2016 Vol. 31, No. 3

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Review on the blade loss of aero-engine
MA Yan-hong, LIANG Zhi-chao, WANG Gui-hua, ZHANG Da-yi, HONG Jie
2016, 31(3): 513-526. doi: 10.13224/j.cnki.jasp.2016.03.001
Abstract PDF(1166KB) icon1485 icon555
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Research progress on the blade loss of aero-engine was reviewed in recent years. The mechanical problems related to the blade loss process were outlined. The mechanical mechanism, numerical simulation and the test study of the transient dynamical characteristic and survival ability due to blade loss in the rotor and whole aero-engine structural system were discussed emphatically. The studies involved the load and mechanical behavior, the techniques of modeling and calculation, the test of mechanism and the whole aero-engine. The results show that it's necessary to take the whole aero-engine system as object and consider the load aging characteristic of the complex structural system in severe environment. The structural integrity and reliability can be improved by structural and dynamical design strategy.
Effect of interface debonding on matrix multicracking evolution of fiber-reinfroced ceramic-matrix composites
LI Long-biao
2016, 31(3): 527-538. doi: 10.13224/j.cnki.jasp.2016.03.002
Abstract PDF(770KB) icon1064 icon427
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An analytical methodology was developed to investigate the effect of fiber/matrix interface debonding on matrix multicracking evolution of fiber-reinforced CMCs(ceramic-matrix composites). The Budiansky-Hutchinson-Evans shear-lag model was adopted to analyse the micro-stress field of the damaged composites. The critical matrix strain energy criterion, which presupposes the existence of an ultimate or critical matrix strain energy with matrix, was obtained to simulate the matrix multicracking evolution of CMCs. With the increase of the applied stress, the matrix multicracking and fiber/matrix interface debonding occurred to dissipate the additional energy entered into the composites. The fiber/matrix interface debonded length under matrix multicracking evolution was obtained by treating the interface debonding as a particular crack propagation problem. The conditions for no-debonding and debonding during the evolution of matrix multicracking were discussed in terms of two interfacial properties, i.e., the interface shear stress and interface debonded toughness. When the fiber/matrix interface was bonded, the matrix multicracking evolution was much more intense compared with the interface debonding; when the fiber/matrix interface was debonded, the matrix crack density increased with the increasing of interface shear stress and interface debonded energy. The theoretical results were compared with experimental data of unidirectional SiC/CAS(calcium alumina silicate), SiC/CAS-Ⅱ and SiC/borosilicate composites.
Creep-fatigue life prediction of single crystal turbine blade with the influence of stress relaxation
GAO Jing-yun, ZHANG Cheng-cheng, HOU Nai-xian, REN Yuan, LI Ying, WEN Zhi-xun, YUE Zhu-feng
2016, 31(3): 539-547. doi: 10.13224/j.cnki.jasp.2016.03.003
Abstract PDF(849KB) icon1681 icon498
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The creep-fatigue life prediction method for the single crystal turbine blade of commercial aircraft engine with the influence of stress relaxation was established. Based on the thermal-elastic-creep finite element method analysis, the uniaxial iso-strain relaxation model with the multiaxiality adjustment factor was used to simulate the stress relaxation history in whole life. The stress-low-limit was set to the primary stress. The creep strain was modeled with the combined time hardening implicit creep equation. The fatigue damage was calculated by using damage-based rainflow counting algorithms and Morrow equation. The time-divided linear damage cumulative hypothesis based on Robinson rule was used to calculate the creep damage in whole life. The creep-fatigue life was predicted when the total damage reached the critical damage, which was set to 0.5 based on the creep-fatigue data of the single crystal material. Finally the creep-fatigue life calculated considering the stress relaxation is 45.6 times of the life without the stress relaxation. To predict the blade life with both the reliability and economy, the finite element method analysis could be performed in n cycles and then the stress history in 2n cycles could be predicted by using the method established hereto.
Sound absorption characteristics of resonator with multi slits under high sound pressure level
XU Jun, LI Xiao-dong
2016, 31(3): 548-554. doi: 10.13224/j.cnki.jasp.2016.03.004
Abstract PDF(813KB) icon1149 icon475
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For better understanding of the sound absorption mechanism of resonator with multi slits under high incident sound pressure level(SPL), direct numerical simulation(DNS) using low dispersion and low dissipation computational aeroacoustics(CAA) method was carried out to deal with 2-D resonator with multi slits. Good agreement was first found in validation of standard resonator with single slit through comparison. Then the same numerical methods were applied in numerical simulation of multi slits resonators with the same perforation ratio. Results show that under high SPL, vortex shedding contributes dominantly to the sound absorption coefficient, over 68% in each incident frequency. Multi slits could enhance the viscous dissipation of acoustic energy while vortex shedding was suppressed in low frequencies and strengthened in high frequencies, resulting in better sound absorption capability of resonator with multi slits in relatively higher incident frequencies, but with weak influence on low incident frequencies.
