2022 Vol. 37, No. 2

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Dynamic characteristics of misaligned gear coupling-bearing-rotor system
ZHANG Guoyuan, LIANG Maotan, GUO Jinxing, NIU Xiaozhe
2022, 37(2): 225-234. doi: 10.13224/j.cnki.jasp.20210017
Abstract FullText HTML PDF(4402KB) icon624 icon175
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For meeting the requirement of the simulated operation of a high-speed turbopump in liquid rocket engine，an internal gear coupling was designed as the key component to transfer the motion during the fast start-up stage.The misalignment of the center axis between the turbo rotor and the test rotor had a significant impact on the dynamics performance of the test rotor.The stiffness and damping theoretical model of the internal gear coupling，the model for solving additional forces and moments of the gear coupling under various misalignment conditions，and the dynamic model considering the misalignment factor for double rotor system coupling the gear coupling and the rolling bearing were proposed.The influences of the misalignment parameters on the dynamic performance (critical speed and vibration response) of the test rotor were obtained by numerical solution of the above coupled models，and the model verification was completed by comparing with the literature.The results showed the vibration response error between the proposed model and literature was less than 15%，and shortening the gear coupling length and increasing the center axis alignment can reduce effectively the dynamic response of the rotor system，and had little effect on the critical speed of the double rotor system.The research results provide a theoretical and experimental reference for the design and safe operation of high-speed turbopump.
Analysis of scrapping characteristics and reliability of civil aero engine high pressure turbine blade in dual failure modes
LIU Zheng, XIE Li, ZHANG Jijun, LONG Changjiang, JIANG Kuan
2022, 37(2): 235-240. doi: 10.13224/j.cnki.jasp.20210007
Abstract FullText HTML PDF(2280KB) icon744 icon126
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The scrapping rate of high pressure turbine （HPT） blades varying with cycles since new （CSN） was calculated in the dual failure modes，and the scrapping of HPT blades was observed after engine removal from wings.The relationship between scrapping rate and failure distribution of HPT blades was proposed in accordance with the theory of fatigue damage accumulation so that the failure distribution and life expectation of blades was obtained.Based on the proposal above and a large number of HPT blade maintenance data of a type of civil aero engine，the failure distribution function of HPT blades was fitted with CSN increasing.It was found that the failure of the Stage 1 HPT Blades of this type of aero engine was subject to exponential distribution，and the failure of Stage 2 HPT Blades subject to uncommon exponential-exponential distribution in the current reliability statistics.
Transient vibration suppression of blisk based on optimizing intentional mistuning
OUYANG Luohui, SHANG Hai, BI Qingzhen
2022, 37(2): 241-250. doi: 10.13224/j.cnki.jasp.20210010
Abstract FullText HTML PDF(3905KB) icon396 icon95
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A transient vibration suppression method of blisk based on optimizing intentional mistuning was proposed.First，a reduced order model of the blisk under transient acceleration or deceleration excitation was established，and the amplification factor representing the effect of the mistuning on the transient vibration was obtained.Then，based on the reduced order model，the probability density distribution of the amplification factors under a series of transient excitations was quickly calculated by Monte Carlo simulation.The results showed that the amplification factor was more affected by small level of random mistuning under transient excitations than under stationary excitations in most cases，and was more sensitive to the small level of random mistuning during fast acceleration excitation.Finally，an intelligent optimization method based on genetic algorithm was used to obtain the optimal intentional mistuning.The mean value and standard deviation of the amplification factors under the effect of 1% random mistuning with optimal intentional mistuning were reduced by 25.6% and 85.2%，respectively，compared with those without intentional mistuning.So，the optimized optimal intentional mistuning can effectively suppress the transient acceleration or deceleration vibration and has good robustness.
