2022 Vol. 37, No. 5

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Rotational inertia model and dynamic response characteristics of multi-disk rotor system with interface
HONG Jie, YAN Qi, FENG Shaobao, SUN Bo, MA Yanhong
2022, 37(5): 897-908. doi: 10.13224/j.cnki.jasp.20210556
Abstract FullText HTML PDF(2318KB) icon428 icon255
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For the interface-connected multi-disk rotor system working in postcritical range，the deflection of the principal axis of inertia was used to describe the mass distribution，the time-varying characteristics of the rotating inertial load of each wheel with the speed and bending deformation were considered，and the dynamic model of the interface-connected multi-disk rotor was established.Based on the quantitative description of the mass distribution of disks under the influence of machining/assembly error and contact state of connecting structure，the dynamic response of the rotor and the dynamic load amplitude and phase of the bearing change with the speed were explored.The theoretical model and simulation results showed that in the postcritical range，the rotational inertia moment of the rotor caused the bearing dynamic load amplitude to increase with the speed continually；at high speed，the change of the contact state of the connecting structure may change the mass distribution of the multi-disk rotor，the principal axis of inertia of the rotor approached the rotation center line，the rotation inertia load on the rotor decreased，and the vibration response dropped rapidly.
Dynamic characteristics of rotor-ball bearing system with multi coupling faults
ZHONG Zhixian, MA Liyi, CAI Zhonghou, CHEN Jinhua, ZHU Changsheng
2022, 37(5): 909-923. doi: 10.13224/j.cnki.jasp.20220016
Abstract FullText HTML PDF(1598KB) icon447 icon156
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To further study the mechanism of the rotor-ball bearing system with multi coupling faults，the effects of torsional stress，shear stress，gyroscopic and moment of inertia on rotating components were fully considered，Timoshenko beam elements and disk elements were used to model the finite element of a rotor system.By assembling the dynamic model of ball bearing and fault models of unbalance，misalignment，rubbing，crack and pedestal looseness，the dynamic equations of the rotor-ball bearing system with multi coupling faults were obtained.The displacement response of the rotor-ball bearing system was obtained using Runge Kutta method with variable step length，and response was analyzed using bifurcation diagrams and poincaré maps with mass speed and time-domain waveform，axis orbits，phase diagrams and frequency spectrum at the fault areas.Fault features and dynamic characteristics of the system were studied and explored.As a result，abundant nonlinear phenomena such as periodic motion，quasi-periodic motion and complex quasi-chaotic motion were found.Additionally，characteristics of faults such as unbalance，misalignment，rubbing，crack and pedestal looseness were indicated during each nonlinear behavior.
Mechanical analysis and damage characteristics of self-lubricating joint bearings of helicopter variable-pitch tie rod ends
ZHOU Changchun, YANG Yongsheng, TAN Deqiang, YANG Xiaoqiang, HE Qiang, HU Yue
2022, 37(5): 924-933. doi: 10.13224/j.cnki.jasp.20210674
Abstract FullText HTML PDF(2711KB) icon446 icon118
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The self-lubricating joint bearings of the R44 helicopter main rotor variable-pitch tie rod ends were taken as the research objects.The rotating and swinging finite element model was established with three-dimensional modeling software Solidworks and applied to the finite element analysis software Ansys Workbench.The change characteristics of equivalent stress，displacement，contact stress and shear stress of the liner under radial sinusoidal load were analyzed and calculated，and the failure of the self-lubricating joint bearing liner of the R44 helicopter under actual service conditions was analyzed.The results showed that during the whole period，the edge of the liner was deformed due to being squeezed，and the equivalent stress and the equivalent maximum deformation of the liner appeared on the edge of the outer ring；the area with the maximum contact stress always appeared at the top and bottom of the liner，and the movement of the contact stress distribution area was consistent with the rotation direction of the inner ring； the most concentrated shear stress was in the upper left，lower left，upper right，lower right，left and right areas of the radial load application point.Due to the change of load in actual service conditions，the damage of liner was mainly caused by fatigue damage arising from contact stress in the upper part and transfer film was caused by shear stress in the lower part.
