2020 Vol. 35, No. 8

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Film cooling performance of fan-shaped film hole on blade pressure side in linear transonic cascade
LI Jie, LUO Jianxia, ZHU Huiren
2020, 35(8): 1569-1577. doi: 10.13224/j.cnki.jasp.2020.08.001
Abstract PDF(4254KB) icon683 icon611
Abstract:
Film cooling performance of blade pressure side was tested in a linear transonic cascade. The film cooling effectiveness of the fan-shaped film hole on blade pressure side was measured at different mainstream inlet Reynolds numbers of 17×105, 37×105，57×105, different mainstream exit Mach numbers of 081, 091，101 and different blowing ratios of 05-30. Results showed that the mainstream exit Mach number had no distinct effect on the film cooling effectiveness at downstream film hole; however, the mainstream inlet Reynolds number had a significant effect on the film cooling effectiveness. The blowing ratio corresponding to distinguish the film’s lifting off increased with the added mainstream inlet Reynolds number, the film began to lift off at blowing ratio of 10 at mainstream inlet Reynolds number of 17×105 while these corresponding to mainstream inlet Reynolds number of 37×105 and 57×105 were blowing ratios of 20 and 25. At small blowing ratios, the case with higher mainstream inlet Reynolds number had a lager film cooling effectiveness at the region adjacent to the hole and a lower film cooling effectiveness at downstream area; however, at high blowing ratios, higher mainstream inlet Reynolds number resulted in lower film cooling effectiveness.
High frequency longitudinal combustion instability of modeled hypergolic propellants combustor,
WANG Guangxu, TAN Yonghua, ZHUANG Fengchen
2020, 35(8): 1578-1585. doi: 10.13224/j.cnki.jasp.2020.08.002
Abstract PDF(2067KB) icon632 icon566
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High frequency longitudinal combustion instability of a modeled hypergolic propellants combustor was analyzed through concentrated combustion model, in which the distribution of droplet evaporation rate along flow axis was calculated. The peak position of evaporation rate was used as the position of concentrated combustion front when the chemical time was ignored and the empirical correlation of NASA was used to provide sensitive time and interaction index. Then the model for quantity analysis of high frequency longitudinal combustion instability was built considering the hypergolic propellants droplet evaporation. Based on the curves of system oscillation gain, stability tendency under different conditions of initial droplet radius and injection velocity was analyzed. It showed that the position of concentrated combustion front was critical to high frequency longitudinal combustion instability, improvement of averaged initial droplet radius and velocity could make the front far away from the injection face, and the corresponding oscillation gain could be reduced too, making the system more stable. Especially, when the averaged droplet radius got bigger than 150 μm, oscillation gain of the modeled combustor could be smaller than 10 and the combustor could become stable in theory.
Mechanism of exhaust valve lead deposition at a certain aero piston engine
MENG Xianzhao, FENG Yanpeng
2020, 35(8): 1586-1593. doi: 10.13224/j.cnki.jasp.2020.08.003
Abstract PDF(2053KB) icon501 icon480
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In view of the serious problem of cylinder compressibility decay caused by exhaust valve lead deposited of during operation in the leaded aero gasoline condition at an aero-piston engine, based on analysis of the micro-morphology and composition of the lead deposited on exhaust valve, the formation mechanism of the pollutants on exhaust valve was analyzed in combination with the structure design and actual operating environment of this engine. Research shows that the excessive low temperature of valve operating is the fundamental cause of the pollutant deposition on the exhaust valve, and the propeller windmill factor and the design characteristic of the engine fuel system are the main reasons for the low temperature of the valve when the engine is in air idle condition. Based on this, a test scheme of reducing 200 r/min of the rotation speed of propeller in windmilling and leaning the mixture to control the exhaust gas temperature above 427 ℃ at low power status was proposed to increase the exhaust valve operating temperature, and was proved to be effective by the actual test.