Analysis of aero-engine vibration response under sudden unbalance
ZHAO Lu, LIAO Mingfu, HONG Liang, LEI Xinliang, LI Ming, WANG Siji, HOU Lizhen, SHAO Zengde
2022, 37(2): 251-262. doi: 10.13224/j.cnki.jasp.20210014
Abstract FullText HTML PDF(5497KB) icon634 icon194
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In order to study the sudden unbalance fault of engine，a low-pressure rotor model of aero-engine was established，and mode check was finished.On this basis，comparison between analysis and test results of the rotor response of test rig under sudden unbalance was conducted.Then analysis model of the rotor-support-case was established，and comparison between analysis and test results was finished.Result showed that，the angular acceleration term and the transient term of the squeeze film damper，which exist during the actual operation of engine，were taken into account when establishing the rotor-support-case model，and the analysis results were in agreement with the test results.The relative error between analysis result and test result of vibration displacement response at sudden unbalance position was 2.1%.After checking the responses of the rotor，the support-case model was established for response analysis，taking the load of rotor parts as the input of the support-case model and considering the characteristics of engine structure.The analysis results were consistent with the test results，with the relative errors between analysis and test results of vibration velocity response near sudden unbalance position no more than 4.7%.The analysis results show the shock characteristics of rotor response after sudden unbalance and the layer attenuation of rotor-support-case response.The calculation method established has good prospect for promotion.
Position rule of turboshaft engine surge based on bench test
YAN Siqi, LI Benwei, WANG Yonghua, ZHANG Yun, ZHOU Pengyu
2022, 37(2): 263-273. doi: 10.13224/j.cnki.jasp.20210085
Abstract FullText HTML PDF(5204KB) icon580 icon113
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In order to investigate the surge position of turboshaft engine，the pressure signals of air inlet，axial compressor tip，axial compressor outlet and centrifugal compressor outlet were collected and analyzed during the bench surge test.Continuous wavelet time-frequency transform was used to extract the characteristics of the pressure signal.The wavelet coefficients were used as the characteristics of the surge signal，and the threshold value was 10% of the maximum value of the wavelet coefficients.The results showed that the axial flow compressor of a turboshaft engine surged earlier than the centrifugal compressor，and the surge was transmitted from the inlet to the centrifugal compressor in the axial direction，and also along the rotor blade rotation in the circumferential direction.When the real-time surge monitoring was carried out for a certain type of engine，the surge can be detected earlier by monitoring the axial compressor than by monitoring the centrifugal compressor.In the subsequent modification design of a certain type of turboshaft engine，the surge margin of the axial compressor can be increased to improve the anti-surge ability of the whole engine.
Analysis and test verification of stiffness and damping characteristics of aviation clamp with cushion
LIU Xuefeng, ZHANG Yuanlin, ZHANG Decong, YU Tao, GAO Peixin
2022, 37(2): 274-282. doi: 10.13224/j.cnki.jasp.20210078
Abstract FullText HTML PDF(4119KB) icon490 icon106
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The stiffness test device of clamp with cushion was developed. The linear stiffness and torsional stiffness of different specifications of clamp were measured respectively. The measured value of clamp stiffness was introduced into the finite element model of clamp pipeline system. The error was about 5% by comparing the numerical calculation of pipeline inherent characteristics with the test results，verifying the accuracy of clamp stiffness parameters. Furthermore，a clamp damping measurement system was built，and the corresponding modal damping ratio was obtained by measuring the dynamic transmissivity of the clamp. The measured value of the clamp damping was introduced into the finite element model of the clamp pipe system. The error between the numerical calculation results and the test results was about 30%，which further verified the effectiveness of the damping measurement method. This method can provide the technical reference for design of the clamp support of aviation complex pipeline system.
Surface roughness flow control mechanism of highly-loaded axial compressor under low Reynolds number conditions
CHENG Hongzhi, WANG Mingyang, ZHOU Chuangxin, ZHAO Shengfeng, LU Xingen, ZHU Junqiang
2022, 37(2): 283-295. doi: 10.13224/j.cnki.jasp.20210134
Abstract FullText HTML PDF(6786KB) icon614 icon115
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Numerical investigations were conducted to investigate the effects of the surface roughness on the aerodynamic performance of a 1.5-stage highly-loaded axial compressor under low Reynolds number conditions.Results showed that the highest aerodynamic performance improvement was achieved at surface roughness 137.8.The maximum increase in total pressure ratio，blocking flow，and peak efficiency was 4.01%，2.24%，and 5.34%，respectively.Detailed analysis showed that，within the entire region of surface roughness magnitudes，the surface roughness covering from leading edge to the 50% axial chord length on the suction surface had a relatively evident advantage to control the separation and transition，and the aerodynamic performance of compressor at low Reynolds number conditions was improved more distinctly.In general，at low Reynolds number，surface roughness can promote the transition，suppress the laminar flow separation，and change the overall magnitudes and distributions of the velocity and the static pressure，which improved the flow field and performance.However，it also deteriorated the incoordination between the subsequent stages，which induced a stronger corner separation in the aft stator，and limited the further improvement of the overall aerodynamic performance of the compressor.
