2018 Vol. 33, No. 11

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Acoustic excitation response and fatigue life analysis and test verification of thin-walled structure under high temperature environment
2018, 33(11): 2561-2572. doi: 10.13224/j.cnki.jasp.2018.11.001
Abstract PDF(1622KB) icon1150 icon922
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To solve thermal-acoustic fatigue of aero-engine thin-walled structure, the coupled finite element method/boundary element method was used to calculate dynamic response of GH188 thin-walled structures. Based on the theory of Miner liner fatigue accumulative damage, an improved rain-flow counting method and a Morrow mean stress model were adopted to estimate the fatigue life of thin-walled structures. With the use of high temperature travelling wave tube tester, GH188 thin-walled structure high temperature acoustic vibration fatigue test was conducted to obtain modal frequency, stress/strain response and fatigue life results of thin-walled structure under different temperatures and acoustic loads. It was shown in the contrastive analysis of the simulating calculation and test results that numerical simulation had accurate location judging for structural damage positions, all in the rooted positions of structures. The first-order thermal modal frequency was of consistent structures, with errors between 0.49%-2.09%, and X-stress response peaks were centered on fundamental frequency. With the rise of temperature, structure softening and stiffness reduction occurred, and response peak moved to the left; as the prediction level was consistent with the experiment, errors were between 1%-3%, validating the accuracy of thin-walled structure calculation method and model thermal-acoustic response. Structure fatigue life showed a decreasing trend with the increase of temperature and sound pressure level, and the predicted value of fatigue life and the test result were in the same order of magnitude, with the error between 3-3.5 times, satisfying the requirements of engineering level life prediction, and validating the effectiveness of simulation method for predicting thermal-acoustic fatigue life of thin-walled structure.
Denoising method for electrostatic dignal based on sparse decomposition
2018, 33(11): 2573-2584. doi: 10.13224/j.cnki.jasp.2018.11.002
Abstract PDF(1298KB) icon983 icon750
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The principle of engine electrostatic monitoring technology was introduced. The complex noise components and types of electrostatic monitoring signals were analyzed. The shortcomings of classical denoising methods were summarized. For the complex noise filtering problem of electrostatic signals, a denoising method based on sparse decomposition was proposed. The process of denoising method based on sparse decomposition was analyzed. The simulation signal and the electrostatic signal of real test vehicle were taken as the analysis objects, and the denoising analysis was carried out by using the proposed method. Compared with the example verification and the denoising effect of other classical methods, the results show that the electrostatic signal denoising method based on sparse decomposition has high flexibility, and can effectively remove the Gaussian white noise and power frequency interference noise contained in the signal background, and retain the components of the useful pulse signal. It has a good application effect on the complex electrostatic signal denoising.
Vibration energy transmitting mechanism of ring-stiffened casing excited by rotor unbalance
2018, 33(11): 2585-2592. doi: 10.13224/j.cnki.jasp.2018.11.003
Abstract PDF(1371KB) icon1019 icon779
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To analyze how the ring-stiffened casing attenuate the overall vibration of aero-engine, a ring-stiffened casing-supporting-spindle coupling model was established by the finite element method, and the vibration power flow method was applied to analyze the vibration energy transmitting mechanism of ring-stiffened casing under the excitation of rotors unbalance. According to above analysis, following conclusion can be summarized: ①Energy vortexes field derived by the ring-stiffened rib can partly detour and dissipate the vibration energy transmitted through spindle to casing; ②The ring-stiffened rib changed the vibration energy transmitting path and attenuate vibration energy backflow; ③The type of energy transmitting wave changed when the vibration energy was transmitted to the ring-stiffened rib, the flexural wave carrying the most of vibration energy was changed to the longitudinal wave, and made the vibration energy transmit along the circumferential direction of the ring-stiffened rib. This prevented the vibration energy from transmitting to other area of casing along the axial direction. The conclusions can provide references for whole aero-engines structure design and overall vibration attenuation.