Model updating in structural dynamics based on radial-Tchebichef moments
JIANG Dan-dan, ZANG Chao-ping, MEI Qing, LU Yan-hui
2016, 31(3): 555-566. doi: 10.13224/j.cnki.jasp.2016.03.005
Abstract PDF(1302KB) icon1276 icon548
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Vibration mode shape description and model updating method based on radial-Tchebichef moments was proposed and applied to an actual structure. Radial-Tchebichef moments descriptors were extracted from vibration mode data to describe the most important information of the vibration mode data, realizing the process of data compression. Using radial-Tchebichef moments descriptors in correlation analysis, it overcame the difficulty of double mode when the modal assurance criterion was used to describe the symmetrical structure. It also avoided the problems when vibration mode data was used directly in the process of model updating such as large amount of data and misconvergence of updating parameter. Taking the cover of an aero-engine test rig as an example, the virbation modal test was carried out and radial-Tchebichef moments were used in correlation analysis and model updating. The result shows that the frequency deviation between the test and finite element model is reduced from 17.13% to 1.23% after model updating in the first 13 modes and this case verifies the effectiveness of the proposed method.
Analysis of crack propagation for a compressor disk with cracks on pin holes
ZHANG Zhi-xuan, SHI Duo-qi, YANG Xiao-guang
2016, 31(3): 567-574. doi: 10.13224/j.cnki.jasp.2016.03.006
Abstract PDF(1080KB) icon1253 icon480
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Based on the 3-D crack propagation analysis software named FRANC3D V6.0 and a finite element software, a finite element model of fracture mechanics was established by means of sub-model technique. The crack propagation of center hole of rotating plate was simulated. Little deviation of the computing results with the manual solution indicated the feasibility and accuracy of the method. The model was developed to predict the propagation life of disk containing cracks on the pin holes. The 3-D dynamic crack propagation of the model was simulated. The stress intensity factors and the propagation life of the disk were calculated. The analysis method is feasible. The most dangerous crack is on the surface of the pin hole of the disk.
Influence of compression ratio on microstructure and mechanical behavior of metal rubber
GAO Di, MA Yan-hong, HONG Jie
2016, 31(3): 575-580. doi: 10.13224/j.cnki.jasp.2016.03.007
Abstract PDF(805KB) icon1058 icon453
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Metal rubber specimens of the same size and mass were manufactured separately with different roughcast heights, and the compression ratio was defined as the ratio of the roughcast height to the metal rubber height. So these different compression ratio specimens were analyzed and then subjected to compression loading in quasi-static regime. The results exhibited that the compression ratio significantly influenced the metal rubber apparent structure and the anisotropy properties along molding and non-molding directions. When the compression ratio was 5 to 6, there were more vertical stacking helix wires in the metal rubber specimens, with a relative small stiffness along the molding direction. When the compression ratio was about 2, the metal rubber specimens exhibited a much bigger stiffness along the molding direction, but an obvious smaller stiffness along the non-molding direction than other specimens. These results indicated that the compression ratio was an important impact factor for the metal rubber behavior and should be well considered during manufacturing and design process.
Coupled simulation of gas radiation and wall temperature in vectored nozzle
LIAO Hua-lin, CHEN Xu-yi, ZHANG Xiao-ying
2016, 31(3): 581-587. doi: 10.13224/j.cnki.jasp.2016.03.008
Abstract PDF(823KB) icon1228 icon489
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Models of heat shield and inner, outer shells were built for investigation.A coupled simulation method of gas radiation and nozzle wall temperature was established based on neat radiation in an enclosure model and heat balance model of wall.Gas radiation in 1~5μm was computed with narrow band model, which was considered transparent in all other bands.A coupled equation of neat radiative heat flux-effective radiosity-wall temperature was developed, and the Newton Rafael method was used to solve the heat balance equation to obtain wall temperature of nozzle.An axisymmetric vectored nozzle with 20°deflection angle was taken for investigation.The infrared spectral radiation and neat radiative heat flux on the nozzle wall and the wall temperature were computed.For verification of the computation method, the neat radiative heat flux for one axisymmetric nozzle of a liquid rocket motor were computed, showing well agreement through comparison. This study also shows that radiative heat flux and temperature in deflected section of axisymmetric vectored nozzle varies remarkably along the circumferential direction, much lower on the deflecting side than the other side.Wall temperature of deflecting side is about 90% of the other side, while the radiative heat flux is only 50%.