Mechanism of influence of pre-swirl on leakage and rotordynamic characteristics of swirl brake seal
WANG Xiaowei, SUN Dan, ZHAO Huan, MENG Jigang, ZHANG Guochen, ZHOU Min
2022, 37(2): 296-307. doi: 10.13224/j.cnki.jasp.20210018
Abstract FullText HTML PDF(6236KB) icon347 icon62
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The unsteady dynamic mesh method was used to establish a multi-frequency elliptical whirl solving model to obtain the leakage and dynamic characteristics.The leakage and dynamic characteristics of the seal with 20，40 swirl brakes and 40 long swirl brakes in the circumferential direction under different pre-swirl ratios were studied; based on the experimental verification of the accuracy of the numerical model，the changes of the flow field at the seal inlet，the swirl intensity in the seal cavity，the circumferential pressure difference and the flow excitation force were calculated and analyzed，and the influence mechanism of pre-swirl on the leakage and dynamic characteristics of the swirl brake seal was revealed. The results showed that the prominent feature of the swirl brake seal lies in that it can restrain the flow excitation and has little influence on the leakage. 40 long swirl brakes can reduce the leakage by 0.17% compared with the non-swirl brake seal when pre-swirl ratio was 0.75，primarily owing to the fact that the increase of pre-swirl augmented the circumferential flow component，which further aggravated the whirl dissipation phenomenon between the swirl brakes. The increase in the number of swirl brakes was beneficial to the dissipation of flow by swirling flow between the swirl brakes，thus reducing the leakage. Cross stiffness increased with the increase of pre-swirl ratio，and cross stiffness decreased while direct stiffness and effective stiffness increased with the increase of the number and length of swirl brakes under the same pre-swirl ratio. Direct damping and effective damping decreased with the increase of pre-swirl ratio，and increased with the increase of the number and length of swirl brakes. With the increase of pre-swirl ratio，the circumferential pressure difference of the seal cavity increased，the tangential component of the excitation force increased，and the radial component enlarged，which reduced the stability of the rotor.
Mechanism of influence of notch jet-flow on leakage and rotordynamic characteristics of pocket damper seals
GUO Jindao, SUN Dan, ZHAO Huan, XIAO Zhonghui, MENG Jigang, HU Yong
2022, 37(2): 308-319. doi: 10.13224/j.cnki.jasp.20210021
Abstract FullText HTML PDF(6310KB) icon405 icon62
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The unsteady dynamic mesh method was used to establish a multi-frequency elliptical whirl solving model to obtain the leakage and dynamic characteristics of pocket damper seals；based on the accuracy of the numerical model，the influences of different pressure ratio，rotor speed and notch position on leakage characteristics and the dynamic characteristics were studied，the speed and pressure distribution characteristics of different conditions and the notch position were analyzed，so the influence mechanism of notch jet-flow on leakage and dynamic characteristics of the pocket damper seals was revealed.The results showed that: notch jet-flow enhanced the straight-through effect of pocket damper seals，weakened the dissipation of air kinetic energy in the basic chamber，and increased the leakage.When the pressure ratio increased from 2 to 6.9，the leakage increased by 11.75%-12.67%.The notch jet-flow can reduce the cross stiffness of pocket damper seals，increase the direct damping and effective damping，and the effect was more significant when the rotor swirled at low frequency （frequency was less than 120 Hz）; the notch jet-flow can restrain the circumferential flow of the airflow in the downstream chamber，reduce the circumferential pressure difference，reduce the exciting force and improve the stability of the rotor.When the structural parameters of the notch were same，the circumferential second-order dividing point of the seal tooth at the outlet of the basic chamber was the best notch position.At this time，pocket damper seals had the minimum cross stiffness and the largest direct damping and effective damping.
