2020 Vol. 35, No. 7

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Disturbance characteristic of underwater salvo
BI Fengyang, LU Bingju, ZHAO Shiping
2020, 35(7): 1345-1352. doi: 10.13224/j.cnki.jasp.2020.07.001
Abstract PDF(2478KB) icon510 icon679
Abstract:
Focusing on the multiphase flow with heat and mass transition and the motion coupling process of underwater vertical salvo, a numerical calculation model of multiphase flow, slender body motion and deformation load of the adapter module was established to study the characteristics of salvo interference. The results showed that the lateral fluid load and the deformation of adapter module influenced the launching trajectory significantly. In the course of launching, the lateral displacement reached 01 times the length of the body and the lateral attitude angle reached 7°. In addition, the flow backward and bubble overflow process of canister outlet after the launch of the first slender body had a significant influence on the bubble shape, load state of the second slender body, as well as the trajectory. In the current case, the difference of lateral attitude angle between the first and second launching bodies is about 01° at the leaving moment, and the difference of angle velocity reaches 75 (°)/s.
Analysis on isotropy and sensitivity of vector thrust stand
WU Feng, YUAN Zhanbin, ZHANG You
2020, 35(7): 1353-1360. doi: 10.13224/j.cnki.jasp.2020.07.002
Abstract PDF(1056KB) icon641 icon665
Abstract:
The isotropy and sensitivity analysis was conducted to design and optimize the structure of vector thrust stand. Given the closely interlinked isotropy and symmetry, symmetric distribution of load cells was denoted, and the associated characteristic equations about their coordinates were proved.By condition number based on spectral norm of first order static coefficient matrix,the isotropy features of six-component stand were analyzed in detail. It was proved that 2∶2∶2 configuration can realize perfect isotropy and 3∶2∶1 configuration can only realize isotropy of torque.After optimizing radius and angles,the ideal configurations were obtained for each case respectively.The ideal 2∶2∶2 configuration was rx=ry=rz with (θx,θy,θz)=(0,90°,180°) or (90°,180°,270°) and ideal 3∶2∶1 configuration was rx=3rz/2 with θx=0°. Comparing the difference between real and ideal configurations and studying associated sensitivity,it was found that the isotropy of force or torque led to the isotropy of corresponding sensitivity.The force and torque sensitivity were proportional to the flexibility of the elastic rod,while the torque sensitivity was inversely proportional to the distribution radius of the related cells.Above methods and conclusions are instrumental in design and construction of vector thrust stand.
Numerical simulation about starting process characteristics of hypersonic wind tunnel
CONG Chenghua, REN Zebin, LI Song
2020, 35(7): 1361-1368. doi: 10.13224/j.cnki.jasp.2020.07.003
Abstract PDF(3098KB) icon528 icon741
Abstract:
In order to obtain the characteristics of the flow field structure changes during the starting progress of the hypersonic wind tunnel, two-dimensional axisymmetric model was used to study the flow field characteristics of the nozzle section, test section and diffuser section of the Φ05 m high speed wind tunnel. The governing equations were the conservational Navier-Stokes equations, which described viscous, compressible and unsteady flows. The establishment process of flow field at test section Mach number 5, 10 was compared, and the results showed that the boundary layer in the nozzle was very thick, and the complex shock structure was formed by the interaction of shock wave and boundary layer. When test section Mach number was 5, a positive shock wave was formed in the nozzle section. When the test section Mach number was 10, a shock wave string was formed from the nozzle section. The starting pressure ratio was lower than that calculated according to the positive shock theory. The starting speed of the shock wave string was slower than that of the positive shock, but its stability was better than that of the positive shock. During the starting process, the flow underexpanded excessively, and the instantaneous Mach number of the wave front was much larger than the design Mach number of the nozzle. The free jet at the exit of the nozzle and the collector played a complex role. The overfall of the collector played a key role in establishing a stable flow in the test section.