Vibration characteristics of titanium wide-chord fan blade
2018, 33(11): 2593-2601. doi: 10.13224/j.cnki.jasp.2018.11.004
Abstract PDF(1092KB) icon1351 icon818
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An analysis of vibration characteristics of a TC4 titanium alloy wide-chord fan blade was conducted with both modal simulation and modal test methods. Modal analysis of a fan blade model was conducted by ANSYS-APDL software. Based on the Campbell diagram and mode shapes of the blade, the bending and torsional modes were identified. Analysis of rotating velocity margin and frequency margin of various speed illustrated that both margins of the first order bending mode were over 20%, satisfying the requirement of resonance margin. Pulse impact method and random excitation method were utilized on the three-axis shake table with scanning vibrometer to analyze the response characteristics of impact and multi-axial excitations. Results showed that low-order bending mode response was high due to circumferential and axial excitations, while high-order torsional and combined mode responses were high due to radial excitations. Blade responses of different excitation points and modes were related to the mode shapes.
Multiaxial notch fatigue life prediction based on stress gradient effect
2018, 33(11): 2602-2610. doi: 10.13224/j.cnki.jasp.2018.11.005
Abstract PDF(840KB) icon1018 icon794
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The projection paths on the π-plane under the newly defined principal coordinate system of several typical tension-torsion loading paths were given. A new multiaxial fatigue damage parameter was proposed based on the projection path on the π-plane. With the non-proportional additional hardening effect being considered, a prediction method of the non-proportional cyclic hardening coefficient was proposed and a new non-proportionality description was defined. Furthermore, a multiaxial effective stress gradient factor was defined by combining the tension stress gradient and the torsion stress gradient of finite element elastic analysis, and a multiaxial notch fatigue life prediction model was developed based on the multiaxial stress gradient effect. The multiaxial notch fatigue test results of GH4165 alloy at 650℃ were used to verify the proposed model. On the basis of analytical study, conclusions can be drawn as follow：(1) the proposed multiaxial fatigue damage parameter is suitable for multiaxial fatigue and uniaxial fatigue with a clearly physical meaning；(2) the equivalent stress gradient factor can be determined only by elastic finite element analysis, which is suitable for practical application；(3) the predicted multiaxial fatigue lives of GH4169 alloy using the proposed model agree better with the experimental results,which are almost within two-time scatter band of the test results.
Analysis of similar dynamic characteristics of vibro-acoustic experiment for elastic cavity
2018, 33(11): 2611-2619. doi: 10.13224/j.cnki.jasp.2018.11.006
Abstract PDF(965KB) icon1052 icon705
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In allusion to the vibro-acoustic experiments of cavity in wind tunnel, taking typical elastic cavity as the research object, dimensional analysis was adopted to establish the similitude relations of structural natural frequencies and dynamics for complete geometric similarity model. Combining the structural finite element theory, the similitude relations of structural natural frequencies and dynamics for incomplete geometric similarity model were established by introducing the complete geometric similarity model as intermediate model. Numerical simulations of natural frequencies and dynamics of scale-down elastic cavity model were carried out. According to the numerical results of scale-down model, the dynamic response results of full-scale model were predicted by the proposed similitude relations. Results showed that the predicted dynamic response curves were in coincidence with the actual numerical results, which verified the feasibility of the proposed similitude relations and also provided a theoretic guidance for structural design and vibro-acoustic experiments of scaled down elastic cavity model with similar dynamics. The analysis method of the established similitude relations can be applied to complex thin-wall structures.
