.Using this method of adaptive learning the abundant information in the signal can provide a basis for the intelligent fault diagnosis.
Flow field and damping characteristics of piston ring sealed squeeze film damper
CUI Ying, LUO Qiaodan, QIU Kai, HUNAG Yuxi
2021, 36(12): 2474-2481. doi: 10.13224/j.cnki.jasp.20210445
Abstract FullText HTML PDF(3640KB) icon592 icon165
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In order to study the flow field and damping characteristics of squeeze film damper sealed at both ends，a three-dimensional unsteady flow field numerical simulation model of squeeze film damper with piston ring seal was established.The circumferential oil film pressure distribution at different times was calculated based on the Mixture multiphase flow model and Schnerr-Sauer cavitation model in Fluent software，and compared with the experimental data in literature.The results showed that both were in good agreement.The average equivalent damping coefficient derived from the dynamic oil film force had only a deviation of 0.6% compared with the results identified by the impedance method，which verified the effectiveness of the numerical model.Further numerical calculations demonstrated that increasing the whirl amplitude，whirl frequency and the width of piston ring gap can aggravate the cavitation phenomenon in the flow field of the squeeze film damper and reduce the equivalent damping coefficient.
Low cycle fatigue behavior and life prediction model of TiAl superalloy
LI Wei, JIANG Kanghe, MA Li, ZENG Wu, YANG Junjie
2021, 36(12): 2482-2489. doi: 10.13224/j.cnki.jasp.20210440
Abstract FullText HTML PDF(3763KB) icon676 icon186
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Axial strain-controlled low cycle fatigue （LCF） tests were carried out on the TiAl superalloy at 400 ℃ and 750 ℃ to obtain the cyclic behavior and LCF lifetime.The superalloy exhibited stable cyclic characteristics，i.e.no obvious cyclic softening or cyclic hardening during test.The cyclic stress-strain relationship was well described by the Ramberg-Osgood equation.LCF lives at different temperatures had a log-linear relationship with the total strain ranges.Fracture morphology revealed that the TiAl superalloy presented pronounced ductile fracture and significant oxidation at 750 ℃，while the brittle fracture of the material was obvious at 400 ℃.Meanwhile，translamellar fracture was dominant for the lamellar microstructure at both temperature，and the percentage of the interlamellar fracture decreased with the strain amplitude.It was noteworthy that oxidation was significantly accelerated at 750 ℃.Compared to the Manson-Coffin model，although the Cruse-Meyer model had simpler mathematical form and fewer material constants，it was not accurate enough to predict the life of the tenon part of turbine blades with lower temperature but heavy centrifugal load.Hence，the model was not suitable to be applied to TiAl turbine blade directly.
Analysis on analytical modelling and damping characteristics of bolted joint structure with spigot
YU Pingchao, ZHAO Zhimei, HOU Li, CHEN Guo
2021, 36(12): 2490-2502. doi: 10.13224/j.cnki.jasp.20210297
Abstract FullText HTML PDF(5890KB) icon410 icon142
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For the bolted joint with spigot，a nonlinear model for the single region of bolted joint under axial loads was built.Based on this model，the nonlinear analytical model was further proposed to describe the behavior of joint under bending moment.By performing a comparison study with the finite contact element model，the accuracy of the analytical model was validated，meanwhile，the nonlinear stiffness and damping characteristics of the joint were highlighted.Finally，the influence law of key parameters on joints' damping characteristics was investigated.The results showed that the ability of damping dissipation of bolted joint firstly increased and then decreased with the increase of bending moment amplitude and friction coefficient，while the ability of damping dissipation increased for the increasing interference fit of spigot and flange length.More importantly，flange length can not only affect the damping characteristics，but also decrease the equivalent stiffness of bolted joint significantly.