Noise control of a local-resonant acoustic metamaterials,
L Haifeng, WANG Puhao, YE Junjie
2020, 35(7): 1369-1375. doi: 10.13224/j.cnki.jasp.2020.07.004
Abstract PDF(2207KB) icon767 icon720
Abstract:
In order to control the wide-band noise, An acoustic metamaterial with both Helmholtz resonance and spring mass system resonance and its control method were proposed.. The double local resonance system was equivalent to the series connection of two spring mass systems. Theoretical results showed that two local resonance band gaps can be generated in the double resonance acoustic metamaterials. The correctness of the mathematical model was verified by the Finite Element Method. Based on the comparison of the influences of resonant volume and membrane tension on the transmission loss of the system, the pneumatic modulation was selected to control the tension of the membrane and then the transmission loss. The measurement indicated that, when the driving air pressure increased from 0 to 2 kPa, the first transmission loss peak of the system kept almost constant while the second transmission loss peak shifted 150 Hz to the high frequency. The designed local resonance acoustic metamaterials have good control effect on low-frequency noise in the band gap range, thus providing a method for adaptive control of broadband noise.
Design of supersonic axisymmetric variable geometric inlet with zero additional drag
NAN Xiangjun, ZHANG Hao
2020, 35(7): 1376-1382. doi: 10.13224/j.cnki.jasp.2020.07.005
Abstract PDF(2216KB) icon513 icon579
Abstract:
In order to solve a difficult problem of inlet that its compression doesnt well match with free Mach number within large Mach number range, an inlet with total mass capture was explored. Theory relations that should be met in inlet design process were obtained according to aerodynamics analysis. Based on these relations, an inlet example was designed and its variable geometry law was gotten. Numerical simulation was used to research the flowfiled and performance of the inlet, whose mass flow rate could be over 099 from Mach number 12 to 40. Preliminary results show that an inlet with total mass flow capture within wide Mach number can be designed by matching the free Mach number, contraction ratio and variable geometry law exactly, and cowl wall shape has characteristic of “S”.
Realization and aerodynamic optimization of flat-nosed hypersonic missile integrated with an axis-symmetrical front-tip
TANG Xiao, MO Ran, CHEN Junjie
2020, 35(7): 1383-1391. doi: 10.13224/j.cnki.jasp.2020.07.006
Abstract PDF(3936KB) icon572 icon658
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In the current application of flat nosecones in the missiles, the disadvantages such as low front space use efficiency, difficulties in the manufacturing, and poor transmission performance bring about a great demand for the integration of a class function/shape function transformation technique（CST） based flat nosecone to an axis-symmetrical front-tip with a ‘front-tip-down angle’. The ‘front-tip-down angle’ was used to realize the smooth transition of the merging region. The computational fluid dynamics calculation results were obtained for the axis-symmetrical nosecone, the flat nosecone, and the integrated nosecone at ‘front-tip-down angle’ varying from 0 to 5 degree. The results showed that the maximum lift-drag ratios of the axis-symmetrical nosecones, the integrated nosecones at zero angle of front-tip-down, and the ones at non-zero angle of front-tip-down were 8158%, 8616%, and 8946%, respectively, to that of the flat nosecone. An optimization was processed in order to obtain the maximum lift-drag ratio and lift coefficient in the integrated nosecones at 2 and 3 degrees of “front-tip-down angle”. In the 2 and 3 degrees of “front-tip-down angle” cases, lift-coefficient pareto-optimal fronts increased by 599% and 416%, lift-drag ratio pareto-optimal fronts decreased by 1996% and 1839%, respectively, while the terminal radius of the axis-symmetrical front-tip increased from 150 mm to 210 mm. Furthermore, when the terminal radius was less than 165 mm, the lift-drag ratio in the configuration with 2 degrees of “front-tip-down angle” was larger (peak value could reach up to 9779% to that of flat nosecone). While the terminal radius was larger than 165 mm, the lift-drag ratio in the other one was larger.
Multi-objective optimization design of hypersonic axisymmetric inlet
WANG Changsheng, Eriqitai, DING Wenhao
2020, 35(7): 1392-1401. doi: 10.13224/j.cnki.jasp.2020.07.007
Abstract PDF(2303KB) icon669 icon686
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Taking the hypersonic axisymmetric inlet as the research object, firstly, parametric design of the inlet profile was carried out, and seven parameters, such as the general conic saturation, the general conic control line, the transition arc radius, the throat corner, the throat straight line to height ratio, the center line control parameter and the equivalent cone angle, were selected as the design variables to carry out the multi-objective design of the inlet. In the design process, the initial sample points were determined by orthogonal test design method, and Kriging surrogate models between two optimization objectives of inlet total pressure recovery coefficient and outlet distortion with design parameters were established. The surrogate model was analyzed and solved by the second generation of Non-Dominated Sorting Genetic Algorithm (NSGA-Ⅱ). The results showed that after multi-objective optimization, the total pressure recovery performance of the inlet increased by 263%, and the outlet distortion reduced by 2757%.