Influence of fuel composition difference on lean blow out
2018, 33(11): 2620-2625. doi: 10.13224/j.cnki.jasp.2018.11.007
Abstract PDF(632KB) icon1054 icon677
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In order to promote the diversification of alternative fuels and expand the compositional distribution of aviation fuels, the single-head combustor was adopted to investigate the effects of diesel oil and high-boiling-point Fischer-Tropsch fuel (FT) on the lean blowout of combustor compared with standard jet fuel. The boundaries of lean blowout (LBO) were researched by changing the pressure at the inlet and outlet of the combustor, and the correlation of LBO with physical and chemical properties as well as compositions was discussed. The results showed thatthe LBO of jet fuel was slightly better than that of the alternative fuelsunder the outlet pressure of 220kPa, whilehigh boiling point Fischer-Tropsch fuels LBO was 5% narrower than that of jet fuels. At the pressure of 140kPa, the LBO of high boiling point Fischer-Tropsch fuel broadened by 8% than that of jet fuel. The analysis shows that low-boiling alkanes and straight-chain alkanes have a better performance in LBO.
Parameteric investigation on ignition overpressure mitigation performance of rocket by water mist
2018, 33(11): 2626-2634. doi: 10.13224/j.cnki.jasp.2018.11.008
Abstract PDF(990KB) icon1020 icon708
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To research the mitigation performance of rocket ignition overpressure by water mist layer, the theory of plane wave propagation in different medium was applied to expore the mechanism for ignition overpressure mitigation by water mist layer. And, main influential factors of ignition overpressure mitigation performance were obtained from theory analysis. Furthermore, the influence rules of the factors on the mitigation performance were studied by numerical computation and the proper value ranges of influential factor under the conditions of rocket safety launching were given. At last, the parameter levels of influential factors for numerical computation cases were arranged by the uniform design. Meanwhile, the parametric model of the influential factors to the mitigation performance was built by regression, and the mitigation efficiency was optimized. The numerical results show that the main influential factors include water droplets diameter, water mist volume fraction and water mist layer thickness. And, there are two different mitigation mechanisms between water droplet and ignition pressure pulse which are closely related to droplet diameter. In addition, there is a parametric model of the influential factors to the mitigation performance when the influential factors falls within some value ranges, and fiducially probability of the model is not less than 95%.
Hydraulic vibration experiment on a rocket engine feed system after pump
2018, 33(11): 2635-2643. doi: 10.13224/j.cnki.jasp.2018.11.009
Abstract PDF(1183KB) icon932 icon725
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The dynamical characteristics of liquid rocket engine propellant feed system after pump have important effect on the stability of thrust chamber. In order to investigate the dynamical characteristics of the propellant feed system after pump in an engine, the hydraulic vibration experiments within the medium and high frequency ranges of the full scale engine feed system after oxidizer pump were conducted. Test data indicate that resonance characteristics of the engine feed system were excited. Under the test condition, the first four resonant frequencies and the vibration modes can be clearly revealed. The first resonant frequency had highest response amplitude, while the second resonant response amplitude was lower than the first one, and similar to the third one. The fourth resonant response amplitude was further lower than the third one. Under the external pressure fluctuation, this engine feed system after pump can easily achieve the resonant condition. When the fluctuation frequency was close to the resonant frequencies of the feed system, the pressure oscillations along the feed system presented obvious resonant wave shapes. The position of the injector manifold is always the wave node of pressure oscillation, namely the wave anti-node of flow oscillation, under different resonant frequencies.
Applicability of empirical formula for flexible joint structural stress
2018, 33(11): 2644-2650. doi: 10.13224/j.cnki.jasp.2018.11.010
Abstract PDF(808KB) icon1034 icon786
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An 8cm pivot radius flexible joint with reinforcement hoop stress measuring system was designed, and the reinforcement hoop stress due to different vessel pressures and vector angles was tested. The results were compared with the empirical formula and finite element analysis. Moreover, the effect of pivot radius on the reinforcement hoop compressive stress was investigated by finite element analysis. New formulas to compute the reinforcement hoop compressive stress for the pivot radius within the 6-10cm were proposed. The effect of throat diameter on the reinforcement hoop compressive stresses of flexible joint was also studied, and the applicability of conversion empirical formula between cold-flow vessel pressure and hot fire motor pressure was discussed. Results showed that a good agreement for the reinforcement hoop compressive stress between test and finite element analysis was obtained. Empirical formulas for reinforcement hoop compressive stresses were not applicable. The flexible joint structural stresses in vessel and the fire test of soild motor rocket were different. The reinforcement hoop compressive stresses for the hot fire test of flexible nozzle can be converted by the joint test in vessel through empirical formula. The elastomer shear stresses were more serious for the joint test in vessel than the fire test of solid motor rocket with flexible nozzle.