Influence factors of nonlinear stiffness of bolted flange connection structure under different loads
WANG Kaiping, YAN Ming, SUN Ziqiang, SU Donghai, HUI Anmin, LIU Haichao
2021, 36(12): 2503-2514. doi: 10.13224/j.cnki.jasp.20200539
Abstract FullText HTML PDF(5449KB) icon699 icon168
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In order to study the influence of various factors on the nonlinear stiffness of bolted flange connection structure，a fine finite element model of screw connection structure with rising angle was established，the full hexahedron mesh generation was carried out，and the validity of the model was verified.The simulation analysis under tension，bending and torsion load was carried out respectively.The results showed that the larger initial pre-tightening force indicated the greater bending and torsional stiffness of the connection structure，and the initial pre-tightening force had no influence on the tensile stiffness.Under the tensile load，the initial preload increased the critical resistance of the separation of the two flanges.Under the bending load，the greater initial preload indicated the greater external bending moment triggering the opening of the two flanges，and it was more difficult for each bolt to bear the external force.Before the opening of two flanges，the initial pre-tightening force had little influence on the bending stiffness of the connection structure，but the influence was greater after the opening；the larger diameter and more number of bolts indicated the greater tensile，bending and torsional stiffness of the connection structure；the closer bolt position to the flange tube indicated the greater tensile stiffness of the connection structure.The friction coefficient between the joint surfaces had no influence on the tensile and bending stiffness of the connection structure.The greater friction coefficient between the joint surfaces indicated the greater torsional stiffness of the connection structure.The friction coefficient between the flange and flange joint surface had a greater influence on the torsional stiffness in the first section of the stiffness curve，while the friction coefficient between the bolt flange joint surface had a greater influence on the second section.
Numerical simulation of small crack growth in selective laser melting TC4
XU Yufei, HU Dianyin, MI Dong, PAN Jinchao, WANG Rongqiao
2021, 36(12): 2515-2523. doi: 10.13224/j.cnki.jasp.20210043
Abstract FullText HTML PDF(4323KB) icon425 icon151
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A numerical simulation method of small crack growth in selective laser melting （SLM） titanium alloy TC4 considering microstructure was developed.Based on the microstructure observation results of SLM TC4，the microstructure modeling was realized by Voronoi diagram and crystallographic orientation screening.The extended finite element method was used to establish the simulation method for small crack growth behavior of SLM TC4 to explore the influences of buildup direction，grain size，crystallographic orientation and other microstructure on the small crack growth rate.The buildup direction affected the crack growth resistance，and the material had better resistance to fatigue small crack growth when the buildup direction was parallel to the crack growth direction.The grain size affected the small crack growth rate，the growth rate of small crack became faster with the increase of grain size.The crystallographic orientation affected the volatility of the crack growth rate，the upper and lower bounds of small crack growth rate of materials with different crystallographic orientations were obviously different.
Influence law of blade profiling of wide-chord fan on rub-induced vibration
CHEN Dawei, XIAO Jiaguangyi, CHEN Yong
2021, 36(12): 2524-2536. doi: 10.13224/j.cnki.jasp.20210054
Abstract FullText HTML PDF(5579KB) icon394 icon91
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Based on the superposition principle of geometric features，a parameterized wide-chord fan blade model was established，and the influence of blade profiling on rub-induced vibration was also studied by rub-impact dynamics.The complex geometric shape of wide-chord fan blades may enhance the rubbing nonlinearity，so it is necessary to study the influence of blade geometry on the rub-induced vibration.The relationship between the blade profiling and geometric parameters was established in the cylindrical coordinate system，and the parameterized model of the fan blade was obtained.With the calculation of blade tip clearance simplified by cubic spline fitting，the correlation between the vibration response，coating wear and blade stress of the basic blade was investigated under eccentric rubbing conditions.The blade rubbing characteristics of different geometric features were analyzed by the degree of wear of abradable coating，realizing the rapid analysis of rubbing vibration and blade profiling.The calculation results showed that the inner flow path angle had a significant influence on the blade length and natural frequency，which adjusted the center resonance frequency；by changing the direction of minimum bending stiffness，the tip twist angle effectively reduced the rubbing resonance interval；compared with the forward-lean blade，the backward-lean blade had better rubbing stability.