Random vibration response calculation and fatigue analysis of thin-walled structures under heat flux environment,
SHA Yundong, AI Size, ZHANG Jiaming
2020, 35(7): 1402-1412. doi: 10.13224/j.cnki.jasp.2020.07.008
Abstract PDF(4582KB) icon592 icon673
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For the problem of random vibration stress response variation law and fatigue failure time of thin-walled structures under high-speed heat flux environment, numerical simulation calculations and high temperature random vibration tests were carried out. By comparing the simulation results with the experimental results, the modal error was less than 28% and the stress response error was less than 4%. The structural fatigue failure time error was less than 3 430 s, verifying the reliability of the numerical simulation. Based on the coupled FEM/BEM（finite element method/boundary element method） theoretical, the Fluent software was used to simulate the high-speed heat flux environment, and the calculation of the random vibration stress response of the thin-walled structure under high-speed heat flux environment was realized. The dynamics response and fatigue failure time of thin-walled structures under different vibration magnitudes and heat flux environments were obtained. The variation law of structural thermal random vibration stress response and fatigue failure time under different environment temperatures and flux rates was analyzed, and the reasons for these changes were explained. The work completed can provide a reference for the estimation of thermal random vibration fatigue failure time of thin-walled structures under high-speed heat flux environment.
Dynamic characteristics analysis of aero engine casing structures with viscoelastic damping materials under elastic supports
WU Hongchun, HAN Qingkai
2020, 35(7): 1413-1424. doi: 10.13224/j.cnki.jasp.2020.07.009
Abstract PDF(3399KB) icon577 icon595
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The analysis approach of the casing with viscoelastic damping material treatment under arbitrary elastic supports was proposed for the requirement of the vibration control of aero engine casing. The casing was considered as a thin-wall cylindrical shell. Then the governing dynamic equation of casing treated with the constrained layer damping was established, in which the effects of shear stress due to viscoelastic damping material were considered. By introducing a series of boundary spring elements, the boundary load of the casing was transformed into the elastic potential energy of the spring, and the effective simulation of the arbitrary boundary support stiffness on the casing was realized. Results showed that the increasing boundary stiffness could improve the natural frequencies of the casing, while the sensitivity of the damping characteristics to the support stiffness was opposite to the natural frequencies. In addition, in the design process of engineering casing, the satisfactory structural dynamic characteristics can be obtained by strengthening the circumferential and normal stiffness of the supporting structure.
Method of failure mode analysis and test verification for fiber reinforced composites turbo-shaft structure
LUO Li, SHA Yundong, HAO Yanping
2020, 35(7): 1425-1436. doi: 10.13224/j.cnki.jasp.2020.07.010
Abstract PDF(3110KB) icon599 icon527
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For continuous fiber reinforced composites turbo-shaft structural failure mode analysis, based on the macro-mechanics and meso-mechanics analysis method of cross-scale, a micro-mechanics representative volume element (RVE) model was established, through programming and simulation, the periodic boundary conditions of model were realized, the stress response of fiber reinforced composites was calculated and the mean stress was converted into real stress, then the failure envelope was determined. It established mechanical model of fiber reinforced composite shaft structures, and the principal stress response was calculated. Through the transformation of the principal-partial axial stress for the composite laminated plates, the macroscopic stress response calculation results of the dangerous elements in all directions were transformed into the microscopic mechanics RVE model, reflecting the microscopic mechanics load condition of the RVE model. The failure mode of composite shaft structure at dangerous position was determined by the failure boundary of micro-mechanics; when the torsional load was between 5 000-5 500 N·m, the outermost layer of the composite, also the layer 6 (+45°), reached the tensile failure load of the matrix firstly. The failure mode test of composite shaft structure was carried out; when the torsional load had reached 6 000 N·m, acoustic emission signals stacked with each other, most of which were intermediate frequency signals, of which most were matrix and interface cracking signals. Then compared with the simulation results, it verified the effectiveness of the failure mode analysis method. The failure load and failure mode of a certain engine low pressure turboshaft have been predicted by using the proposed model.