Experiment on non-self-similar of Mach reflection of gaseous detonation wave
LIU Jie, ZHAO Huan-juan, DU Zhong-hua, CHEN Xi
2016, 31(3): 588-597. doi: 10.13224/j.cnki.jasp.2016.03.009
Abstract PDF(1039KB) icon1183 icon457
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In order to study the non-self-similarity of Mach reflection of detonation waves, Mach reflection of detonation waves was investigated in a thin rectangular channel, and the schlieren system and smoked foils were used respectively to obtain experimental results about Mach reflection that happened in three kinds of pre-mixtures. The results illustrate that for stable or unstable mixtures, the triple point trajectory rendered by Mach reflection is a curve, which means that the Mach reflection of detonations waves along the wedge doesn't have the characteristic of self-similarity as that of the non-reactive shocks.A crucial feature about the non-self-similarity is found that the trajectory of Mach reflection in detonation waves roughly follows triple point trajectory of non-reactive shock theory at beginning of wedge, and then falls on a line parallel to triple point trajectory of reactive shock theory.When the initial pressure was 10kPa and the wedge angle was 30°, the height of Mach triple point of the pre-mixtures for the transition was 0.8, 1.05cm and 0.5cm respectively, which demonstrates that the transition of unstable mixture happens early than stable mixture.
Effects of combustor length on solid fuel scramjet combustor performance
TAO Huan, WEI Zhi-jun, CHI Hong-wei, SUN Wei-wei, WANG Ning-fei
2016, 31(3): 598-607. doi: 10.13224/j.cnki.jasp.2016.03.010
Abstract PDF(851KB) icon1259 icon464
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Based on foreign researchers' experimental data about solid fuel scramjet's, the numerical simulations concerning about the characteristics of the flow field in the solid fuel scramjet and the combustor performance were described by changing the length of the cylindrical section and the length of the diverging section respectively. A second-order-upwind difference scheme and the pressure-based solver were used for simulating the dynamic flow associated with an axis symmetric physical model. The combustion model in the numerical simulations was finite-rate/eddy-dissipation and the turbulence model was the shear stress transport(SST) k-ω model. The boundary of polymethyl methacrylate(PMMA) solid fuel was defined by the user-defined function. Results indicate that as the length of the cylindrical section increases, the combustion efficiency at combustor outlet decreases from 72.74% to 66.81%, while the total pressure loss decreases, the thrust in the combustor increases from 85.83N to 108.55N. The variation of the length of diverging section makes rarely difference on the flowfield characteristics of the combustor, as the length of the diverging section increases, both the combustion efficiency at combustor outlet and the thrust in the combustor slightly decrease. In the design range of combustor length, if the length of the combustor needs to be increased, it's better to increase the length of the cylindrical section rather than the length of the diverging section.
Influence of air split of a radial swirler on ignition and extinction characteristics
DAI Wei, LIN Yu-zhen, XU Quan-hong, ZHANG Chi, GONG Jing
2016, 31(3): 608-615. doi: 10.13224/j.cnki.jasp.2016.03.011
Abstract PDF(856KB) icon1150 icon464
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The air split of the second stage of the radial swirler was taken as the main design parameter for the ignition and extinction characteristics. Test study showed that the fuel in the chamber, atomized by the co-rotating swirler cup with strong swirl number, has been basically atomized at ignition and lean blow-out conditions of atmospheric pressure and room temperature as a stable fuel atomized at the air-fuel-ratio greater than 3. The droplet had sufficient secondary atomization when the air split ratio of the primary and the second stage of swirlers changed from 0.8 to 1.2, making the swirl cup droplet Weber number greater than 40. Therefore, increase of the second stage of swirler air split will not further improve the atomization quality, there is no influence on the ignition and extinction characteristics.