Influence of precision of tangential port diameter on performance of swirl atomizer
ZHANG Ya, LIU Qian, XIE Heng
2021, 36(12): 2537-2544. doi: 10.13224/j.cnki.jasp.20200532
Abstract FullText HTML PDF(3632KB) icon383 icon115
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In order to solve the problem of large deviation between theoretical calculation and test data of discharge coefficient of swirl atomizer，a two-phase flow computational model with Fluent was taken to investigate the performance of a swirl atomizer.The influences of machining precision of tangential port diameter on performance parameters，including spray angle and discharge coefficient were simulated.The results showed that the discharge coefficient was influenced obviously by the tangential port diameter precision.The average diameters of tangential ports of 4 swirl atomizers were measured using plug gauges.Models with measured average diameters were taken to evaluate the performance of the swirl atomizers under a wide range of different pressure drops，and the result was compared with test data.The computational results agreed well with the test data，the error of spray angle was less than 1°，and the discharge coefficient difference was within 4.2%.
Thermal performance of microencapsulated phase change material slurry in treelike microchannels
MA Jie, SUN Li, LI Songlin, PENG Hao, WANG Gang, CAI Han
2021, 36(12): 2545-2554. doi: 10.13224/j.cnki.jasp.20200555
Abstract FullText HTML PDF(4020KB) icon396 icon84
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Micro-encapsulated phase change material slurry （MEPCMS） was prepared using glycol solution as cold-based solution，and its physical properties were measured.Then，the thermodynamic properties of MEPCMS in tree microchannels were experimentally studied to reveal the influence of Reynolds number and mass concentration on the thermodynamic properties of MEPCMS.The results showed that the specific heat capacity of MEPCMS increased with the increase of microcapsule mass concentration and temperature，and the viscosity of MEPCMS increased with the increase of microcapsule mass fraction and the decrease of temperature.The convective heat transfer coefficient of MEPCMS increased with Reynolds number and mass concentration.When Reynolds number was 118，the convective heat transfer coefficients of MEPCMS at 1% and 3% mass fraction increased by 3.92% and 9.04%，respectively，compared with the base solution.The friction factor of MEPCMS decreased with the increase of Reynolds number and the decrease of mass concentration，but the friction factor of MEPCMS gradually approached the base solution with the increase of Reynolds number.
Numerical investigation of high altitude aerodynamic and spray fields for multi-swirl airblast atomizer
ZHAO Qianpeng, YANG Jinhu, LIU Cunxi, LIU Fuqiang, MU Yong, HU Chunyan, XU Gang
2021, 36(12): 2555-2567. doi: 10.13224/j.cnki.jasp.20210050
Abstract FullText HTML PDF(7067KB) icon454 icon163
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In order to effectively widen the stable operating limits of multi-swirl staged combustor with prefilming airblast atomizer，the aerodynamic and spray fields of a model combustor under plateau and high-altitude conditions were studied numerically.A numerical method verified by experiments was used to acquire the high-altitude aerodynamic and spray fields of a multi-swirl staged combustor.The influences of low temperature and sub-atmospheric pressure conditions on the flow field structure and atomization quality were analyzed.The results showed that the low temperature and sub-atmospheric pressure conditions had little influence on the flow structure，scale and velocity distributions of central recirculation zone.However，the low temperature weakened the turbulent intensity in swirler outlet，and the sub-atmospheric pressure significantly reduced the tangential shear force of swirling air.Under the same pressure drop of injector，the low temperature and sub-atmospheric pressure conditions led to the decrease of air-liquid ratio and Weber number，which further led to the increase of droplet size and the axial penetration depth of droplet group.The findings from this investigation can explain the influence mechanism of altitude relight difficulty for this kind of combustor.