Numerical and experimental investigation on interstage pressure drop equalization of differential multi-stage brush seals
ZHAO Huan, LI Yelong, SUN Dan, MU Wei, MA Ting, HU Guangyang
2022, 37(5): 934-945. doi: 10.13224/j.cnki.jasp.20210248
Abstract FullText HTML PDF(3565KB) icon397 icon113
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Through analysis of multi-stage brush seal interstage pressure drop distribution characteristic theory，a new brush seal structure of differential stage was presented，and based on the fluid-structure interaction method，a new multi-stage brush seal three-dimensional entity model at all stages was established to build a new multi-stage brush type seal leakage flow characteristics experiment device；through numerical and experimental research under the different working conditions，the effects of structural parameters on pressure drop equilibrium and leakage characteristics of a new type of multi-stage brush seal were analyzed.The results showed that the standard deviation of the equilibrium ratio of pressure drop between different stages of the traditional multi-stage brush seal structure was 8.41，and that of the equilibrium ratio of pressure drop between different stages of the new structure was 4.69 and 2.07.Compared with the traditional structure at each stage，the new differential multi-stage brush seal with the increasing area of the downstream stage can effectively improve the imbalance of pressure drop between stages.Increasing the backing plate protection height could bring about the minimum standard deviation of the equilibrium of pressure drop ratio between different stages of the new structure，and the pressure drop ratio between different stages was close to each other，which can significantly improve the equilibrium of pressure drop between different stages of the new structure.Reducing the thickness of the brush bundle and increasing the clearance between the brush bundle and the rotor surface could make the leakage of the new multi-stage brush seal increase obviously.
Combined fatigue life prediction and experiment verification for turbine blade
YOU Yu, XU Jian, YAN Qun, ZHANG Wei, GUO Dingwen, HUANG Taiyu
2022, 37(5): 946-953. doi: 10.13224/j.cnki.jasp.20210019
Abstract FullText HTML PDF(1253KB) icon762 icon217
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In order to solve the fatigue strength problems of turbine rotor blade under the combined loads of temperature,centrifugal force and aerodynamic/acoustic,the decomposition method of a high-low cycle complex load spectrum and the full-time domain creep damage cumulative model based on the high-low cycle complex load were investigated.The combined fatigue life prediction method considering simultaneously the fatigue damage of creep,low cycle and high cycle was proposed.Meanwhile,the high-low cycle complex fatigue experiment platform was developed through application of the critical technologies,such as orthogonal loads decoupling and coordinated loading control of the complex load.Finally,taking a simulation specimen of a turbine blade as the research object,the combined fatigue life prediction and experiment verification were accomplished.Results showed that the scatter factor of experiment result of combined fatigue life was 1.01,and the deviation between the prediction result and the experiment result was less than 24%.The validity of fatigue life prediction model was verified,providing an effective technical approach to fatigue strength design and validation for aero-engine hot-end components.
Experiment study on predicting burst speed of disk by modified average stress method
CHEN Yanyan, QIN Shiyong, SUN Haihe, WEI Dasheng, DU Wenjun, PANG Yanlong
2022, 37(5): 954-963. doi: 10.13224/j.cnki.jasp.20210651
Abstract FullText HTML PDF(1421KB) icon283 icon91
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Based on the modified average stress method，the effects of the profile dimension parameters of TC17 titanium alloy compressor disk on the radial and circumferential burst speed were analyzed，and the transformation of burst mode was predicted.Furthermore，the test disks for radial burst mode were designed，and burst tests of TC17 titanium alloy compressor disk were carried out.The test results of disk burst are in good agreement with the calculated results of the modified average stress method.The error between the calculated burst speed reserve and the test results decreases from 7.24% before correction to 0.72% after correction，which can provide a basis for engineering application.
Workable mode design and experimental verification of aero-engine low-pressure rotor system
HUANG Jiangbo, LIAO Mingfu, LEI Xinliang, LI Ming, ZHOU Xuan
2022, 37(5): 964-979. doi: 10.13224/j.cnki.jasp.20210578
Abstract FullText HTML PDF(3301KB) icon622 icon70
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A dynamic model of aero-engine low-pressure flexible rotor with elastic supports and dampers was established，the modal and critical speed responses were calculated.Under the condition of considering the constraint of critical speed and the constraint of “critical following”phenomenon，the influence factors of modal imbalance，the proportion of spring-supported strain energy，and the stability of the sleeve-tooth connection structure were synthesized to construct a tolerance evaluation function，and a “workable mode” optimization design method for the low-pressure rotor system was established.The low-pressure rotor experimental system was designed and established，and the reliability of the design method was verified from the modal test experiment，damper damping experiment and long-term “resonance” experiment.The study results indicated that the maximum error between the calculated critical speed and the actual measured critical speed did not exceed 3.86%.The maximum damping ratio of the damper at the first and second critical speeds can reach 45.6%.The experimental rotor system completed 412.5 s and 429.8 s “resonance” experiment at the first and second critical speeds，and the rotor system of each channel vibration peak kept stable within 100 μm during the resonance process without sub-harmonic generation.The results show that the established optimization design method of “capacity mode” for aero-engine low-pressure rotor system is feasible.