Combustion performance of triple swirler combustor in ignition stage
MO Da, WAN Bin, WANG Xinzhu
2020, 35(8): 1594-1600. doi: 10.13224/j.cnki.jasp.2020.08.004
Abstract PDF(2622KB) icon625 icon487
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In order to study the ignition and flameout performance of triple swirler combustor, experiments of single-head combustor were carried out on ground and high altitude. The high altitude ignition performance at negative temperature was measured. The ground ignition process was photographed by means of high-speed camera. Combustion efficiency of ground ignition was measured by gas analysis method. The ignition and flameout performance, the ignition combustion efficiency and the ignition process of single-head combustor were obtained. Results showed that the triple swirler combustion structure had good ignition and flameout performance over a wide range of flow velocity in the primary zone. The fuel burnt efficiently and the ground ignition combustion efficiency was about 80%. The negative temperature increased the difficulty of ignition. Compared with the normal temperature ignition boundary, the negative temperature ignition boundary narrowed by 188%-375% when the pressure was 70 kPa. High altitude flameout boundary was close to ignition boundary. The experimental results provide an important reference to the design of the triple swirler combustor.
Influence of axial and circumferential lengths of combustion chamber on gas-liquid two-phase rotating detonation characteristics,
LI Baoxing, XU Guiyang, SHU Huiming
2020, 35(8): 1601-1611. doi: 10.13224/j.cnki.jasp.2020.08.005
Abstract PDF(4383KB) icon585 icon463
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In order to study the influences of axial and circumferential lengths of rotating detonation engine combustion chamber on gas-liquid two-phase rotating detonation characteristics, the theoretical model of gasoline/oxygen-enriched air two-phase rotating detonation with chemical reaction was solved by conservative element and solution element (CE/SE) method. The flow field structure of gas-liquid two-phase rotating detonation was obtained, and the influences of the axial and circumferential lengths of the combustion chamber on the flow field, detonation wave propagation characteristics and thrust performance of the engine were analyzed. The calculation results showed that the axial length had little effect on the upstream flow field of the combustion chamber, but had a significant effect on the downstream flow field parameters. With the increase of the axial length, the outlet pressure, temperature, density and circumferential velocity of the combustion chamber decreased, while the axial velocity increased gradually, and the average thrust density and fuel specific impulse of the engine increased first and then decreased. When the circumferential length was too short, it was difficult to form a self-sustaining propagating detonation wave in the combustion chamber. As the circumferential length increased, the strength of upstream detonation wave increased, and the corresponding flow field parameters increased, however, the thrust performance of engine decreased slightly.
Effect of different hole shapes on hypersonic counter-jet film cooling
SHANG Shengfei, XIANG Shuhong, JIANG Lixiang
2020, 35(8): 1612-1621. doi: 10.13224/j.cnki.jasp.2020.08.006
Abstract PDF(6077KB) icon542 icon453
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The influences of different cooling holes at different mass flow rates on film cooling effect were studied by researching the relationship between the film cooling hole shape and counter jet flowing. The CFD method was used to study 4 kinds of working conditions of the cylindrical hole, the shrinkage hole, the expansion hole and the shrinkage-expansion hole under flight height 50 km, flight Mach number 15 condition. Results show that: under the small mass flow rate, long penetration model (LPM) will occur in the shrinkage hole and the cylindrical hole, unlike the case of the expansion hole and the shrinkage-expansion hole. With the increase of the jet mass flow rate, the jet will change from LPM mode to short penetration model (SPM) mode, and the cooling benefit will not appreciably increase with the increasing jet mass flow rate. Considering the changes of the whole working states, the expansion hole is a relatively stable and reliable film cooling hole in the counter-jet film cooling.
Effect of temperature on water production performance of oxygen-consuming inerting system,
PENG Xiaotian, FENG Shiyu, ZHOU Libiao
2020, 35(8): 1622-1627. doi: 10.13224/j.cnki.jasp.2020.08.007
Abstract PDF(2210KB) icon506 icon374
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Based on the gas molar flow rate at fuel tank outlet, the molar flow relationship between the gas components flowing through the catalytic reactor and the cooler was deduced, and a mathematical model of the oxygen-consuming inerting system was established. The effect of ambient temperature on “water” performance in the system was studied. Results showed: as the inerting developed, the proportion of water vapor on fuel tank ullage gradually increased, while the amount of cooling air, the relative humidity at the reactor outlet and the amount of removed water decreased. The impact of liquid water precipitation on cooling air amount was huge and cannot be ignored. In addition, the generation and precipitation of water in the system were related to the ambient temperature. The lower ambient temperature indicated the slower rise of water vapor volume on fuel tank ullage, but more cooling air required by the system and the greater amount of precipitating liquid water. For example, when the ambient temperature was 0 ℃, the amount of cooling gas required in the cooler was about 111 times and 126 times of that at 20 ℃ and 40 ℃, respectively.Therefore, when designing an oxygen-consuming inerting system, the effect of temperature changes on the generation and precipitation of water should be fully considered.