Micro bubble nucleation inside suspended droplet in combustion
LU Qi-zhi, GONG Jing-song, PIAO Ying, YIN Ya-jun, LI Hui, FAN Hong-yu
2016, 31(3): 616-622. doi: 10.13224/j.cnki.jasp.2016.03.012
Abstract PDF(773KB) icon1223 icon535
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High-speed microscopic camera technology was utilized to observe and research the micro-scale suspend droplet combustion process of aviation kerosene RP-3. The basic mechanism of micro bubble nucleation inside droplet and manifestation were analyzed. Under convex curvature induced nucleation mechanism at low pressure, three forms of nucleation which were confirms were including:(1) Nucleation in the interface of the suspended silk/droplet. The temperature of suspended silk was higher than the droplet temperature on interface, and temperature difference induced the evaporation effect to form the micro bubbles nucleation.(2) Nucleation in the interface of the particles/droplet. Several micrometer range filiform or globular impurity particles or colloid particles inside droplet that form convex curvature side to induce meiobar, in which burgeon bubbles nucleation points.(3) Nucleation on pits of droplet surface. Heavy components form the raft structure and the line tension and surface tension of the droplet surface side simultaneous effect cause indent of the droplet surface, which sprout bubbles nucleation points in the convex curvature side of the pit.These developments laid the foundation for further research on micro-scale combustion.
Analysis on combustion instability based on empirical mode decomposition
FU Yu, GUO Zhi-hui, YANG Fu-jiang, CHE Jun-long
2016, 31(3): 623-630. doi: 10.13224/j.cnki.jasp.2016.03.013
Abstract PDF(942KB) icon1182 icon456
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An experimental study was conducted in the lean-premixed swirl-stabilized combustor at atmospheric pressure and temperature in order to analyze the pressure oscillation in occurrence of the combustion instability. The fluctuating pressure signals exhibited as non-stationary signals. A new method using Hilbert-Huang transform(HHT) based on empirical mode decomposition(EMD) and intrinsic mode function(IMF) reconstruction was investigated. This method was applied to demonstrate the characteristics of pressure oscillations in the lean-premixed combustor when the equivalent ratio was at 0.71 and 0.80. The pulsating signals were decomposed with EMD, and IMF containing specific frequencies was obtained. Through the HHT and statistical analysis, the instantaneous frequency of the IMF was analyzed. The results show that the pressure oscillations display the characteristics of intermittent pulsating, and present the beat at the equivalent ratio of 0.71; whereas at the equivalent of ratio 0.80, the pressure oscillations feature the limit cycle. The validity of this method proves that the IMF reflects the inherent mode when the combustion instability occurs, and it has a strong adaptability.
Numerical study on aerodynamic performance of multi-stage lobed mixer-ejector
CHEN Geng, TAN Xiao-ming, FU Jun, ZHANG Jin-zhou
2016, 31(3): 631-638. doi: 10.13224/j.cnki.jasp.2016.03.014
Abstract PDF(856KB) icon1219 icon459
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Based on three dimensional CFD of single/double-stage lobed mixer-ejector with fixed mixing duct area ratio and length ratio, the effects of fundamental structure parameters on pumping performance were investigated. The results showed that the pumping ratio of double-stage lobed mixer-ejector increased when main stream velocity or lobe diffusion angle rose. The first stage pumping capacity for double-stage lobed mixer-ejector was stronger than single-stage lobed mixer-ejector, meanwhile the total pumping ratio of double-stage lobed mixer-ejector was 100% superior to that of single-stage one. Besides, the maximum vorticity and the velocity circulation became larger with the increase of primary flow velocity. In the direction of main stream, the maximum vorticity of single-stage mixer declined gradually, while the velocity circulation firstly increased and then decreased. However, in the double-stage lobed mixer-ejector, both maximum vorticity and velocity circulation decreased along main stream, with a much higher decreasing speed in the first stage nozzle. What's more, the thermal mixing efficiency declined as primary flow was attached to wall much earlier due to the increase of main stream velocity or lobe diffusion angle. For double-stage lobed mixer-ejector, the thermal mixing efficiency at mixing duct exit section was 6% superior in comparison with single-stage one, though the thermal mixing efficiency of double-stage lobed mixer-ejector rose at a low speed along mixing duct.
Characterization and mechanism analysis of several abnormal aerodynamic phenomena of axial flow compressor experiment
XIANG Hong-hui, HOU Min-jie, GE Ning, LIU Zhi-gang, YANG Rong-fei
2016, 31(3): 639-646. doi: 10.13224/j.cnki.jasp.2016.03.015
Abstract PDF(932KB) icon1146 icon459
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Based on arranging all previous axial flow compressor performance experimental results carried out on a compressor experimental facility, some typical abnormal aerodynamic physical phenomena presented in the experimental system were analyzed. Through analyzing experimental data and validating suppression methods, the formation mechanism of these compressor experimental abnormal aerodynamic phenomena was revealed initially. The research results indicate that the partial inlet guide vanes angle maladjustment produces disturbance on the outlet flow field, and lead to the performance and stability of the compressor deterioration. The inverse flow air occurred at the tip cavity channel of the compressor first rotor is the reason that the measurement value of the out wall static pressure is high before the first rotor. By inhibiting the inverse flow, the compressor aerodynamic performance can improve. The change of corrected mass flow versus the inlet throttling ratio, which is the effective method to determine the leakage problem of compressor experimental intake system. The research results can play an important role on guiding compressor performance experimental fault diagnosis and improving experimental analysis ability.