Effects of swirl cup structure on fuel atomization particle size of fuel
CHEN Sumin, JIANG Lei, WANG Tong, HU Hongbin, WANG Bohan, JIANG Xiangyu
2021, 36(12): 2568-2577. doi: 10.13224/j.cnki.jasp.20200547
Abstract FullText HTML PDF(4124KB) icon377 icon94
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In order to deeply study the effects of inlet parameters，swirl cup structures and axial coordination of fuel nozzle and Venturi of swirl cup on the atomization particle size of aviation kerosene，the LSA （laser size analyzer）-Ⅲ was used to measure the Sauter mean diameter （SMD） at 35 mm downstream the outlet of the co-rotating axial swirl cup under ambient temperature and pressure.The results showed that with the increase of the total pressure loss coefficient of the swirl cup，the SMD of fuel decreased，while the decreasing trend slowed down.The SMD was small near the case of 35° vane installation angle.The inner and outer swirling intensity should be matched with each other，which together could affect the fuel pre-filming and fuel sheet breakup.The Venturi throat diameter affected the inner swirling intensity and the quality of film formation.While the ratio between the Venturi throat diameter and Venturi length was within the range of 1.04-1.13，the SMD was small.The spray diffusion was restricted by the sleeve divergence section.Either large or small divergence angle may lead to an increase in fuel SMD.The position of fuel nozzle and the Venturi affected the quality of liquid film breaking.
Ground performance analysis of aircraft fuel tank cooling inerting system
LIU Guannan, WANG Liqun, WANG Hongming, HUANG Long, CHEN Guanghao, FENG Shiyu
2021, 36(12): 2578-2585. doi: 10.13224/j.cnki.jasp.20200534
Abstract FullText HTML PDF(3539KB) icon508 icon69
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The working process of cooling inerting system was designed and the mathematical model of cooling inerting under ground state was established.Moreover，the relationship between the volume concentration of fuel vapor，the temperature of fuel and gas phase space and the cooling capacity with time was solved by Modelica software.In addition，the influence of several key parameters on the inerting effect was studied.The results showed that with the increase of pumping flow and the decrease of evaporation temperature，the gas phase space fuel vapor volume concentration became lower，the gas phase space temperature declined，the cooling inerting time was shorter，and the inerting effect became better.With the enlargement of internal heat source，it's more difficult to achieve cooling inerting.Although the internal heat source has a bad effect on cooling inerting，cooling inerting is a viable alternative to tank inerting.
Method for calculating machining parameters of spiral bevel and hypoid gears generated by completing method
ZHANG Yu, YAN Hongzhi, WANG Zhiyong, ZENG Tao
2021, 36(12): 2586-2595. doi: 10.13224/j.cnki.jasp.20210048
Abstract FullText HTML PDF(3529KB) icon613 icon109
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The setting method of three reference points was proposed by analyzing the structure and cutting motion of the spiral bevel and hypoid gear cutter head.Taking the spiral bevel and hypoid gears with the gear using the generating method and the pinion using the duplex helical method as the research object，a simplified calculation method of the processing parameters for the gear of completing method was proposed.The general meshing rule of spiral bevel and hypoid gears was summarized，an optimization model for the gear cutting control of the pinion was established by combining with the reference points setting method and using the flexible motion control characteristics of the Free-Form machine tool，and a set of optimal machining parameters were obtained. A design software was developed based on the above calculation method，and then based on the domestically-made computer numerical control bevel gear processing equipment，a networked closed-loop manufacturing was carried out with a pair of hypoid gears as an example.The test results showed that the transmission error amplitude was 13.2″，the contact area of the two tooth surfaces was located in the middle of the tooth surface at an inner opposite angle，which verified the correctness of this method，and effectively solved the industry problem of difficulty in synchronous adjustment of the double-sided contact characteristics when the spiral bevel and hypoid gear was processed by the completing method.