Residual life prediction of rolling bearing under multiple stresses
QIU Ming, NIU Kaicen, LI Junxing, LI Yanke, XU Yanlei
2022, 37(5): 980-988. doi: 10.13224/j.cnki.jasp.20210246
Abstract FullText HTML PDF(1296KB) icon444 icon97
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In order to realize the residual life prediction of rolling bearings under multiple stresses，a method for residual life prediction of rolling bearings based on acceleration model and Bayesian theory was proposed by effectively utilizing the degradation data under no stresses.The validity of the rolling bearing test data was analyzed by goodness of fit test and Weibull probability graph test.Switching Kalman filters （SKF） were used to determine the degradation state of the rolling bearing at each moment.When rolling bearing entered into the accelerated degradation，degradation process of bearing was fitted with exponential model，and the generalized linear logarithmic model was used to represent the relationship between degradation model parameters and stress；according to the revised bearing real-time degradation data，the model parameters were updated using Bayesian algorithm，the probability density function of the residual life of rolling bearing were acquired for residual life prediction of the rolling bearing.The XJTU-SY bearing data set was used for verification，and the root mean square error of the predicted results was less than 20 min，proving that the proposed method can effectively predict the residual life of rolling bearings.
Analysis of thermal characteristics of oil-cooled aviation wet friction clutch
BAO Heyun, KONG Weidi, TAN Wuzhong, HUANG Wei, ZHU Rupeng
2022, 37(5): 989-999. doi: 10.13224/j.cnki.jasp.20210107
Abstract FullText HTML PDF(2696KB) icon342 icon64
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In order to study the temperature characteristics of aviation high power density wet friction clutch under the action of oil cooling，the thermal characteristics analysis model of the waffle groove wet friction clutch was established based on the computational fluid dynamics （CFD） method；the calculation method and application method of the heat flux density on the friction pair in the wet friction clutch were studied.Using the heat flow coupling method，the heat dissipation effect of the oil was considered，and the oil and temperature distributions on each friction pair in the clutch were analyzed.The research results showed that the uneven distribution of oil on the steel disk and friction disk caused uneven temperature distribution on the steel disk and friction disk.The temperature distribution on different steel disks and friction disks was affected by the oil distribution on the disks and the thermal conductivity of the disks，showing different temperature distribution laws.
Uncertainties establishment method of friction moment on rolling bearing based on Bayesian theory and robust theory
XU Yongzhi
2022, 37(5): 1000-1009. doi: 10.13224/j.cnki.jasp.20210249
Abstract FullText HTML PDF(1639KB) icon395 icon79
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A method on basis of Bayesian theory and robust theory was proposed to solve uncertainties of time series data on unknown distribution.The method combining with median and Huber M estimate was used to analyze robust property of time series data and establish prior distribution on Bayesian theory.Uncertainties were established by inferring from prior distribution and distribution function on time series data.At the significance level 0—0.1 range，for studies of friction torque of rolling bearing，the method determined boundaries value and confidence level of friction torque，and established prior distribution on Bayesian theory.Compared with classic statistics，the method distinctly increased evaluation accuracy 0—50% under the same confidence level.Application significance of the method lied in taking robust data to establish prior distribution，and provide a establishment method of prior distribution on Bayesian theory；adopting the median and Huber M estimate method to determine confidence level and boundary value could reduce errors of subjective factors，and provide a theory to establish uncertainties on unknown distribution.