Influence of blade tip winglet on the off-design performance of a transonic compressor rotor
HAN Shao-bing, ZHONG Jing-jun
2016, 31(3): 647-658. doi: 10.13224/j.cnki.jasp.2016.03.016
Abstract PDF(1407KB) icon1196 icon454
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In order to further reveal the influence mechanism of blade tip winglet on the aerodynamic performance of transonic compressor rotor, a numerical study of aerodynamic performance of transonic compressor rotor with different blade tip winglets was carried out. Base on the analysis of transonic compressor rotor flow instability at different speeds, the mechanism of stability enhancement by blade tip winglet was discussed. It is found that the stall margin of the transonic compressor rotor with the widest pressure-side winglet can be increased by 8.1%, 17.4% and 7.1% at 100%, 80% and 60% design speed conditions respectively. At 100% and 80% design speed conditions, the shock/tip leakage vortex interaction and the blockage zone caused by the tip leakage vortex breakdown are the key factors inducing the flow instability in a transonic compressor rotor. The mechanism of stability enhancement by pressure-side winglet contributes to the reduction of blockage zone caused by the tip leakage vortex breakdown, due to the strength reduction of tip leakage flow and shock/tip leakage vortex interaction. At 60% design speed condition, the large area boundary separation on the rotor blade suction surface plays an essential role to the flow instability inception. Compared with the rotor without tip winglet, the equivalent incidence of the rotor with pressure-side winglet is reduced and the degree of three-dimensional separation on the suction surface is weakened.
Unsteady calculation of pressure pulsations within hydraulic turbine under different entrance sections
SHI Guang-tai, YANG Jun-hu, MIAO Sen-chun, WANG Xiao-hui
2016, 31(3): 659-668. doi: 10.13224/j.cnki.jasp.2016.03.017
Abstract PDF(1751KB) icon1036 icon424
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In order to study effect of different entrance sections on pressure pulsation within hydraulic turbine, a single stage hydraulic turbine was selected, and the internal flow field of hydraulic turbine was calculated and analyzed by software CFX; by setting the monitoring points in each flow components, the pressure pulsation at each monitoring points under different entrance sections was calculated; finally, the calculation results of pressure pulsation were switched by means of fast Fourier transformation(FFT) algorithm, and the distribution of time domain and frequency domain at each monitoring point was analyzed. Result show that with the increase of entrance diameter of volute, the pressure gradually increased at each monitoring point under the larger entrance of volute in the volute, but the pressure gradually decreased at each monitoring point under the smaller entrance of volute. The pressure pulsation was less under the larger entrance of volute when the monitoring points and the shrinkage tube were a greater distance apart, but the pressure pulsation was less under the smaller entrance of volute when the monitoring points and the shrinkage tube were a smaller distance apart. The difference of pressure pulsation of different entrance sections gradually decreased from entrance to outlet at the same time in the impeller. The pressure pulsation of draft tube entrance was maximum under the smaller entrance of volute in the draft tube.
Numerical simulation of single-stage transonic compressor with inlet distortion
GUO Jin, HU Jun, YIN Chao, TU Bao-feng
2016, 31(3): 669-677. doi: 10.13224/j.cnki.jasp.2016.03.018
Abstract PDF(894KB) icon1403 icon449
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A three-dimensional numerical calculation code called CSAC based on body force model was developed and used to predict fan/compressor performance with inlet distortion. First, the modeling method to build body force model was studied. Then, a three-dimensional numerical calculation code was developed. A single-stage transonic compressor flow field with clean inlet was simulated with the code. The calculation results agreed well with the solutions of Reynolds-averaged Navier-Stokes(RANS) and experimental data. The compressor flow field with inlet steady circumferential total pressure distortion and circumferential total temperature distortion were simulated respectively with the code. The results showed that the flow field with inlet distortion in compressor had large scale and strong three-dimensional features, which led to the decrease of compressor total pressure ratio and stability margin. All results show that this model can effectively analyze the effect of inlet distortion on compressor while reducing the dependency on computational resources and engineering experience.