Structural reliability simulation and parameter sensitivityanalysis of cooling channel for thrust chamber
2018, 33(11): 2651-2659. doi: 10.13224/j.cnki.jasp.2018.11.011
Abstract PDF(1021KB) icon983 icon713
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In order to evaluate the structural reliability of regenerative cooling channel in thrust chamber body for liquid rocket engine, a structural reliability simulation procedure was established based on finite element thermal-structure coupling calculation. Considering the stochastic influence of engine systems interfering factors, the chambers machining dimension and material performance of the chamber wall, the distribution type of equivalent stress in dangerous points was determined by means of Monte Carlo(MC) simulation and Epps-Pulley(EP) test method. Lower confidence limit of reliability for cooling channel was determined by use of a stress-strength interference model based on the parameter estimation interval, point-low confidence limit method and Lindstrom-Maddens(L-M) method. Then parameter sensitivity was analyzed. Results indicated that dangerous points of inner wall were determined according to the structure reliability simulation, and lower confidence limit of reliability was obtained, making it more practical in engineering. The strength margin of outer wall was much greater than that of inner wall and the structural reliability of cooling channel depended on inner wall. It was an efficient approach to improve structural reliability by enhancing combustion efficiency or selecting inner materials with slightly lower thermal conductivity and higher strength.
Numerical simulation of liquid film cooling for combustion chamber wall of liquid rocket engine
2018, 33(11): 2660-2668. doi: 10.13224/j.cnki.jasp.2018.11.012
Abstract PDF(924KB) icon1005 icon728
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To study the liquid film cooling in liquid rocket engine, a liquid film model was established. The convection heat transfer and radiative heat transfer between the core flow and the liquid film, and the convection heat transfer between the wall and the liquid film were considered to analyze the heat quantity. The mass transfer inducing the entrainment and evaporation of the liquid film was calculated. The friction force between gas-liquid interface and liquid-solid interface was used to analyze the film flow. The model was used in the numerical simulation of flow field within a small engine with 400N thrust. The numerical simulation results were in good agreement with the test data, showing that the model is reasonable and feasible. Comparative analysis of simulation results of different radius and the length of cylinder section of the combustion chamber revealed that within a certain range, with the increase of the radius and the length of the cylinder section, the liquid film length decreased, and the chamber wall temperature increased, so the cooling effect became worse, the result can offer a reference for the liquid rocket engine design.
Numerical simulation of light-craft effects onlaser supported donation wave with gas-liquid two phase propellant
2018, 33(11): 2669-2677. doi: 10.13224/j.cnki.jasp.2018.11.013
Abstract PDF(966KB) icon737 icon489
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The numerical model of impulse laser supported donation wave with gas-liquid two phase propellant was established to analyze the evolution process of the donation wave and flow field, based on the actual light-craft boundary condition. The characteristics and evolution form of temperature, pressure, velocity field change were analyzed. The results showed: the development trend of donation wave was basically identical regardless of the craft at the first 30μs. At the end of laser action, the temperature and pressure reached to the maximum in the focal range. While the velocity kept rising to the maximum and then dropped gradually, the maximum temperature was near the focus, maximum stress occurred at the center and then transferred to the front of the wave, and maximum speed occurred on the shock wave. When combined with craft, the shock wave produced thrust coupled with the wall. The maximum temperature center shifted outward because of the shock wave reflection. The pressure and speed reached the maximum at two sides of the interface where the shock wave edge got to the wall, and then decreased toward the inside gradually.