Time-varying meshing stiffness calculation of straight bevel gears based on energy equivalence
CHEN Siyu, TAN Rulong, GUO Xiaodong, ZHANG Weiqing, SHU Ruizhi
2022, 37(2): 320-329. doi: 10.13224/j.cnki.jasp.20210095
Abstract FullText HTML PDF(4456KB) icon462 icon88
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As one of the most important dynamic excitation sources of gear system，gear time-varying meshing stiffness is a key parameter of gear system dynamics model. In view of the problem of calculating the meshing stiffness of straight bevel gears，the variable section tooth profile was divided into several micro-section tooth segments with equal section based on the idea of micro-element. The calculation model of meshing stiffness of micro-section tooth segments was established based on energy equivalent，and the single tooth meshing stiffness was obtained by using integral method. In addition，based on force balance and deformation coordination conditions，a computational model of gear time-varying meshing stiffness was proposed，and the corresponding formula of transmission error was derived according to geometric relations.The finite element analysis was used to verify the calculation method and analyze the error source. The results showed that the calculation accuracy of meshing stiffness of straight bevel gears can be guaranteed within 2% by using this model，and the purpose of quick solution can be achieved.
Research status and development trend of condition monitoring on main-shaft bearings used in aircraft engines
LIU Peng, WANG Liqin, ZHANG Chuanwei, ZHENG Dezhi
2022, 37(2): 330-343. doi: 10.13224/j.cnki.jasp.20210083
Abstract FullText HTML PDF(4717KB) icon1052 icon321
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The main-shaft bearings in aircraft engines generally endure extreme operational conditions，i.e.，high temperature，high speed，heavy load，poor oil and oil cut-off.Fatigue and wear among other failures in the main-shaft bearings significantly influence the reliability of the aircraft engines.Thus，it is essential to monitor the operational status effectively and precisely.The operating condition characteristics，main failure modes and failure mechanisms of the main-shaft bearings were sorted out.Existing main-shaft bearing monitoring technologies were summarized and compared in terms of vibration，lubricating status，sound，acoustic emission，and temperature.The method and technical characteristics of main-shaft bearings condition monitoring based on multi-sensor information fusion were discussed.Result showed that，the influences of the material and structural characteristics on output signals，the micro and wireless sensors，efficient multi-sensor information fusion methods，and data interaction between the physical and the digital model would become the future research direction of main-shaft bearings.
Analysis of dynamic coupling characteristics of high speed angular contact ball bearing-rigid rotor system under different working conditions
CHEN Shijin, WANG Ruixiang, CHEN Xiaoyang, GU Jiaming, LIU Zhaoxia
2022, 37(2): 344-355. doi: 10.13224/j.cnki.jasp.20210082
Abstract FullText HTML PDF(6026KB) icon662 icon142
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According to the established complete dynamic numerical simulation model of high-speed angular contact ball bearing-rigid rotor system，the effect of rotor vibration on the dynamic performance of the system was analyzed，and the effects of axial load and rotating speed on rotor vibration，load distribution and spin-roll ratio in bearing，cage mass center motion wear were also discussed.The results showed that：when the rotor vibration was considered，the ball load at each position of the bearing differed even under the pure axial load，and for the cage mass center motion including the inner ring frequency，its stability became poor.With the increase of axial load，the rotor vibration and bearing slip decreased.However，with the increase of bearing ball load，the wear of inner and outer raceways first decreased and then increased，and the wear was the minimum when the axial load was 4 N.Both the cage stability and wear increased with the increase of axial load.With the increase of the rotating speed，the vibration of the rotor and bearing wear increased，while the stability of the cage first increased and then decreased.Once the rotating speed reached 40 000 r/min，the bearing wear and the cage stability deteriorated sharply.