Entropy generation control volume method and its application into flow loss evolution in a compressor with near zero tip clearance
LU Qian, NAN Xi, LIN Feng
2016, 31(3): 678-684. doi: 10.13224/j.cnki.jasp.2016.03.019
Abstract PDF(784KB) icon1094 icon483
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To clarify the variation of the flow structure and the flow loss of the near zero tip clearance, a method for analysis of the entropy generation control volume was presented, which could accurately quantify the local irreversible loss of the flow field at any position. The numerical simulation showed the efficiency was at high level when the tip clearance was within 0.4% span(called near zero tip clearance), and there was an optimal non zero tip clearance where efficiency reached maximum. Entropy generation control volume analysis showed that the total entropy generation in the passage was consistent with the efficiency when tip clearance changed;the entropy generation varied evidently at 20%-80% chord of rotor tip region, dominating the total entropy generation; with the change of tip clearance, the entropy generation of different flow regions varied differently, primarily owing to the change of the flow structure in the rotor tip region. Furthermore, the flow field structure was studied. When the tip clearance was zero, the wall shear stress was the dominant factor of the loss; when the clearance was optimal, the flow was uniform, and the loss was minimal.
Simulation analysis on performance of a high speed centrifugal oil-air separator
HAN Jin-zai, CHEN Cong-hui, XU Rang-shu
2016, 31(3): 685-691. doi: 10.13224/j.cnki.jasp.2016.03.020
Abstract PDF(959KB) icon1023 icon429
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The two-phase flow field in the high speed centrifugal oil-air separator of the aero-engine was numerically simulated by the Euler-Lagrange method. Numerical calculation was applied to analyze the influences of speed and mass flow rate on pressure drop and separation efficiency in a high speed centrifugal oil-air separator. The results indicate that the structural improvement of the rotating hollow shaft has obvious influence on reducing pressure drop and increasing separation efficiency.
Direct thrust control of turbofan engines based on unknown input observer
WANG Bin, WANG Xi, KONG Xiang-xing, YANG Bei
2016, 31(3): 692-699. doi: 10.13224/j.cnki.jasp.2016.03.021
Abstract PDF(853KB) icon1175 icon474
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A research on direct thrust control loop design method of a turbofan engine was carried out. Firstly, an onboard model and a thrust estimator of turbofan engines were built based on unknown input observer(UIO) design. Accurate estimation of the entire flight envelope thrust was achieved through decoupling the external disturbance by the UIO observer. Secondly, an integrated dual-loop direct thrust control scheme was proposed. Respectively, its inner loop control was achieved through rotor speed close-loop control scheme, and its outer loop control through engine thrust close-loop control scheme. It is beneficial to realize the independent design of control parameters for each loop. At the end, disturbance rejection and servo tracking ability of the proposed control scheme was successfully validated by simulation. For the engine of different flight working condition points of the direct thrust control, the thrust control error is not more than 0.1%, the speed control deviation is not more than 0.2%.
Robust LPV/PI control for aero-engine based on polynomial sum of squares programming
WU Bin, HUANG Jin-quan, JIANG Rui
2016, 31(3): 700-707. doi: 10.13224/j.cnki.jasp.2016.03.022
Abstract PDF(785KB) icon1193 icon428
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A controller design method based on the model and polynomial sum of squares(SOS) programming was put forward for the conventional PI controller of aero-engine featuring poor adaptability and difficulty to guarantee robustness. Combining the robust stability conditions of transfer function model and the weak duality theorem, the robust stability conditions of linear parameter varying(LPV) model depicted by polynomial were proposed. Using the frequency response method, a family of transfer function models was obtained from non-linear model. And then these transfer functions were used to get LPV model by polynomial fitting method. With the proposed theorem and the LPV model, the controller design problem could be transformed into SOS programming problem, which was solved to obtain the linear parameter varying/proportion integration(LPV/PI) controller. Finally the controller was applied to a turbofan engine model. And step simulation results show that the settling time of this high pressure rotor speed control system is less than 3 seconds, and the steady state error is zero.
A model-based fault tolerant control strategy for turbofan engine
HE Xiao-dong, GUO Ying-qing, DU Xian
2016, 31(3): 708-716. doi: 10.13224/j.cnki.jasp.2016.03.023
Abstract PDF(836KB) icon1267 icon439
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A model-based fault tolerant control strategy for civil turbofan engine was discussed in order to mitigate or eliminate the adverse effect caused by certain faults through adjustments on existing controller. A controlling objective of recovering operability was presented for engines experiencing deterioration in high-pressure compressor and high-pressure turbine. In order to accomplish this objective, a fault accommodation look-up table was established offline, which was formed by optimal adjustments for design points calculated by solving an optimization problem using genetic algorithm. For a general point in the flight envelope, the adjustments were gained through online interpolation among design points. The strategy was validated simple and effective through simulation. Results showed that stall margins of the booster were all recovered to the corresponding levels of the unfaulted engine without exceeding temperature limitations. Stall margins of the fan and high pressure compressor decreased by less than 5% and the thrust by less than 3%.