,Unilateral wear characteristics of brush seal based on Archard model,
DONG Shuna, DU Chunhua, CUI Yahui
2020, 35(7): 1437-1446. doi: 10.13224/j.cnki.jasp.2020.07.011
Abstract PDF(3228KB) icon631 icon555
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The first order linear non-homogeneous differential equation of brush wire wear with respect to time was constructed to explain the wear law of brush seals, and the mathematical model for calculating brush wire wear and wear rate was obtained. The effects of structure and operating condition parameters on wear and wear rate were numerically simulated, and the sensitivity of structure parameters to the influence of brush seal wear characteristics was also analyzed. The results showed that the maximum error between the experimental results and the calculation results of the brush seal considering wear effect leakage amount was 778% by the wear calculation result, proving the rationality of the calculation model. The final wear increased with the increase of brush wire diameter and angle, and the brush wire height and brush ring diameter had no effect on it. The initial wear rate increased with the increase of brush wire diameter and brush ring diameter, and decreased with the increase of brush wire height and brush wire angle. The sensitivity of the structure parameters to the total amount of wear was subject to brush wire diameter, brush wire angle, brush wire height and brush ring diameter.
Double-swirler misalignment effect on outlet flow field
HU Jian, ZHENG Tingting, HU Haosheng
2020, 35(7): 1447-1456. doi: 10.13224/j.cnki.jasp.2020.07.012
Abstract PDF(7263KB) icon566 icon644
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The influence of hydrocyclone eccentricity on the outlet flow field was studied by experimental method when the same hydrocyclone was matched with different sizes of outlet limiting region. The results showed that when the ratio of the boundary size (L) to the characteristic size (D) of the hydrocyclone was less than a certain value (L/D=33), there was an attachment point between the jet at the outlet of the hydrocyclone and the wall of the hydrocyclone. The outlet flow field changed from contraction type to expansion type; for the contractile flow field, the eccentricity of the hydrocyclone had a great influence on the outlet flow field, especially the radial velocity field, the minimum value changed from -4 m/s to 1 m/s; while for the expanding outlet flow field, the eccentricity of the hydrocyclone had little effect, for example, the minimum axial velocity was around -44 m/s, and the minimum radial velocity was -1 m/s. In order to reduce the influence of hydrocyclone eccentricity, the outlet flow field can be expanded by increasing the combined swirl number and reducing the ratio of the outlet limiting region to the characteristic dimension of the hydrocyclone.
Ignition characteristics in evaporating Z-shaped pilot flame-holder
MIAO Junjie, FAN Yuxin, WU Weiqiu
2020, 35(7): 1457-1465. doi: 10.13224/j.cnki.jasp.2020.07.013
Abstract PDF(3998KB) icon563 icon453
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The ignition characteristics in an evaporating Z-shaped flame-holder were experimentally studied. The kernel formation and flamelet growth at various ignition positions were acquired using high-speed photography and image processing, and the droplet size and distribution in addition to the time-averaged flame structure in the recirculation zone were analyzed. The experimental results showed that, compared with the traditional film evaporation flameholder, the evaporating Z-shaped flameholder can decrease the lean ignition and blowout equivalence ratios by 311% and 194% when Mach number was over 02. The formation of the initial kernel was related to the ignition position, caused by the double-reaction-zone morphology in the Z-shaped evaporating flame-holder. When the kernel generation was more contributed by the second reaction zone, the ignition performance of the Z-shaped evaporating flame-holder was better and the flamelet growth was faster. The ignition capacity was better when the ignition position was near the lower corner of Z-gutter, and got worse when the ignition position moved to the interface of recirculation zone and mainstream; meanwhile, the non-uniformity of oil mist attributed to the low fuel evaporation rate in the evaporation tube under low temperature and high speed conditions caused the transverse difference in lean ignition performance.