Research and verification of thermo-acoustic simulation method based on single-sector combustion test
GAO Xianzhi, WANG Xionghui, FENG Xiaoxing, E Yajia, HE Pei
2022, 37(2): 356-365. doi: 10.13224/j.cnki.jasp.20210117
Abstract FullText HTML PDF(3788KB) icon354 icon86
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An in-house developed thermo-acoustic network model was used to study the effects of different test conditions，outlet boundary conditions，and the length of inlet measurement section on the combustion instabilities of single sector combustion test rig，and the results were compared between simulations and tests.The results showed that the thermo-acoustic network model accurately predicted the unstable frequency at different test conditions.The differences between the predicted and test results were within ±10 Hz，and the errors were within 2%.The previous single-sector combustion chamber test showed that combustion oscillation occurred when the inlet measurement section was 0.4 m.Combustion oscillation did not happen when the inlet measurement section was 0.25 m. Numerical simulations showed that the self-excited combustion oscillation can be excited only when the length of the inlet measurement section was between 0.35 m and 0.44 m，which explained the above test results well.
Simulation of water hammer in liquid nitrogen supplying system based on AMESim
ZHANG Wei, SUN Dewen, CHEN Wanhua, GAO Rong, CHEN Jianye, XIE Junlong
2022, 37(2): 366-374. doi: 10.13224/j.cnki.jasp.20210098
Abstract FullText HTML PDF(3580KB) icon518 icon118
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A dynamic model of liquid nitrogen supplying system （LNSS） for a large cryogenic wind tunnel （CWT） was built based on the advanced modeling environment for simulation of engineering systems （AMESim） platform.The accuracy of the model was verified by the experimental data with the mean deviation less than 6.8%.Accordingly，numerical simulation on water hammer was carried out under two working conditions of instantaneously complete close-down and orderly close-down of the nozzles at the end of the LNSS.Numerical results illustrated that the dynamic model can characterize the features of water hammer in the complex LNSS.The peak pressure at water hammer reached 2.98 MPa under the condition of instantaneous close-down of all the nozzles.By contrast, the peak pressure reached maximum with the value of 2.3 MPa at the last close-down when the nozzles were shut down orderly following four steps.Moreover，fast fourier transform （FFT） analysis illustrated that different frequencies existed in the pressure fluctuations during water hammering.However, the frequencies showed inconspicuous distinct under these two working conditions.The simulation results provide a support for the design check and safe operation of the large CWT.
Summary of three-dimensional measurement technology of liquid surface
ZHOU Wenjun, FENG Shiyu, LI Chaoyue, PENG Hao, PAN Jun
2022, 37(2): 375-382. doi: 10.13224/j.cnki.jasp.20210090
Abstract FullText HTML PDF(2944KB) icon394 icon71
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The optical measurement methods used in the three-dimensional reconstruction of liquid level was summarized to use the optical three-dimensional measurement method in the aircraft fuel tank to measure the three-dimensional shape of the liquid level when the fuel tank and fuel sloshed.The basic principles of stereo vision matching method，fringe analysis method，and fringe placement method were mainly introduced，the application scenarios and development status of the three methods in measuring the liquid surface were briefly described，and the advantages and disadvantages of the three methods in different scenes were analyzed.The challenges of liquid surface measurement technology were also summarized，including the relative lack of research on transparent liquid three-dimensional surface measurement，the fact that traditional three-dimensional measurement method can not be used directly，and whether the solution speed can achieve real-time dynamic measurement.It shows that the application of optical 3D measurement technology to aircraft fuel tank level measurement and oil level detection will develop towards a faster，more accurate and intelligent direction.
Semi-analytic solution and verification for large deflection forming of single-jack semi-flexible nozzle based on elliptic integral
YU Chengguo, ZHANG Zhili, LAI Huan, CHEN Wanhua, CHEN Zhenhua, NIE Xutao
2022, 37(2): 383-390. doi: 10.13224/j.cnki.jasp.20210081
Abstract FullText HTML PDF(3062KB) icon367 icon57
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To improve the analysis accuracy and efficiency of single-jack semi-flexible（SJSF） nozzles in transonic and supersonic wind tunnels，a semi-analytical solution method based on ellipse integral for the flexible plate large deflection was developed.Taking the 0.3 m cryogenic wind tunnel SJSF nozzle as the research object，the mechanical model was established.Based on the Euler beam theory，the differential formulas of the flexible plate deflection were derived，and the elliptic integral form was obtained.Based on the program compiled using Maple software，the semi-analytic solution was carried out under Mach number of 1.15 and 1.3 conditions.The deformation contour and structural equivalent stress were obtained.Compared with the finite element method （FEM） results and experimental measurement，it showed that the elliptic integral results were in good agreement with the other two results.The maximum error of the contour coordinates was 0.18‰ and 0.32‰ of the nozzle outlet height size，respectively.The maximum relative error of the equivalent stress was less than 10%，and the elliptic integral solution time was only 11.2% of the FEM.