Design and test for ball bearings under high-speed and frequent start-stop
LI Hongliang, HAO Daqing, ZHENG Yanwei, CHEN Zhijun, WEI Xiaobo
2021, 36(12): 2596-2605. doi: 10.13224/j.cnki.jasp.20210330
Abstract FullText HTML PDF(4932KB) icon528 icon113
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To solve the bearings failure of turbine starters under the conditions of high-speed and frequent start-stop，the structure parameters design and material selection for turbine starters were carried out in combination with the design criteria of bearings.Based on the dynamics theory of bearings，the dynamic model was established and simulated.The dynamic behaviour for bearings of high speed，frequent start-stop conditions was investigated.The bearing test was carried out on the self-developed testing machine.During the test，the bearing temperature rose and vibration acceleration value were monitored.In case of bearing frequent start-stop and the maximum speed reaching 120 000 r/min，the test bearing temperature was lower than 130 ℃，and the vibration acceleration was lower than 3.0g.After test，the bearing was not abnormal，verifying that the bearing design and material selection were reasonable.Through optimized design and test verification，the bearing speed could be raised to 120 000 r/min，the starting time only needs 60 s，and the stopping time only needs 40 s，and the bearing can complete more than 3 000 continuous frequent start-stop.
Structural optimization and reliability analysis of hybrid dynamic pressure gas bearings
ZANG Tengfei, JIA Chenhui, ZHANG Luyao, SHI Dawei
2021, 36(12): 2606-2620. doi: 10.13224/j.cnki.jasp.20200563
Abstract FullText HTML PDF(7224KB) icon429 icon117
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By combining radial and thrust spiral groove dynamic pressure gas bearing，the lubrication analysis model of hybrid dynamic pressure gas bearing was established.The structure characteristics and lubrication mechanism of the mixed dynamic pressure gas bearing were expounded，and the dimensionless steady state Reynolds governing equation of the bearing was established.A hybrid dynamic pressure film pressure coupling calculation method was proposed，differential expression of gas film pressure was derived，boundary conditions were defined，and a numerical calculation method of gas film pressure distribution was constructed.The maximum radial bearing capacity was taken as the objective to optimize the structural parameters.Based on the optimal structural parameters，the finite element model of bearing gas film was established，and the radial stability variation law of bearing rotor system under different impact loads was analyzed using CFD，so as to study the dynamic characteristics and reliability of hybrid dynamic pressure gas bearing.The test bed of hybrid dynamic pressure gas bearing was built to verify the correctness of numerical calculation method and finite element simulation analysis.The results showed that the proposed pressure coupling calculation method can accurately calculate and analyze the steady-state gas film pressure distribution，gas film force and bearing capacity，and the finite element simulation can better simulate the dynamic flow field change，and also calculate and analyze the dynamic gas film force，dynamic characteristic coefficient and stability.The good bearing capacity and stability of the mixed gas bearing at high speed have strong impact resistance and reliability to unidirectional step force and unidirectional rectangular force.When the bearing performance and stiffness were optimized，the impact resistance and stability should be considered to improve the comprehensive performance of the hybrid gas bearing.
Stability analysis on flow field within taper tube of pneumatic measuring instrument in relation to buoy
WEI Xianjie, LONG Wei, LEI Jilin, XIN Xiaocheng, GAO Hao
2021, 36(12): 2621-2630. doi: 10.13224/j.cnki.jasp.20210040
Abstract FullText HTML PDF(5177KB) icon225 icon72
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The problem of flow around the buoy was analyzed.It was found that the tail turbulence and vortices were caused when the flow passed through the buoy from bottom to top.As the vortex moved and fell off，the turbulent flow field showed fluctuating pressure acting on both sides of the buoy in an alternating form，causing the buoy to swing from side to side and the indicator to be unstable.Further，a guide surface with length and angle was added at the tail of the buoy to reduce the influence of tail-vortex by draining the flow field at the tail.At the same time，the local air resistance in the drainage guide area was enhanced to improve the working stability of the buoy.The results showed that when the length of the guide surface increased to 2 mm，the airflow stiffness of the buoy and the inner wall of the glass pipe increased，and the deflection angle of the buoy decreased from 8° to 0.5°.When the angle of the guide surface exceeded 10°，a relatively low pressure area appeared and the deflection angle exceeded 15° due to the influence of the Cornda effect.