Pressure loss and heat transfer characteristics experiment of swirling impinging jet with different shape nozzles
2018, 33(11): 2678-2686. doi: 10.13224/j.cnki.jasp.2018.11.014
Abstract PDF(1104KB) icon870 icon560
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A type of swirl nozzle, i.e., a threaded hole nozzle with four spiral grooves on the diameter of the hole was proposed. The heat transfer characteristics of the three kinds of swirl nozzles (insert, built-in torsion belt and guide vane) with the helical hole nozzle at the same helix angle when the Reynolds numbers were 6000,12000 were investigated. The pressure and flow coefficient of the air supply chamber corresponding to each nozzle were analyzed. The experimental results showed that the spiral hole nozzle had a high heat transfer efficiency in the central area of the target surface, and the stagnation Nusselt number was 29.7%-43.3% higher than the other three nozzles. When the jet space was limited (semi-enclosed space), the Nusselt number of dropped down by 40% to 60%, and the built-in plug nozzles had the largest drop. In addition, the four kinds of swirl nozzles had the largest air supply chamber pressure of the built-in plug nozzle, one order of magnitude higher than the smallest screw hole nozzle. The analysis of the pressure loss coefficient showed that the pressure loss coefficient of the nozzle hole was the smallest, only about 1/4 of the built-in plug nozzle, the Reynolds number was doubled, and the pressure loss coefficient of the built-in plug nozzle dropped by 14% on average.
Calculation method for gas temperature from combustor outlet based on gas composition
2018, 33(11): 2687-2693. doi: 10.13224/j.cnki.jasp.2018.11.015
Abstract PDF(627KB) icon1066 icon648
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According to different gas compositions in combustor at different temperatures, two calculation methods for predicting gas temperature by establishing different gas models were proposed. Based on the theory of substance conservation, chemical equilibrium and energy conservation, the equations of temperature calculation were established. According to different expressions of the energy conservation equation, the average specific heat capacity of constant pressure method and the enthalpy value method were given, two mathematical methods for solving nonlinear equations were presented at the same time, including three variables iterative method and Newton method. VB (Visual Basic) was used to compile test program to realize temperature algorithm. The calculation example was enumerated to compare the difference between the two algorithms. The result shows that the difference of gas temperatures obtained by the two methods is greater with the increase of oil gas ratio, the result acquired by the high temperature algorithm considering thermal dissociation is smaller, and the reason is that the molar fraction of the dissociated components in the gas increases with the temperature rise, and the actual heat release decreases, leading to the decrease in gas temperature. Therefore when the gas temperature is higher, the high temperature algorithm is more in line with the actual combustion situation.
Influence of flow outlet surface shape on detonation initiation via shock wave focusing in cavity
2018, 33(11): 2694-2702. doi: 10.13224/j.cnki.jasp.2018.11.016
Abstract PDF(1185KB) icon809 icon510
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To improve two-stage pulse detonation engine's operational reliability, a method of enhancing detonation initiation via shock wave focusing was explored. Numerical simulation was conducted, hydrogen was used as a fuel and air as an oxidizing agent. Influences of 3 outlet surface shapes and various exit areas on shock wave focusing were discussed. Results indicated that vertical outlet surface was helpful to increase the pressure and temperature of shock wave focusing and make it occur ahead of focusing time. Pressure of focusing point increased as exit area decreased. Tilting outlet surface was inferior to vertical outlet surface, pressure and temperature of focusing point increase little. Curved exit surface was not helpful to increase the pressure and temperature of shock wave focusing, and detonation wave was not initiated. Compared with 3 outlet surface shapes, vertical outlet surface was better. Simulation results provided a reference for experiment design.