Effect of aspect ratio and swirl angle on temperature distribution of double serpentine nozzle for turbofan
SUN Peng, ZHOU Li, WANG Zhanxue, SHI Jingwei
2022, 37(2): 391-403. doi: 10.13224/j.cnki.jasp.20210149
Abstract FullText HTML PDF(6074KB) icon426 icon77
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The effects of the aspect ratio and the swirl angle on the temperature distributions of the internal flow and external jet fields of the double serpentine nozzle with real lobed mixer configuration were numerically investigated.The results indicated that，under the action of the bending configuration with the circular-to-rectangular transition，the streamwise vortices induced by the lobed mixer and the tail cone entrained the core flow to impact the nozzle wall，and the “hot streak” was formed at the wall surface of the second S passage and the linear section.Under the constraint of the criterion of completely shielding high temperature components，the tempera-ture of the “hot streak” on the nozzle wall first increased and then decreased as the aspect ratio raised gradually.The value of the temperature peak of the “hot streak” was up to maximum when the aspect ratio was 5.It rose by 1.3% compared with that in the benchmark nozzle model.The plume core region downstream the nozzle exit was shortened effectively with the increment of the aspect ratio.The temperature of the “hot streak” on the nozzle lower wall first decreased and then increased as the swirl angle raised sustainedly.The value of the temperature peak of the “hot streak” was up to minimum when the swirl angle was 10°.It dropped by 15.9% compared with that under the condition of 0° swirl angle.The lateral width of the plume core region downstream the nozzle exit was enlarged notably while its axial length was shortened effectively with the increment of the swirl angle.
Effect and verification of mass injecting pre-compressor cooling on control plan of turbonfan engine
DONG Haibin, SHANG Guojun, GUO Yingqing
2022, 37(2): 404-408. doi: 10.13224/j.cnki.jasp.20210806
Abstract FullText HTML PDF(1860KB) icon466 icon127
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Mass injecting pre-compressor cooling （MIPCC） can change the co-working line of areo-engine，and then influence the operating characteristic of engine.The influence regulation of MIPCC on control plan was grasped by analyzing the effect of the MIPCC on the dual-rotor turbofan engine parts and whole aero-engine，especially on the slip between high and low rotors，and on this basis，through perfecting related control plan and verifying the effectiveness of the control plan by the experiment.Results showed that，the control static error of engine low pressure rotor speed reduced from 2.6% to 0.49%，and the step of low pressure rotor speed from throttle state to intermediate state reduced from 4.92% to 1.46%，therefore the performance and experiment security of the engine was achieved.
Aero-engine on-board adaptive steady-state model base on NN-PSM
XIANG Dewei, ZHENG Qiangang, ZHANG Haibo, CHEN Cheng, FANG Juan
2022, 37(2): 409-423. doi: 10.13224/j.cnki.jasp.20210138
Abstract FullText HTML PDF(7281KB) icon752 icon108
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In order to establish a high-precision，high-real-time aero-engine on-board adaptive steady-state model suitable for large envelopes and multiple states，a on-board adaptive steady-state model based on neural network and propulsion system matrix fusion （NN-PSM） was proposed.Adaptive steady-state modeling method was based on small deviation linearization method to linearize the engine to extract the propulsion system matrix，which was used to characterize output deviation.The engine baseline model was established based on the neural network，and the relationship between the flight conditions and the engine output was mapped，and the neural network used the strong fitting ability to improve the steady-state accuracy of the on-board model.The Kalman filter was designed in real time to improve the adaptive ability of the model.The simulation was carried out under large envelope and variable state flight conditions，and compared with the traditional compact propulsion system model （CPSM） model.The results showed that the average accuracy of the NN-PSM model was within 0.66%，while the average accuracy of the CPSM model was about 2.07%；the time was about one-tenth of the CPSM model，and the amount of data storage was small.