Simulation and sensitivity analysis of air system for the compressor test piece
ZHAO Hongjiao, XU Xianghua, LIANG Xingang
2021, 36(12): 2631-2641. doi: 10.13224/j.cnki.jasp.20210001
Abstract FullText HTML PDF(4269KB) icon286 icon139
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Based on fluid network method and mathematical models of components，the air system of engine compressor was simplified as a one-dimensional topological network composed of nodes and components.A program was developed to simulate this system for solving the flow control equations by the rotative mid-point mensuration combined with the Newton-Raphson method.The program was applied to simulation of the air system of a compressor test piece.The sensitivity analysis on the parameters of the air system of the test piece was carried out，and the main factors affecting the function of the air system were discussed.Results showed that the convergence speed and convergence region of Newton method can be increased by using the parametric differential method to solve the homotopy equation；in the compressor test piece，the flow path can be effectively separated by using the unloading chamber structure and the labyrinth with strong sealing ability，contributing to achieving the control objectives respectively.
Sound field/flow field characteristics of supersonic jet impinging on inclined plate under different pressure ratios
QI Longzhou, FENG Heying, ZHAO Kun, ZHANG Junlong, QIN Chen
2021, 36(12): 2642-2651. doi: 10.13224/j.cnki.jasp.20210042
Abstract FullText HTML PDF(4570KB) icon426 icon96
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In order to study the noise characteristics and sound source characteristics of the supersonic jet impinging on the inclined plate，the flow field and sound field of the supersonic jet under different pressure ratios were measured by high-frequency PIV （particle image velocimetry） and far-field noise.PIV measurement results can be used to observe the formation process of the shock grid and the impact of the inclined plate.The sound field measurement results can be used to capture the transition process of different tone frequencies in the free jet and the impinging jet as the pressure ratio increased.By comparing each tone mode and flow field mode one by one，the sound source characteristics of each tone mode can be distinguished.When pressure ratio was between 2.0-3.2，there were five tone modes：the tone of A mode was taken as the shear layer large-scale vortex shedding frequency，and the flow field presented a coaxial mode；the tone frequencies of the d and e modes were mainly taken as an impinging tone frequency；when the e mode appeared，the flow field transformed into a spiral mode，which was an unstable mode；when pressure ratio was more than 2.53，the tone mode was stable to a single mode B，and the tone of the B mode was taken as the screech frequency.The structure was converted back to the coaxial mode，and the screech frequency was not sensitive to the presence or absence of the inclined plate；the tone frequency of the B mode gradually decreased with the increase of the pressure ratio，and for the second harmonic frequency there was a strong sound wave radiation in the direction of the smaller amplitude of the fundamental frequency.
Simulation on dual-fuzzy energy management strategy of UAV extended range electric propulsion system
HU Chunming, LI Cheng, LIU Na, SONG Xijuan, DU Chunyuan
2021, 36(12): 2652-2662. doi: 10.13224/j.cnki.jasp.20200546
Abstract FullText HTML PDF(4835KB) icon448 icon105
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In order to improve the energy utilization efficiency of the extended-range electric propulsion system applied to unmanned aerial vehicle （UAV）s，an energy management strategy based on double-layer fuzzy control was adopted and genetic algorithms were used to optimize the control parameters，and different disturbances were set in the simulated flight conditions according to the flight dynamics theory to test the anti-flight disturbance effect of the energy management strategy.The simulation results showed that compared with the energy management strategy based on multi-point logic gate rules and PID （proportion integral differential），the dual-fuzzy energy management strategy can reduce the average fuel consumption rate of the engine by 3.4% and the overall fuel consumption by 3.8%；the battery usage was reduced by 10.6%，the average engine speed error was reduced by 77.0%，and the maximum speed fluctuations in the face of sudden wind disturbance，compound disturbance and continuous turbulence disturbance were reduced by 71.4%，72.6% and 46.7%，respectively.Compared with the control parameters before optimization，the dual-fuzzy energy management strategy optimized by genetic algorithm reduced the average engine speed error by 6.6%，and reduced the maximum speed fluctuations by 12.8%，8.3%，and 39.4%，respectively，in the face of the above-mentioned three kinds of disturbances.