Influence of equivalence ratio on characteristics of continuously rotating detonation combustor
2018, 33(11): 2703-2713. doi: 10.13224/j.cnki.jasp.2018.11.017
Abstract PDF(1345KB) icon829 icon548
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Based on two-dimensional compressible Euler equation, a series of numerical studies were conducted to investigate the effect of equivalence ratio on continuously rotating detonation combustor (CRDC) using methane-air mixture. The developing process and lean-burn extinction process of detonation wave were researched, and the influence of inlet equivalence ratio on performance parameters was analyzed in detail. Results showed that, after ignition, two collisions happened in the developing progress of CRDC from the unstable state to the relatively stable state. Extinction happened in CRDC without happening of two collisions when the inlet equivalence ratio was too low. With the decrease of inlet equivalence ratio, the detonation wave propagation velocity, axial average velocity, outlet average temperature and outlet average total pressure all showed a downtrend. The fundamental reason for the downtrend of the pressurization ratio was that the decrease of entropy increase difference between the rotating detonation combustion process and the isobaric combustion process resulted in the decrease of the Gibbs free energy increment. The fuel residence time was at sub-millisecond level and the thermal efficiency was kept more than 99%.
Numerical investigation of detonator with shock focusing and flame implosion
2018, 33(11): 2714-2724. doi: 10.13224/j.cnki.jasp.2018.11.018
Abstract PDF(1369KB) icon1023 icon519
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In order to solve the problem of shock wave initiation within a short range, a flame focusing structure with a shock wave focusing flame was designed, and the flow field inside the structure was studied by numerical simulation. Results showed that the acceleration region was an important region for the acceleration of flame instability, and the local energy explosion caused by the energy convergence in the focusing region was the key factor for the acceleration of deflagration to detonation transition. In this region, the vortex induced by the geometrical structure can enhance the focusing and hinder the shock wave back into the accelerating region. The transition region of the detonation wave from the over driving state to the stable detonation state was mainly realized in the stable region.The temperature and pressure fluctuations on the central axis were caused by the focusing action of the focusing cavity, and the temperature and pressure changes of the detonation front were caused by the three wave point motions.
Numerical study on water film flow and sheddingin ice accretion of rotating spinner
2018, 33(11): 2725-2736. doi: 10.13224/j.cnki.jasp.2018.11.019
Abstract PDF(1259KB) icon899 icon561
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In order to simulate ice accretion accurately, a water film shedding model on rotating surface was introduced with the method of work balance analysis based on the current three-dimensional coupled model of ice accretion and thin water film on ice surface. A computational methodology and a criteria of water film shedding were then presented. Water film shedding occurred when the work done by air drag force plus potential energy caused by centrifugal force was greater than adhesive work. When the method to numerical simulation of rotating spinner, the simulation results agreed well with experimental results, indicating the current model was reasonable and computational method was feasible. The effect of rotating speed and air speed on water film shedding and ice shape was also simulated. The results show that the proportion of water film shedding increased with larger rotating speed and air speed. The ice mass decreased 13.4% and 15.8% respectively due to water film shedding, when rotating speed was 3000r/min and 6000r/min.The ice mass decreased 12.2%, 13.4% and 14.2% respectively due to water film shedding, when air speed was 40m/s, 50m/s and 60m/s.
Analysis of vibration performance variation of rolling bearing under fuzzy equivalence relation
2018, 33(11): 2737-2747. doi: 10.13224/j.cnki.jasp.2018.11.020
Abstract PDF(1088KB) icon804 icon490
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In the case of small samples with unknown probability distribution, the fuzzy equivalence relation and bootstrap maximum entropy models were proposed, and the variation process of vibration performance of rolling bearing was analyzed by variation probability. The original data of rolling bearing vibration acceleration was grouped into the samples, and then the intrinsic sample was selected to calculate the fuzzy equivalent coefficients between the samples. The bootstrap maximum entropy model was used to establish the probability density function of each sample, and the variation probability of each sample relative to the intrinsic sample was calculated by the intersection method. The relation curve between the fuzzy equivalent coefficients and variation probabilities was established to realize the monitoring of the variation process. The feasibility and correctness of the proposed model were verified by simulation and experimental cases. Experimental investigation showed that the variation probability curve presented nonlinear upward trend like “deck chair” with the increase of wear diameter, which corresponded to the three stages of rolling bearing wear, namely the initial running stage, the normal performance degradation stage and the performance deterioration stage.