Influence of different geometric structures on thermal protection characteristics of fuel nozzle
LIU Tianchi, FAN Yuxin, WU Weiqiu
2020, 35(8): 1628-1642. doi: 10.13224/j.cnki.jasp.2020.08.008
Abstract PDF(6997KB) icon508 icon443
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The deposition performance of tubes with different structures was studied experimentally, And the results showed that when the inflow temperature, inflow velocity, fuel inlet temperature and velocity was 1 000 K, 150 m/s, 400 K and 05 m/s, the test pieces with smaller angles and expansion sizes had less deposition on the tube wall, and the amount of deposition fluctuated with the increase of time during the initial stage of heating. The amount of deposition on the tube wall reached the maximum when heating for 15 minutes, and then the removal of a part of deposition caused the reduction of deposition measured. The influence of fuel nozzle and nozzle cap with different geometric structures on thermal protection characteristics was studied by means of numerical simulation and experiment. Results showed that the fuel nozzle with concentric arrangement of primary and secondary fuel passages had the best thermal protection effect, which could reduce the maximum wetted wall temperature by nearly 50% under test conditions, even better than the model with air gap. Reducing the contact area between the nozzle cap and the nozzle body or filling the materials with low thermal conductivity were effective improvement measures, which could reduce the outlet oil temperature by about 5 K. The results of this study have guiding significance for the design of fuel nozzle thermal protection.
Experiment on the influence of fuel temperature on the atomization characteristics of centrifugal nozzles,
WANG Jiajun, GUI Tao, QIU Wei
2020, 35(8): 1643-1654. doi: 10.13224/j.cnki.jasp.2020.08.009
Abstract PDF(5986KB) icon606 icon479
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The atomization characteristics of three types of centrifugal nozzles’ injection into static atmosphere at the head of a central staged combustion chamber’s auxiliary oil passage were experimentally studied. The influences of different injected fuel temperature (-40~80 ℃) and fuel supply pressure difference on the fuel atomization characteristics were obtained. Phase Doppler particle anemometry （PDPA） was used to measure the spray mist characteristics on the plane 30mm away from the nozzle exit along the flow direction, and the laser particle size analyzer was used to further verify the experimental results. The results of the experimental study were given as follows: (1) the flow number of the centrifugal nozzle gradually decreased with the increase of the fuel temperature, and decreased sharper in the low temperature section. (2) The Sauter mean diameter (SMD) in the diameter on the measuring plane decreased with the temperature rise in the low temperature section, while the decrease was sharper at the center of the fuel spray cone. (3) The particle size distribution of the spray field measured by the laser particle size analyzer verified the accuracy of the PDPA measurement results to a certain extent. The droplet characteristic diameter and the droplet size distribution coefficient decreased with the increase of the fuel supply pressure difference.
Characteristics of premixed swirling tubular flame under acoustics perturbation,
YU Xiao, ZHAO Xiaoyao, MA Kang
2020, 35(8): 1655-1663. doi: 10.13224/j.cnki.jasp.2020.08.010
Abstract PDF(3452KB) icon478 icon418
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To investigate the combustion instability of the premixed swirling tubular flame, the responses characteristics of methane/air premixed flames to longitudinal acoustic field was experimentally studied with different air volume flow rates and methane equivalent ratios. The dynamic response range of flame to different acoustic frequencies was revealed,and the variation of flame structure,acoustic pressure and OH* fluctuations under acoustics perturbation were studied. The results showed that the flame presented the low-pass filtering characteristic, demonstrating very weak response to the high acoustic frequency. For middle and low acoustic frequency, the flame was forced to oscillate at the same frequency, and even quenched at a lower acoustic frequency. In addition, the low-pass filtering behaviors were slightly affected by the flow rate and equivalent ratio. According to the calculated extinction strain rate, near lean extinction limit (eg, equivalence ratio equaling to 065), the flame was much sensitive to middle acoustic frequency owing to low extinction strain rate, generally presenting flame lift-off.