Effect of asynchronous ignition phase on performance of four-stroke engine
CUI Huasheng, ZHAO Zhenfeng, LI Binshi
2020, 35(7): 1466-1472. doi: 10.13224/j.cnki.jasp.2020.07.014
Abstract PDF(3117KB) icon428 icon440
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In order to understand the impact of asynchronous ignition phase on the performance of four-stroke aircraft piston engine fueled with aviation kerosene, one CFD model about combustion chamber was established and confirmed. The simulation results showed that: at 5 000 r/min, 30% throttle opening position and 20 mg fuel quantity condition, the spark ignition timing for the spark plug inside the main chamber was fixed at 20° crank angle (CA) before top dead center (BTDC), another ignition timing for the spark plug inside the pre-chamber was set ahead of 4°, 8°and 12° relatively; with the increase of the phase difference for the two spark plugs, the in-cylinder pressure and heat release rate increased, the occurrence of the knocking combustion moved to the top dead center and the concentration of the knock intensity increased gradually as well.
Influence of axial wide of pressure relief chamber on leakage characteristics and hysteresis of brush seals
LI Pengfei, HU Yaping, CHEN Wenyang
2020, 35(7): 1473-1481. doi: 10.13224/j.cnki.jasp.2020.07.015
Abstract PDF(2143KB) icon513 icon431
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The leakage characteristics and hysteresis effect of different axial width of pressure relief chamber of 0, 04 mm and 06 mm with the conventional and low hysteresis brush seals were studied under the static and dynamic tests of pressure difference rise and drop and the rotor speed rise and drop. The results showed that: the dynamic leakage coefficient was about 14%-20% lower than the static one, when the pressure drop was more than 02MPa. The sealing performance of low hysteresis brush seals was better, and the leakage coefficient was up to about 20% lower than the conventional brush seal. The hysteresis effect was the strongest in the process of pressure difference rise and drop cycle with the static condition when axial width of pressure relief chamber was 06 mm. The hysteresis effect of conventional brush seal was the strongest in the process of pressure difference rise and drop cycle with the dynamic condition. After the rotor speed rise and drop cycle, the leakage coefficient decrease by about 15% when the axial width of pressure relief chamber was 06 mm, and there was basically no hysteresis effect when the axial width was 04 mm. In addition, for the three structures, the brush seal with the axial width 04 mm had the best sealing performance and the weakest hysteresis effect.
Splash lubrication simulation analysis and verification of a gearbox based on CFD
LI Yuzhe, AI Yongsheng, LIU Weizhen
2020, 35(7): 1482-1488. doi: 10.13224/j.cnki.jasp.2020.07.016
Abstract PDF(2479KB) icon808 icon482
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In order to evaluate whether the oil storage structure of splash lubricating gearbox was reasonable, a dynamic simulation model for the splash lubrication analysis of gearbox including gearbox housing, spiral bevel gear based on the computational fluid dynamics (CFD) method was established, and the splash lubrication fluid simulation calculation and analysis of gas-liquid two-phase flow were carried out, then the movement track and distribution cloud diagram of lubricating oil in gearbox were obtained. Through the simulation analysis, it was found that the amount of oil collected at input oil pocket was 531 mL, greater than the amount of oil collected at output oil pocket 65 mL, and the No4 oil pocket cant collect lubricating oil, so the design of No4 oil pocket was unreasonable. According to the result of splash lubrication test, it shows that the trend of the simulation analysis result is consistent with the experimental result, which verifys the correctness of the simulation analysis method and provids a guidance for the design of oil storage structure of splash lubricating gearbox.
Transient temperature field of spiral bevel gear in helicopter transmission system under starved lubrication
LI Fei, WANG Sanmin, LI Zhibin
2020, 35(7): 1489-1495. doi: 10.13224/j.cnki.jasp.2020.07.017
Abstract PDF(2504KB) icon537 icon430
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Based on the theory of heat conduction and tribology, the mathematical model of friction heat of meshing tooth surface with the combination of elastohydrodynamic lubrication and boundary lubrication and the calculation method of transient temperature field under the condition of starved lubrication were established. The distribution of transient temperature field and the temperature time curve were given, and the influences of power and rotational speed on transient temperature field were analyzed. Results showed that in the 5 min process of starved lubrication, the maximum temperature of the driving wheel increased by 657 ℃ when the power increased from 866 kW to 2 000 kW, and decreased by 8502 ℃ when the rotating speed increased from 5 000 r/min to 20 000 r/min. The results lay a foundation for the optimal clearance design of spiral bevel gear in helicopter main reducer under the condition of oil-free lubrication.