Improved design of pressure reduction ratio characteristics of a nozzle afterburner regulator
WANG Fei, HUANG Yigui, YUAN Cuixia, ZHAO Zhihui, LIU Lidan
2021, 36(12): 2663-2672. doi: 10.13224/j.cnki.jasp.20210805
Abstract FullText HTML PDF(3885KB) icon309 icon87
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In order to solve the problem that the turbine drop pressure ratio deviates from the design value in the use of a nozzle afterburner regulator with an engine，the gas flow state of one-dimensional steady compressible Laval nozzle was theoretically analyzed and calculated，and the service conditions for the normal operation of Laval nozzle were analyzed according to the continuous working requirements of turbine drop pressure ratio；an improved design method for the secondary decompression Laval nozzle air pressure reducer expansion groove shape was proposed，and the engine test was conducted.The results showed that when the air pressure reducer only worked in supercritical state，and the shock wave was positioned behind the pressure measuring point location，it could ensure that relief was only associated with the position of pin plug，but had nothing to do with the inlet pressure.When the inlet pressure was low，the shock wave position was close to the pressure measuring point，which caused the deviation of the decompression ratio in the relative stable state.Increasing the throat area can make the shock position move backward and away from the pressure measuring point under the same inlet condition，which is conducive to improving the stability of the decompression ratio.Increasing the angle of the back end can make the shock position move forward，which is not conducive to the stability of the decompression ratio.
Water ingestion test technical of transport aircraft power system
ZHAO Haigang, QU Jiyun, MA Zhengsheng, FU Xiaogang, QI Xuefeng
2021, 36(12): 2673-2682. doi: 10.13224/j.cnki.jasp.20200542
Abstract FullText HTML PDF(4819KB) icon591 icon118
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On the basis of analyzing and interpreting the Chinese civil regulations transport airworthiness standards of Civil Aviation Administration of China （CAAC） and advisory circular of Federal Aviation Administration （FAA），the water ingestion test program，test pool scheme and landing speed measurement and control technology was studied and designed from two aspects of engineering test and airworthiness verification.Based on the airworthiness standard system，the procedure of transport aircraft power system water ingestion test was developed and applied in the ARJ21-700 aircraft flight test.The results showed that the designed water ingestion test procedure was reasonable and feasible，and it was able to verify power systemcompliance with standards completely when the transport aircraft passed through the water contaminated runway；the critical speed of ARJ21-700 aircraft equipped with CF34-10A engine was 166.6 km/h in aircraft taking off and slipping through the water contaminate runway；the maximum fluctuations of the rotation rate of fan and compressor，and inter turbo temperature were 5.1%，1.7% and 39 ℃.The performance of engine was better in idle state compared with maximum reverse thrust state in the aircraft landing and slipping through the water contaminated runway.So it could meet the airworthiness standard.The procedure and technology provide a direct support for the power system water ingestion test of C919，C929 and other transport aircrafts.
Aero-engine centrifugal separator performance test
CAI Yi, YANG Jiajun, MA Lei
2021, 36(12): 2683-2688. doi: 10.13224/j.cnki.jasp.20200525
Abstract FullText HTML PDF(2873KB) icon402 icon103
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Tests were performed on aero-engine centrifugal separator to gain the performance data by simulating bearing cavity oil-air mist environment.Mass and optics measurement methods were used to collect the separating efficiency，particle size distribution and pressure drop data.Test results revealed that separating efficiency increased linearly and then gently while rotation increased.Separating efficiency increased 10% while rotation increased from static state to 1 000 r/min，particles between 2.0 μm and 3.0 μm were nearly separated，and middle diameter decreased from 1.8 μm to 1.3 μm.While rotation increased up to 2 500 r/min，middle diameter kept the same and particles below 2.1 μm were kept.Air mass flow nearly had no effect on particle size distribution and separating efficiency.Pressure drop increased when air mass flow and rotation increased.

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