Fusion model prediction of rolling bearing vibration signal based on chaos theory,
MENG Fannian, DU Wenliao, LI Hao
2020, 35(8): 1664-1675. doi: 10.13224/j.cnki.jasp.2020.08.011
Abstract PDF(5059KB) icon576 icon434
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The fusion algorithm model was used to predict the vibration signal of rolling bearing on the basis of chaos theory. Based on the phase diagram method, the maximum Lyapunov exponent method and the correlation dimension method, the chaos characteristic of rolling bearing vibration signal was proved. The weights of Kriging model, least squares support vector machine（LSSVM）model and extreme learning machine（ELM）model were optimized to minimize the norm of the difference between the predicted value and the true value, and the fusion algorithm model was constructed by weighting method. The phase space reconstruction method was used to construct the training samples of the rolling bearing vibration signal prediction, and the fusion model, Kriging model, LSSVM model and ELM model were trained. The trained model was used to predict the vibration signal of rolling bearing. For case 1 and case 2, the rolling bearing vibration signals of two experiments were used to verify the results. The maximum Lyapunov exponent for two cases was greater than 0, from which chaotic characteristic on bearing vibration signal can be determined. Besides, the index value for fusion model was less than the single model from the evaluation index of mean squared error, root mean squared error and mean absolute error, so the prediction accuracy of the fusion algorithm model was better than that of the single algorithm model.
Contribution analysis of vibration transfer paths in encased differential planetary train
LI Miaomiao, LIU Qinwen, YANG Jie
2020, 35(8): 1676-1686. doi: 10.13224/j.cnki.jasp.2020.08.012
Abstract PDF(5617KB) icon591 icon434
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In response to the requirements of the encased differential planetary train in terms of vibration reduction and noise reduction, a method for contribution analysis of vibration transfer paths was proposed. Taking the time-varying meshing stiffness and error equivalent displacement generated during gear meshing as internal excitation, the vibration transfer path of the encased differential planetary train was analyzed, and the contribution of each vibration transfer path was discussed based on the power flow method. Results showed that, the vibration receiving structure including the output shaft, the differential stage sun gear and the encased stage star gear at the maximum resonance frequency corresponded to the maximum common amplitude values of 14 010,3 314，95 180 (m/s2)/Hz, respectively. According to the conclusion, the path 4 including the encased stage ring gear and the output shaft had a vibration transfer path contribution percentage of 777%, 775%, 786% and 699%, respectively, under the differential stage external meshing excitation, differential stage internal meshing excitation, encased stage external meshing excitation and encased stage internal meshing excitation. The encased stage ring gear and output shaft play a major role in the vibration transmission of the encased differential planetary train.
Dynamic characteristics of spiral bevel gear considering tooth surface friction
LI Fei, YUAN Ru, ZHU Huiling
2020, 35(8): 1687-1694. doi: 10.13224/j.cnki.jasp.2020.08.013
Abstract PDF(2865KB) icon491 icon270
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Based on the centralized parameter method, an 8 degrees of freedom dynamic model and dynamic equations of spiral beveled bevel gears were established. Considering the static transmission error, tooth surface friction and tooth clearance comprehensively, the dynamic responses of transmission system were solved by Runge-Kutta algorithm with variable step lengths, and the effects of friction coefficient and coincidence degree on the vibration amplitude of the transmission system were studied. The results showed that the friction coefficient was different under different working conditions. With the decrease of lubricating oil, the friction coefficient, the system’s vibration displacement and normal meshing force increased; coincidence degree was reduced, but vibration amplitude and normal meshing force increased while the angle between the contact trace and the root cone increased.