Effect of rarefied effect on the performance of tilting pad dynamic pressure gas bearings
YAN Zhenlei, WU Lin
2020, 35(7): 1496-1505. doi: 10.13224/j.cnki.jasp.2020.07.018
Abstract PDF(4472KB) icon596 icon440
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Based on the velocity boundary conditions of the continuous model, the first order slip model and the new WU slip model, the slip modified Reynolds equation considering the rarefied effect was established. Combined with the Newtons method and the finite difference method to solve the modified Reynolds equation, the pressure distribution and bearing capacity of each pad of the tilting pad gas bearing considering the rarefaction effect were calculated. The results showed that the greater the eccentricity, the greater the rotation speed, the greater the compression coefficient and the greater the bearing capacity of the tilting pad gas bearing. After considering the rarefied effect, the calculated bearing capacity of the tilting pad dynamic pressure gas bearing significantly decreased, and as the Knudsen number increased, the bearing capacity calculated by the new WU slip model was significantly lower than the first-order slip model.
Aerodynamic performance of compressor rotor and flow analysis at windmilling condition
LI Da, LU Hanan, PAN Tianyu
2020, 35(7): 1506-1520. doi: 10.13224/j.cnki.jasp.2020.07.019
Abstract PDF(7244KB) icon565 icon499
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To explore the evolutions of inner flow structure and aerodynamic losses in a low-aspect ratio compressor rotor operating from compressor condition to highly loaded windmilling condition (turbine condition), a simplified numerical calculation method based on energy transfer between rotor blade and working fluid was employed to capture the critical windmill points at low rotational speeds. Due attention was paid on comparisons of the evolutions of tip leakage loss and the flow separations in the blade passage at the compressor condition, critical windmill point and turbine condition on a speedline. It was found that the rotor operating mass flow for critical windmill point showned a nearly linear variation trend with the increment of rotating speed. At the same time, with the rotor operating from the compressor to turbine condition, the tip leakage flow traveled across the clearance from the suction surface to the pressure surface at turbine conditions and mixed with the low-momentum fluids on the pressure surface, resulting in flow blockages near the casing endwall. In the meanwhile, the tip flow separation switched from suction surface separation to pressure surface separation, and both the intensity and size gradually increased, leading to higher aerodynamic losses. In the hub region, the flow separation was kept on the suction surface and the size of the separation has presented a growth in the radial direction near the trailing edge.
Experiment on inlet flow field of turbocharger centrifugal compressor under pulsating backpressure,
ZHANG Kaiyue, YANG Mingyang, SHU Mengying
2020, 35(7): 1521-1531. doi: 10.13224/j.cnki.jasp.2020.07.020
Abstract PDF(8305KB) icon442 icon448
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To study the inlet flow field distribution of centrifugal compressor under strong pulsating backpressure, an automatic two-dimensional traversing system for unsteady flow field measurement was developed. The unsteady inlet flow field of the centrifugal compressor under different pulsating frequencies and time-averaged mass flow rate was measured by the traversing system with one-dimensional hot-wire anemometer. The results showed that: both circumferential and radial distributions of inlet velocity and flow angle experienced large periodic oscillations due to the pulsating backpressure. The fluctuation of flow angle was significantly higher at tip than that at the hub. The axial velocity in the circumferential angular region upstream the volute tongue was significantly lower than that in the downstream, and the distortion intensity further increased with the increase of frequency and time average mass flow rate. The maximum radial flow angle difference occurred at about 85% blade height: the maximum flow angle difference was 8 degrees at low mass flow rate and 12 degrees at high mass flow rate. The study proved the unsteady evolution of the inlet flow field of the centrifugal compressor at the conditions of pulsating backpressure, giving the experimental foundation for the theory of the optimal design of the compressor.