Design of dual-bell nozzles with different extension pressure distributions
LIU Yazhou, LI Ping, CHEN Hongyu, YANG Jianwen, CHEN Yidan
2022, 37(2): 424-432. doi: 10.13224/j.cnki.jasp.20210096
Abstract FullText HTML PDF(3743KB) icon442 icon103
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For dual-bell nozzles with different extension pressure distribution，the method of characteristics was used to design the maximum thrust，constant pressure distribution，and positive gradient pressure distribution's extended contours.Then design methods were verified by simulation，and the operating processes of dual-bell nozzles with different extension pressure distributions were investigated.Results showed that，extended contours with specific pressure distributions could be designed by the maximum thrust and reverse design method with wall pressure known.Modes transition time of dual-bell nozzles with extensions positive gradient pressure distribution was less than engine start-up，but time of models with extensions negative gradient pressure and constant pressure distribution was longer.Compared with the maximum thrust contour，dual-bell nozzles with extension positive gradient pressure distribution had some performance loss.When extension pressure rising value was 0.001 5 time combustion chamber pressure，the average specific impulse dropped by 0.44%.
Impact of ignition charge on ignition process of dual-pulse solid rocket motor
XIA Dingguo, XU Guiyang, WEI Zhijun, ZHANG Weiqi
2022, 37(2): 433-442. doi: 10.13224/j.cnki.jasp.20210131
Abstract FullText HTML PDF(4028KB) icon615 icon70
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In order to find out the impact of ignition charge on ignition process in the second pulse，a model was established.The axisymmetric unsteady Navier-Stokes equation and the standard k-ε turbulence model were used to simulate the second pulse ignition process.Based on that，the impacts of the igniter working duration and ignition gas flow rate on the ignition delay were studied.The results showed that：when the ignition gas flow rate was constant，increasing the igniter working duration can effectively shorten the second pulse ignition delay，and there existed a limit value of the ignition delay，which was defined as the minimum ignition delay.Different ignition gas flow rates corresponded to different minimum ignition delay，and the bigger ignition gas flow rate indicated the smaller minimum ignition delay.The ignition gas flow rate had a negative exponential relationship with the minimum ignition delay.Choosing the free volume as the sum of the first and second pulse free volumes is more reasonable when calculating the second pulse ignition charge.
Calculation method of fuel temperature conforming to requirements of airworthiness certification
ZHANG Ruihua, LIU Weihua, LIU Wenyi
2022, 37(2): 443-448. doi: 10.13224/j.cnki.jasp.20210008
Abstract FullText HTML PDF(2170KB) icon496 icon104
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Based on the requirements of airworthiness certification，the measured fuel temperature change curve of the central wing fuel tank compartment of a certain aircraft under specified working conditions was taken as the input，and the high-order functional expression of the fuel temperature change rule in each stage was obtained by means of MATLAB polynomial piecewise fitting function.The exponential attenuation equation stipulated in the Monte Carlo evaluation model was used to characterize the change law of fuel temperature.The total ambient temperature （TAT） was obtained by the method specified in the evaluation model，and the equilibrium temperature difference and time constant were obtained by the improved genetic algorithm.The equilibrium temperature difference and time constant obtained by the inversion were then input into Monte Carlo evaluation model for calculation，the calculated temperature data and the measured polynomial data were compared.The results showed that both trends were exactly the same，the temperature difference between each moment did not exceed 1.67 K，the mean difference between the calculated value and the measured value of fuel temperature during the entire flight segment was about 0.050 1 K; in the stage with large error value，the value calculated by program was higher than the value measured by flight，which met the relevant requirements of airworthiness standards.The inversion method of time constant and equilibrium temperature difference is scientific and reliable，which can solve the bottleneck problem in airworthiness certification process and can effectively support the smooth development of airworthiness certification of large aircraft.

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