Comparison on flow field characteristics of four wind tunnel contraction sections
GAO Limin, LIU Zhe, CAI Ming
2020, 35(8): 1695-1705. doi: 10.13224/j.cnki.jasp.2020.08.014
Abstract PDF(5532KB) icon575 icon439
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Based on the high subsonic linear cascade wind tunnel of Northwestern Polytechnical University, the outlet flow field of Witozinsky contraction section was measured, and the poor directional field quality was found. Besides, the core area was reduced by 15% at pitchwise compared with the velocity and total pressure fields. Then exit core area, uniformity and separation characteristics of four contraction sections were compared by simulation. It was found that Witozinsky curve contracted at front, and contracting too fast caused vortex at inlet, but the outlet uniformity was better due to the longer outlet steady flow section. In contrast, double cubic curve mainly contracted at rear with greater forward pressure gradient of mainstream, so there existed thinner boundary layer, smaller deviation angle and better separation characteristics. The existing three-dimensional structure of Witozinsky contraction section widens the core area while disturbing airflow, deteriorating the velocity and direction fields, and increasing the deviation angle up to 43%. The inlet pipe diameter has little effect on the flow field characteristics of the double cubic contractions.
Prediction and test verification of inlet distortion based on flight test data
JIANG Jian, ZHAO Haigang, LI Junhao
2020, 35(8): 1706-1715. doi: 10.13224/j.cnki.jasp.2020.08.015
Abstract PDF(2266KB) icon551 icon302
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Experimental design of response surface methodology was adopted to construct the inlet pressure distortion prediction model based on flight test data, while the inlet distortion model prediction and flight test verification were studied under different flight conditions. The results showed that, compared with the flight test results, the model prediction average relative error of the comprehensive pressure distortion index was 421%, and the average relative error of the steady-state circumferential distortion index was 799%, which were in agreement with each other and can meet the requirement of the inlet distortion prediction. At large angle of attack, sideslip and combined flight conditions, the flow separation of the boundary layer inside the inlet contributed a lot to the distortion of the inlet outlet. The position of the inlet outlet low pressure zone corresponded to the flight attitude angle, and there was a small range of deflection in the direction of the compressor rotation in the circumference direction, and the deflection angle was related to the engine state. The model of “model prediction+flight test” can be used to evaluate the distortion characteristics of aircraft inlet completely, safety and efficiently, and it has good engineering practicability.
Test of high-bypass-ratio turbofan engine jet noise reduction
LIU Changchun, GAO Kang, ZHOU Xunhuang
2020, 35(8): 1716-1723. doi: 10.13224/j.cnki.jasp.2020.08.016
Abstract PDF(3149KB) icon571 icon314
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A scale model test of high-bypass-ratio separated exhaust nozzle was conducted on the jet noise test facility for simulating a dual-stream hot flow to provide far-field noise characteristic of the turbofan engine. A baseline axisymmetric nozzle and four chevron nozzle were tested and analyzed to provide insight into some basic mechanisms and trends of this technology. Spectral and directivity results showed that high-bypass-ratio jet noise was mainly dominated by low frequency component generated by large scale turbulence, leading to the maximum directivity in 150 degree. Chevron nozzle was most effective at lower frequencies and at aft directivity angles, and the nozzle was shown to produce peak sound pressure level (SPL) reduction up to 6 dB. Penetration of chevron can significantly affect the noise reduction. Bypass chevron configuration with high penetration provided the best noise reduction among four chevron configurations, and the maximum over-all sound pressure level (OASPL) attenuation was 3 dB. Core chevron configuration reduction was less than bypass chevron configuration, in which the maximum OASPL attenuation was less than 1 dB. The combination of core and bypass chevron can lower SPLs compared with bypass chevron, and the maximum OASPL reduction was 17 dB.
Destabilizing factors on surge and stall characteristic in aero-engine airworthiness certification
QI Lei, LI Zhiping, YANG Dong
2020, 35(8): 1724-1734. doi: 10.13224/j.cnki.jasp.2020.08.017
Abstract PDF(6711KB) icon716 icon355
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Combining aerothermodynamics theory with engineering problems in the airworthiness field, the representative destabilizing factors of engine surge and stall characteristics were investigated systematically. A fast method of surge/stall margin prediction was established, based on which the destabilizing factors and their laws of JT9D engine model were studied. Results showed that the most important factor affecting the stability margin of fan components was distortion, and the most important factor affecting the stability margin of booster stage and high-pressure compressor was structural decay during the lifetime. The related key elements of CCAR 3365 compliance verification activities have been confirmed. The compliance verification process of CCAR 3365 has been improved, providing a technical support for airworthiness certification ability improvement.