Influence of combustion performance of swirl on solid fuel ramjet about carbon black
TANG Changjun, CHEN Guoguang, CHEN Xiong
2020, 35(7): 1532-1540. doi: 10.13224/j.cnki.jasp.2020.07.021
Abstract PDF(3155KB) icon670 icon390
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In order to study the influence of swirl flow and carbon black added propellant on the combustion performance of solid fuel ramjet, pure polyethylene and carbon black added polyethylene were used as solid fuel, and experiments with combustion were conducted in both swirl-flow and non-swirl-flow of different port diameters of fuel grain. And the working performance parameters were calculated based on the parameters obtained from experiment. The results indicated that compared with pure polyethylene (PE), the addition of 5% carbon black could increase the regression rate, characteristic velocity and thrust. In the working conditions of swirl-flow, the temperature and pressure of afterburning chamber were higher than those of non-swirl-flow, besides, the stability of combustion was also enhanced. Meanwhile, the increase of port diameter of fuel grain enhanced the combustion stability and efficiency of SFRJ, but decreased the regression rate.
Numerical simulation for the second pulse ignition progress in compartment dual-pulse motor
TANG Liang, DENG Kangqing, YU Xiaobo
2020, 35(7): 1541-1548. doi: 10.13224/j.cnki.jasp.2020.07.022
Abstract PDF(2902KB) icon469 icon510
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Based on computational fluid dynamics and ignition theory, the flow field during the second pulse ignition of a dual-pulse solid rocket motor was numerically analyzed, and the test of the second pulse ignition of a dual-pulse solid rocket motor was conducted. Result showed that, before the diaphragm was opened, the position of the high pressure zone in the second pulse chamber moved from the front of the chamber to the partition, the pressure changed little along the radial direction of the chamber but more obviously along the axial direction, the near wall area of the second chamber head and tail was kept in the low temperature. The diaphragm was opened at 6 ms, and the pressure in the second pulse combustion chamber decreased by 05 MPa, the pressure difference at the front and rear ends of the inner hole of the propellant grain fluctuated violently, the temperature at the front end of the inner hole of the propellant grain decreased by 600 K, while the temperature in other areas changed little. After the diaphragm was opened, the downstream hole formed a zonal high temperature zone along the axis of the first pulse chamber, peak pressure appeared in the first chamber head and tail, the pressure of the first chamber reached a steady state at 18 ms, and the temperature of the first chamber reached a steady state at 25 ms. The pressure-time curves of the first and second chambers measured in test were in good agreement with the simulation result, indicating that the simulation method has certain accuracy.
Aero-engine stall/surge airworthiness certification method under the influence of crosswind
LI Zhiping, ZHU Xingyu, ZHANG Peng
2020, 35(7): 1549-1558. doi: 10.13224/j.cnki.jasp.2020.07.023
Abstract PDF(4245KB) icon729 icon515
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Surge and rotating stall in compression system are two types of aerodynamic unstable phenomenons often encountered during the operation of aero-engines. The stall/surge characteristics clauses of China Civil Aviation Regulations (CCAR) 3365 in the regulations were analyzed. And Rotor 67 was taken as the research object, a rapid estimation method of engine surge/stall margin under the influence of crosswinds was established from the perspective of airworthiness approval. The results of this method showed that when the crosswind velocity was 35m/s, the surge margin at take-off decreased by 51%, and the surge margin on landing decreased by 198%.
Small sample fault diagnosis of aeroengine based on RS-CART decision tree
PANG Mengyang, SUO Zhongying, ZHENG Wanze
2020, 35(7): 1559-1568. doi: 10.13224/j.cnki.jasp.2020.07.024
Abstract PDF(1060KB) icon813 icon533
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In view of the over-fitting problems caused by the high dimension of feature attributes of small sample sets and noise data, etc, during the construction of CART (classification and regression tree) classification tree, the rough set (RS) attribute reduction based on mutual information was introduced in the process of CART decision tree algorithm training. The similarity between information entropy and GINI coefficients to characterize the “purity” of the sample set was considered, attribute reduction on historical fault data was performed to reduce the attribute dimensions and optimize the training sets.On this basis,a classification decision tree was constructed and the output rules were visualized.Result showed that,when the improved CART decision tree algorithm was applied to the fault diagnosis of a certain type of aeroengine oil,the extracted rules were highly interpretable and can reduce the influence of redundant attributes and noise on decision.Compared with the common fault diagnosis algorithms,the diagnostic accuracy of the model was improved by about 20%,and AUC (area under curve) value was as high as 92%, enabling to effectively deal with the problem of small sample of high-dimensional discrete aeroengine faults.

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