Underdetermined blind source separation based on density peak clustering for gear fault identification
LI Miaozhen, LI Shunming, LU Jiantao
2022, 37(5): 1010-1019. doi: 10.13224/j.cnki.jasp.20210233
Abstract FullText HTML PDF(2567KB) icon352 icon59
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In order to improve the noise robustness of blind source separation algorithm in estimating the number of vibration sources，an underdetermined blind source separation method was proposed based on density peak clustering.Single source points were extracted from signals preprocessed，and then the mixed matrix was estimated by clustering single source points with density peak clustering.The separated signals were obtained by reconstructing the source signals based on the compressed sensing model.In order to verify the separation accuracy and noise robustness of the proposed algorithm，the simulation signals under different signal-to-noise ratios were separated by the proposed algorithm.The results showed that when the signal-to-noise ratios was not less than 4 dB，the proposed algorithm can accurately separate the source signals，and the accuracy and robustness of the algorithm were verified.A rotating component fault diagnosis test-bench was designed to verify the effectiveness of the proposed algorithm in practical application，and the measured composite fault vibration signal was processed.The test results showed that the algorithm successfully separated the single fault characteristics of bevel gear and planetary gear from the observed signal，contributing to the fault diagnosis of rotating components in engineering.
Experiment of Reynolds number effects on subsonic compressor plane cascade
WEI Wei, REN Siyuan, MA Husheng, LI Xuechen, ZONG Youhai
2022, 37(5): 1020-1029. doi: 10.13224/j.cnki.jasp.20210252
Abstract FullText HTML PDF(1636KB) icon560 icon134
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The flow characteristics of the UKG030.3 compressor airfoil surface and the wake area were investigated in details with the varying Reynolds number，Mach number and the angle of incidences by means of decreasing the pressure of the test chamber.The surface isentropic Mach number and the total pressure loss coefficient of the airfoil with the changing Reynolds number were concluded.The experimental results showed that the whole developing process of the separation bubbles，which exhibited appearing，extending and bursting processes，came into sight behind the maximum Mach number location of the airfoil suction side with the test chamber pressure and Reynolds number decreasing.When the separation bubbles became long，the width of the wake area and the total pressure loss coefficient increased radically.However，the critical Reynolds number associated with the loss bursting was inconsistent under different conditions.When the total pressure loss coefficient and Reynolds number were divided by the corresponding coefficients of the atmosphere condition，it revealed that the location of the total pressure loss ratio bursting was near 0.4 times the ratio of the chord Reynolds number.
Effect of tip injection on aerodynamic performance of squealer tip
XUAN Liming, ZOU Zhengping, ZHAO Qiang, HUANG Lin, DU Jinlin, CHEN Yun
2022, 37(5): 1030-1041. doi: 10.13224/j.cnki.jasp.20210104
Abstract FullText HTML PDF(2356KB) icon450 icon75
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A low-speed blade profile of a certain aero-engine high-pressure turbine rotor blade obtained by similarity transformation was studied,and the effect of tip injection on the aerodynamic performance of the squealer tip under the condition of relative casing motion was discussed.The results showed that tip injection had limited effect on the aerodynamic performance of the flat tip,but it could reduce the efficiency of the squealer tip.Under the same injection condition,the squealer tip can reduce the tip leakage loss by 20% compared with the flat tip.The energy dissipation of the leakage flow in the cavity mainly came from the interaction of the leakage flow with cavity vortex and scraping vortex.Under the injection condition,scraping vortex was still the dominant flow structure of the leakage flow.The injection position had a significant effect on the performance of the squealer tip; the jet holes near the suction side and leading edge were conducive to the improvement of the aerodynamic performance.Based on the above research,a leakage flow loss model for the squealer tip was established,and the error of new model was reduced by 31.6% compared with the Denton model.
Influence of axially-convergent contouring on cascade endwall film cooling characteristics in gas turbine
BAI Bo, LI Zhigang, LI Jun
2022, 37(5): 1042-1053. doi: 10.13224/j.cnki.jasp.20210183
Abstract FullText HTML PDF(3373KB) icon337 icon70
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In order to evaluate the influences of the axially-convergent contouring on the endwall film cooling performance of the upstream double-row film holes，the cascade endwall adiabatic film cooling effectiveness was predicted through numerical simulation.The endwall thermal load distribution，adiabatic film cooling effectiveness distribution and secondary flow field were calculated and analyzed for two endwall configurations （flat endwall and axially convergent contoured endwall） at three different blowing ratios （1.0，2.5，3.5） under the simulated realistic operation condition of an industrial gas turbine，inlet turbulence of 16%，exit Mach number of 0.85，exit Reynolds number of 1.5×106，based on “two types of thermal boundaries” numerical method.Simultaneously，the secondary cooling （phantom cooling） phenomenon of the upstream purge flow on the vane surface was noticed.Results showed that compared with the flat end-wall configuration，the axially-convergent contoured endwall reduced the strength of the horse-shoe vortex and endwall thermal load，especially at the region of vane suction surface shoulder.For the axially-convergent contoured endwall，the upstream coolant jets were more efficiently targeted at the endwall，yielding higher endwall adiabatic film cooling effectiveness，especially at the regions of the vane leading edge and vane pressure side where cooling was harder due to the stronger secondary flow.At the increasing blowing ratio，the effects of axially-convergent contouring on endwall film cooling first increased and then decreased.The axially-convergent contouring resulted in a significant increase （up to 35%） in end-wall adiabatic film cooling effectiveness at design blowing ratio of 2.5.The axially-convergent contouring obviously increased the phantom cooling size around the vane leading edge and pressure surface，especially at the region around the vane leading edge （up to 100%，0.1 span at design blowing ratio）.This led to an obvious reduction in the demand of coolant.Therefore，the axially-convergent contoured endwall is an effective approach to increase the endwall adiabatic film cooling effectiveness，reduce the demand of coolant and realize the efficient endwall cooling scheme.