Risk model in conceptual design phase of civil aero-engine type certification
ZHANG Gong, HE Xin, FENG Jianwen
2020, 35(8): 1735-1743. doi: 10.13224/j.cnki.jasp.2020.08.018
Abstract PDF(1544KB) icon459 icon283
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A systematic working mechanism for risk identification in conceptual design phase of civil aero-engine was established to promote efficient type certification with corrective actions. The mechanism comprehensively categorized the risks of regulations, means of compliance, implementations and critical technical points, by which the regulation terms information table was developed. 278 potential risks were identified by regulation terms information table utilization in specific civil aero-engine model. In addition, the potential risk of typical rotor integrity regulation in process from requirement definition to design implementation was analyzed in detail, which verified the mechanism and regulation terms information table.
Effect of freezing temperature on mechanical properties of hail in airworthiness test
GE Xin, ZHANG Lifen, LIU Zhengxia
2020, 35(8): 1744-1751. doi: 10.13224/j.cnki.jasp.2020.08.019
Abstract PDF(4382KB) icon414 icon282
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In order to study the mechanical properties of cotton-containing hail in the test standard for transparent enclosures of aviation aircrafts (ASTM-F320-2010) and pure ice hail in aero-engine hail suction test, the hail mold was designed and manufactured. Based on natural hail freezing temperature, the hails were made in different temperatures and compressed in a universal testing machine. The quasi-static compressive strength data and the relationship between the freezing temperature and the mechanical properties were obtained. Results showed that the average compressive strength of pure ice hail increased slightly about 2 MPa when the freezing temperature changed from -10 ℃ to -30 ℃; meanwhile the average maximum compressive strength of cotton-containing hail did not show significant change within this temperature range; the temperature dropped to -40 ℃, the average compressive strength of both hail increased significantly, and pure ice hails were more sensitive to temperature, and the rise was more significant. It is proposed that the test hail produced at -40 ℃ can be added to the consideration of the airworthiness test of future commercial aviation engines and large civil aircraft in China.
Blades flutter of non-zero inter-blade phase angle based on vibration time-delay method
DU Yunxiang, XU Zili, JIAO Yuxue
2020, 35(8): 1752-1761. doi: 10.13224/j.cnki.jasp.2020.08.020
Abstract PDF(4260KB) icon515 icon341
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A vibration time-delay method of setting inter-blade phase angle by means of delayed blade vibration and a fluid-structure interaction flutter analysis model for multiple passage blade non-in-phase vibration were developed. The number of passages was twice the passages between adjacent nodal lines; and in the different passages of the cyclic sector, the modal displacement of each blade lagged behind that of the previous blade, and the efficient update of the flow field and blade grids was realized using the fast dynamic mesh algorithm based on pseudo elastic solid. Based on the multiple passage model of Rotor 37, the influences of different inter-blade phase angles on the aerodynamic stability of blades and the flow field characteristics of passages were studied. The results showed that the calculation result of the multiple passage method was basically consistent with the full annulus flutter analysis, and the calculation time of the multiple passage method was 1486% of the full annulus analysis at 18 nodal diameter. Nodal diameter pattern had a significant influence on the aerodynamic damping of blades, and flutter instability occurred at 2 nodal diameter. The inter-blade phase angle led to the changes of the shock wave location and strength and the unsteady pulsation and impact out of phase in the passage, contributing a lot to the flutter.
Creep behavior of titanium alloy with thermal barrier coatings
BAI Yu, WANG Chun, ZHAO Bin, ZHANG Tingting, XIA Tian
2020, 35(8): 1762-1767. doi: 10.13224/j.cnki.jasp.2020.08.021
Abstract PDF(1979KB) icon543 icon270
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With the aim of improving the creep resistance of titanium alloy, NiCrAlY (bond coat, BC)/yttria stabilized zirconia (top coat, TC) thermal barrier coatings (TBCs) were deposited on TA32 substrate,and the creep resistance of titanium alloy with TBCs was studied by test and numerical simulation.The results showed that there was a large difference between the creep rate of TA32 and that of TBCs. TC had an obvious constraint effect on the creep deformation of TA32 during tensile process at high temperatures, and the axial tensile stress of NiCrAlY BC in TBCs was larger than other parts. At 400 ℃ and 600 ℃, TBCs improved the creep resistance of TA32 by 56% and 175%, respectively. However, when the test temperature reached 600 ℃ and the tensile stress reached 200 MPa, severe cracking or peeling occurred in TC.