Numerical simulation on influence of boundary-layer thickness on the cavity aero-acoustic characteristics
ZHANG Qun-feng, YAN Pan-pan, LI Jun
2016, 31(3): 717-725. doi: 10.13224/j.cnki.jasp.2016.03.024
Abstract PDF(875KB) icon1154 icon468
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To analyze the aero-acoustic characteristics in open cavity influenced by inflow boundary-layer thickness, the cavity with length-to-depth ratio of 5.88 was simulated under conditions of different ratios of inflow boundary-layer thickness to cavity depth and inflow Mach number of 2.0, based on detached eddy simulation method; and the features of sound pressure level spectrum were obtained. The results show that increase of inflow boundary-layer thickness leads to enhanced stability in shear layer and decreased the oscillation amplitude stemmed from shear layer instability. This weakens the interaction between large scale vortex and supersonic main flow, causing the decrease in translational kinetic energy and rotation kinetic energy of large scale vortex. Responding to the energy decrease of large scale vortex, the maximum reduction of the sound pressure level inside the cavity is 7.5dB. Meanwhile, the tone frequencies have about 100Hz shift. A new formula with clarified physical meanings of empirical constant has been deduced from the Rossiter formula based on a new hypothesis. And the frequencies shift phenomenon can be illustrated by the new formula.
Analysis on flow field characteristics of lateral jet on slender body
ZHAO Fa-ming, WANG Jiang-feng
2016, 31(3): 726-732. doi: 10.13224/j.cnki.jasp.2016.03.025
Abstract PDF(787KB) icon979 icon397
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Study was carried out for a slender body with rudders, with free stream Mach number of 2.0, attack angle of 0, 10, 20 degrees respectively, and the jet spout located between the×-shape rudders. First of all, numerical simulation and wind tunnel tests were carried out, and consistent radial pressure distribution near jet spout was obtained, verifying the feasibility of numerical simulation method. And then, the characteristics of change with attack angle of the interaction flow field were analyzed on the basis of flow field structure and flow parameters distribution obtained from numerical simulation. At last, influence of jet interaction on amplification factors was examined according to surface pressure distribution of slender body and rudders near jet spout. Results showed that, with increasing angle of attack, shock before jet moved towards jet spout with reduction of separation region, and pressure ratio increased with augmentation of penetration height. Amplification factors were larger than 1.0 and decreased with increasing angle of attack. When jet spout was located between×-shape rudders, jet interaction was beneficial to the enhancement of jet force. Existence of×-shape rudders eased the wraparound effect of jet, leading to favorable interference to the flow field.
Numerical simulation on re-ingestion characteristicsunder landing state for thrust reverser
CHEN Zhu, SHAN Yong, SHEN Xi-gang, ZHANG Jing-zhou, SHAO Wan-ren
2016, 31(3): 733-739. doi: 10.13224/j.cnki.jasp.2016.03.026
Abstract PDF(877KB) icon1204 icon396
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A numerical study was carried out for a cascade thrust reverser of a turbofan engine with high bypass ratio to investigate the influences of the landing Mach number and crosswind speed on the re-ingestion characteristics of the engine and the flow characteristics with the thrust reverser opened. The results showed that:with the increase of the landing Mach number, the level of re-ingestion of the engine inlet decreased, and then disappeared. The value of the characteristic parameter used to evaluate re-ingestion characteristics reached to an allowable value when the critical landing Mach number was 0.08 without the crosswind. When the thrust reverser encountered the crosswind, crosswind changed the flow direction for the thrust reverser flow. It caused the reverser flow to re-ingest into the engine on the crosswind side with the increase of the total temperature distortion on the air inlet. The value of the re-ingestion parameter increased along with the increases of crosswind speed. Therefore, the critical landing Mach number for the safety increased from 0.08 to 0.12 for the cause of crosswind.
Numerical simulation of axial-injection end-burning hybrid rocket motor
LI Xin-tian, LU Xin, LI Yan-cheng, LIU Jun-yi, ZHANG Cheng
2016, 31(3): 740-745. doi: 10.13224/j.cnki.jasp.2016.03.027
Abstract PDF(684KB) icon1011 icon385
Abstract:
Numerical simulations of a axial-injection end-burning hybrid rocket motor were conducted. The combustion mechanism of this kind of hybrid rocket motor was studied. The simulation models of combustion and flow were established in consideration of both gas-solid interfacial coupling and solid fuel pyrolysis. Numerical simulations of motor combustion were carried out. Analysis shows that, two combustion models, end-burning and side-burning, exist in the motor, and the combustion models mainly depend on the oxidizer velocity. The combustion models change when the oxidizer velocity exceeds the transition velocity. Numerical simulation results also validate the existence of the two combustion models under different oxidizer velocities, and the range of transition velocity matches well with the experimental results in reference.