Fast evaluation and analysis of Ma=8-10 vehicle mission performance based on vehicle and engine integration
ZHANG Dongqing, LI Zhengzhou, DENG Weixin, XING Jianwen
2022, 37(5): 1054-1063. doi: 10.13224/j.cnki.jasp.20210613
Abstract FullText HTML PDF(1509KB) icon469 icon149
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Targeting a flight Mach number Ma=8-10 hypersonic vehicle and scramjet，an integrated performance model of vehicle and engine was built.The model can fastly evaluate the aerodynamics of vehicle，propulsion performance of engine and flight performance.The flight performances under different take-off thrust weight ratios of 0.3，0.4，0.5 and 0.6 were compared.The optimal take-off thrust weight ratio of 0.422 was obtained，with object of minimum fuel consumption，using the MATLAB optimization tools of sequence quadratic program （SQP） algorithm based on the integrated performance model of vehicle and engine.The overall parameters of the Ma=8-10 vehicle and engine conceptual scheme were given.The total mass of vehicle was 5 943 kg with the load mass of 1 000 kg.The thrust of engine was 2 505 daN.The flight time of the vehicle was 489 s with the attack angle range of 4.1° to 3.8°.The total flight distance was 1 360 km.
Drag and heat reduction characteristics and flow mechanism of typical aero-spikes
HE Kun, YUAN Huacheng
2022, 37(5): 1064-1078. doi: 10.13224/j.cnki.jasp.20210178
Abstract FullText HTML PDF(3956KB) icon434 icon79
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In order to study the relevant characteristics of drag and heat reduction for the supersonic/hypersonic blunt aircraft with an aero-spike，numerical simulation was used to study the flow characteristics of six kinds of typical configurations of spike systematically.The influence laws of length of spike and Mach number of inlet flow on flow characteristics were given，and the mechanisms of its formation were also discussed.The results showed that when the Mach number was low，five kinds of the spikes with a flow interferent at the head reached the maximum drag reduction rates when the recirculation region was about to split； when the Mach number was high，local peaks of drag reduction rates appeared before and after the recirculation region splitting，but the maximum drag reduction rates occurred at longer lengths of the spikes after the recirculation region splitting.When the Mach number was 3，the relative lengths of the six kinds of spikes were between 0.8 and 1.2 when the drag reduction rates were maximum，in comparison，the drag reduction effects of sphere-spike，hemisphere-spike and bicone-spike were the best，the maximum drag reduction rates were between 45% and 50%；the cone-spike was the worst，which was between 20% and 25% and was obviously lower than the configurations with a flow interferent at the head.When the lengths of the aero-spikes were the same，the drag reduction rates of the aerospikes with a flow interferent at the head increased with the increase of Mach number，while that of the cone-spike was opposite.The change of pressure distribution caused by recirculation region，separation shock，bow shock and local expansion flow of the flow fields was the main reason for the change of the overall resistance of the configurations.