Time-frequency analysis of unsteady flow in centrifugal compressor
WU Wei, ZHAO Bo, XUE Xiang
2020, 35(8): 1768-1776. doi: 10.13224/j.cnki.jasp.2020.08.022
Abstract PDF(4548KB) icon597 icon303
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Improving the reliability of centrifugal compressor operation requires accurate acquisition of time-frequency characteristics. Based on the dynamic pressure data acquired at the impeller outlet when the high-speed centrifugal compressor with vaneless diffuser approached the unsteady condition, spatiotemporal intrinsic mode decomposition (STIMD) and empirical mode decomposition (EMD) were used to obtain the intrinsic mode functions (IMF). Combining Hilbert transform, the dynamic characteristics of unsteady flow were analyzed. By STIMD algorithm, the time-frequency information of deep surge and mild surge was obtained. The phenomenon of stall with continuous fluctuation frequency around 150 Hz was observed, whilst the transition of frequency curve of mild surge precursor from oscillating to constant state was found. STIMD algorithm has improved the modal aliasing problem of EMD, thus providing a tool for compressor stability analysis.
Modeling and frequency characteristics of jet-pipe servo valve considering eddy current effect
YIN Yaobao, GUO Wenkang, HU Yuntang
2020, 35(8): 1777-1785. doi: 10.13224/j.cnki.jasp.2020.08.023
Abstract PDF(3991KB) icon437 icon313
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Considering the problem of response lag of jet pipe servo valve in the process of electric-magnetic-force-displacement conversion, a mathematical model of torque motor considering eddy current effect was established, and the dynamic characteristics of torque motor were obtained. Taking a certain type of jet tube flow servo valve as an example, a mathematical model of jet pipe servo valve considering the eddy current effect was established. The influence of main parameters on the frequency characteristics of the servo valve was obtained. Among them, the increase of air gap length, air gap magnetic permeability, and decrease of air gap effective area caused the servo valve to respond slowly, the number of control coil turns did not affect the frequency characteristics of the servo valve; decreasing the conductivity of the magnetically conductive material can increase the response speed of the servo valve. The servo valve was tested, the difference between the theoretical value and the test value was about 5%, verifying the correctness and effectiveness of this model.
Effect of short-shell insulated area on thermal insulation performance of liquid hydrogen tank
HU Zhenggen, ZHAN Lihua, ZHU Wenli
2020, 35(8): 1786-1792. doi: 10.13224/j.cnki.jasp.2020.08.024
Abstract PDF(1805KB) icon347 icon282
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Based on the computational fluid dynamics (CFD) method, the effect of the magnitude of typical 5 m diameter tank short-shell insulated area (non adiabatic, 50% adiabatic and 100% adiabatic) on the evaporation characteristics of liquid hydrogen tank was studied. The volume of fluid (VOF) model was used to calculate the two-phase flow with the Lee model for calculations of the mass transfer rate in the gas-liquid interface. The heat transfer boundary conditions due to possible frosting on the foam surface and the bare metal surface were considered. The numerical model and the interface mass transfer calculation had clear gas-liquid interface, and helped to accurately capture the change of liquid hydrogen level. The numerical results showed that short-shell was the main factor of heat leakage in liquid hydrogen tank and played an important role in the effect of liquid hydrogen evaporation rate. The average temperature of the gas phase decreased from 110 K in 0 case to 32 K in 50% case, while it only decreased to 23 K when the adiabatic area continued to increase to 100%, and the improvement effect of the adiabatic area was relatively reduced. Compared with the effect of the increase of the adiabatic proportion of short shell from 50% to 100% and from 0 to 50% on the relative evaporation rate, the difference of the former was small, only 24%, while the difference of the latter was obvious, with a decrease of 409%. The research results provide a guide to the optimization design of the thermal insulation structure of the liquid hydrogen storage tank.

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