Pipe flow resistance characteristics of test system for low-thrust NTO/MMH rocket engines with high chamber pressure
LIU Lie, WEI Qiang, FANG Zhong-jian, LIANG Guo-zhu, ZHANG Xue-jun
2016, 31(3): 746-755. doi: 10.13224/j.cnki.jasp.2016.03.028
Abstract PDF(744KB) icon1026 icon402
Abstract:
To research the pipe flow resistance characteristics of the low-thrust NTO/MMH(nitrogen tetroxide/methyl hydrazine) rocket engine with high chamber pressure, comparative analysis of pipe flow resistances on the theoretical analysis, cold-flow tests and firing tests were conducted. According to the calculation methods of flow energy loss, the theoretical analysis models of NTO/MMH pipe flow resistance were established. After alcohol-cold-flow tests and low-thrust NTO/MMH rocket engine's firing tests with high chamber pressure, the pipe flow resistance characteristics fitting formulas based on test results were obtained with the least-square method. Compared with the cold-flow test results, when mass flow rates of alcohol were 0.10~0.40kg/s, 0.09~0.36kg/s respectively, the average errors of theoretical flow resistances of NTO/MMH pipes were 5.42% and 3.67%. With the results of firing tests, when mass flow rates of NTO/MMH were 0.39~0.47kg/s, 0.26~0.31kg/s respectively, the average errors of theoretical flow resistances of NTO/MMH pipes were 2.44% and 2.47%, and those based on cold-flow tests of NTO/MMH pipes were 5.74% and 3.46%, but when mass flow rates of NTO were 0.47~0.51kg/s(without 0.47kg/s), the average errors of theoretical flow resistence and cold-flow tests increased to 16.56% and 9.73%. These NTO/MMH flow resistance characteristics acquired from firing tests could be applied in the firing test, providing a necessary support in design of the rocket engine test system in the future.
Mechanical erosion characteristics of carbon-based nozzlein solid rocket motor
CHANG Heng, WANG Yi-bai, LIU Yu, XUE Bin, CAO Xi-wei
2016, 31(3): 756-762. doi: 10.13224/j.cnki.jasp.2016.03.029
Abstract PDF(748KB) icon1457 icon480
Abstract:
Based on two-phase flow theory and empirical formula, a two-dimensional axisymmetric carbon-based nozzle model was established to investigate the mechanical erosion characteristics, with consideration of evaporation and reaction of droplets. Results obtained from computations with distributions of droplets trajectories and mechanical erosion were described for the 15-lb BATES engine nozzle. The effects of Al mass fraction of propellant and chamber pressure on mechanical erosion were investigated. Results show that the calculated result of maximum mechanical erosion rate is 55μm/s, which falls within the range of experimental results. Al/Al2O3 mixed droplet is the main factor of the mechanical erosion, Al droplets cannot hit the nozzle wall due to rapid evaporation and oxidation. The erosion occurs in the nozzle convergent section, with the peak located upstream the throat, while no mechanical erosion exists in throat and expand zone. The increasement of Al mass fraction shows no significant regularity effect on the mechanical erosion rate. The erosion rate has a superlinear relationship with the chamber pressure.
Research on load sharing mechanism of star gear trains for GTF engine
MO Shuai, ZHANG Yi-du, WU Qiong, WANG Fei-ming
2016, 31(3): 763-768. doi: 10.13224/j.cnki.jasp.2016.03.030
Abstract PDF(683KB) icon1058 icon394
Abstract:
In order to reveal the mechanism of loading sharing among star gears of star gear trains in geared turbofan(GTF) engine, a meshing error analysis was conducted on the eccentricity error, gear thickness error, base pitch error, assembly error, and bearing manufacturing error of gear components of the star gear trains respectively, and the floating meshing error resulting from meshing clearance variation caused by the simultaneous floating of sun gear and annular gear was considered. A refined mathematical model of loading sharing coefficient calculation was established in consideration of displacement compatibility, the calculated load sharing coefficient of two condition was 1.0505 and 1.0452, and the characteristic curve of load sharing was obtained, providing a scientific theory evidence for proper tolerance distribution and control in design and process.

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