Predicting method of safety life of reusable liquid rocket engine turbopump
LIU Shijie, LIU Dengfeng, MA Xiaoqiu, LIANG Guozhu
2022, 37(5): 1079-1089. doi: 10.13224/j.cnki.jasp.20210420
Abstract FullText HTML PDF(1464KB) icon533 icon130
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Based on the life distribution model of complex system and fault tree analysis （FTA） theory，a safety life prediction method of turbopump was established.As an example，the safety life of the high pressure liquid hydrogen turbopump （HPFTP） of the space shuttle main engine （SSME） was verified to demonstrate this method.The results showed that：（1） The life of complex system roughly followed the exponential distribution when the number of HPFTP critical components was more than 10，and a more reliable result accompanied a larger number.（2） The mean time between failure （MTBF） and mean time to repairment （MTTR）of HPFTP was 76 917 h and 8 879 h，respectively，and the safety life of 0.998 8 reliability was 25 575 s，which can be used 49 times safely；the safety life of 0.999 6 reliability was 8 521 s，which can be used for 16 times；the reliability was 0.999 7 for 11 times safety use.（3） The key components of HPFTP safety life were turbine blade and nozzle，and their corresponding critical importance was 0.217 5 and 0.216 6，respectively，and the critical importance of both liquid collector and the impeller was 0.174 2.This work can provide a reference for the reusability research of complex components such as liquid rocket engine turbopump.
Large eddy simulation of cryogenic jet under supercritical pressure based on OpenFOAM
LI Yuhang, WU Baoyuan, WANG Yi, ZHOU Lixin
2022, 37(5): 1090-1099. doi: 10.13224/j.cnki.jasp.20210244
Abstract FullText HTML PDF(1856KB) icon481 icon112
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In order to get insights into the flow characteristics of cryogenic jet under supercritical pressure，the real-fluid model was implemented into open source CFD code OpenFOAM.The effect of real-fluid thermo-physical characteristics was introduced into the pressure correction algorithm，contributing to the development of the homogeneous solver for cryogenic flows under supercritical conditions.Transcritical and supercritical jets of LN2 were studied using large eddy simulation，including the influence of ambient temperature and pressure.The results indicated that the real-fluid model developed can describe thermo-physical characteristics accurately within wide temperature and pressure range.The homogeneous solver can correctly reveal the flow structure of cryogenic jet under supercritical conditions，which was characterized by shear layer instability and turbulent mixing.These kinds of variable density jets showed self-similarity characteristics in turbulence fully developed region.Compared with transcritical jet，the supercritical jet showed higher turbulent mixing rate and shorter core length.Under higher ambient temperature or lower ambient pressure，the density gradient between cryogenic jet and ambient gas greatly reduced，which restrained the development of instability wave in shear layer，leading to the increase of jet core length and the decrease of jet spreading angle.
Surge control system design and validation for an aero-engine
WANG Bo, ZHANG Xinglong, ZHANG Xinfei, CHE Jiexian, ZHANG Tianhong
2022, 37(5): 1100-1112. doi: 10.13224/j.cnki.jasp.20210655
Abstract FullText HTML PDF(2178KB) icon907 icon280
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In view of the problems that aero-engines were prone to surge false alarm，misjudgment and failure of anti-surge，the anti-surge effects of a single-shaft aero-engine with core drive fan stage （CDFS） at different measurement points using different signal processing methods and anti-surge control logic designs were compared and analyzed.The surge control system was verified by the fuel step forced-surge on the high altitude simulation test.The results show that the pulsation amplitude of A value at the measurement point 2 is 4 times of that at the measurement point 1，and the accuracy of surge detection by hardware is 100%.The control method by fuel step can successfully realize the engine forced-surge，and the anti-surge control logic can successfully make the engine surge exit and restore to the present state.
Evaporation processes from nanoporous membranes
WANG Jiahao, XIA Guodong, LI Ran, MA Dandan
2022, 37(5): 1113-1120. doi: 10.13224/j.cnki.jasp.20210247
Abstract FullText HTML PDF(1197KB) icon407 icon75
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Tests were conducted to study the evaporation processes from nanoporous membranes using FC-72.The heat transfer characteristics of two facing directions：membrane facing upward and downward，were compared.Results showed that the heat flux-superheat curves for two directions presented a similar variation trend，and there existed a‘thin film evaporation’ stage where heat flux increased while temperature remained constant.The temperature was stable in low heat flux.The heat transfer performance of downward-facing membrane was better than that of upward-facing membrane at different heat flux levels.This was caused by the effect of gravity on the liquid supply and the effect of liquid film thickness on thermal resistance.As the heat flux increased，the temperature fluctuated more sharply，eventually a temperature peak appeared.The critical heat flux reached 59 W/cm2 and 47 W/cm2 for downward and upward facing membranes，respectively.Additionally，theoretical modeling of the evaporation processes was carried out，and it was found that the evaporation coefficients were 0.043 1 and 0.021 9，respectively.

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