Fatigue reliability of high speed bearing based on genetic algorithm optimized artificial neural network
2018, 33(11): 2748-2755. doi: 10.13224/j.cnki.jasp.2018.11.021
Abstract PDF(771KB) icon920 icon524
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To complete the fatigue reliability analysis of aviation bearing under thermal elastohydrodynamic lubrication (EHL) efficiently and accurately, an artificial intelligent method was proposed. The heat stress from temperature was approximated using quadratic polynomial with intercrossing term and then mapped into the Hertz contact zone. The contact stress model, which included the thermal EHL, was established. Considering the randomness of the thermal EHL, the material properties and fatigue strength correction factors, the probabilistic reliability analysis model was established using artificial neural network (ANN). Genetic algorithm(GA) was employed to search the minimum reliability index and the design point by introducing an adjusting factor in penalty function. Reliability sensitivity analysis was completed based on the advanced first order second moment (AFOSM). Numerical example shows that the established probabilistic reliability analysis model could correctly reflect the effect of thermal EHL on contact fatigue of aviation bearing. Compared with the traditional Monte Carlo method, the proposed method presents a difference in failure probability of 2.0×10-4, a relative error of 23.8% and a relative time consumption of only 0.15%, which means that the proposed method has an excellent global search capability and a highly efficiency.
Fault diagnosis of planetary gearbox based on adaptive parameter variational mode decomposition
2018, 33(11): 2756-2765. doi: 10.13224/j.cnki.jasp.2018.11.022
Abstract PDF(1169KB) icon1786 icon592
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In order to solve the problems of variational mode decomposition, including presetting parameter of mode number and failure liability in signal decomposition under the condition of strong noise, an improved method for determining the number of modal decomposition modes and the center of frequency band based on the extreme point of power spectral density was proposed. The effectiveness of the method was verified by signal simulation analysis. Based on the adaptive parameter variational mode decomposition, a fault diagnosis procedure was applied to diagnose the second level sun gear crack of planetary gearbox test platform. Test results proved that the method can accurately decompose the vibration signal, effectively extract and identify the fault characteristic frequency, and achieve accurate diagnosis of the second-stage sun gear crack fault under the condition of strong background noise and weak fault signal.
Effect of non-axisymmetric endwall on secondary flow in axial fan
2018, 33(11): 2766-2775. doi: 10.13224/j.cnki.jasp.2018.11.023
Abstract PDF(1348KB) icon985 icon497
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Computational results to assess the effectiveness of non-axisymmetric endwall contouring in a low-speed axial fan were presented. The endwall was designed by geometric scaling of a prior optimized endwall. Results showed that the isentropic efficiency and total pressure rise coefficient at 100% design speed increased, and the performance of the contoured endwall (CEW) at near stall condition was better than that at the near choke point. Besides, the CEW got 1.27% isentropic efficiency and 2.97% total pressure rise coefficient increased at peak efficiency point. According to the mechanism of the improvement of CEW, the adverse pressure gradient (APG) had been reduced through the groove configuration near the leading edge of the suction surface. Moreover, there was an optimum depth for the groove configuration of this axial fan, which was equal to about 5.73% chord length at stator hub.
Unsteady flow characteristic of rotor-stator interaction in compressor
2018, 33(11): 2776-2783. doi: 10.13224/j.cnki.jasp.2018.11.024
Abstract PDF(1138KB) icon1130 icon622
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Flow of stationary blade interference with the rotor wake was simulated using the large eddy simulation (LES) method. The coefficient of vorticity was used to reveal the evolution mechanism of rotor wake in the stator passage, and the pressure coefficient gradient was used to discriminate the shock structure and wave source. The flow characteristics of the temporal and spatial structures in the flow field were analyzed by dynamic mode decomposition (DMD). Result showed that three wave sources were found at the trailing edge of the moving blade, the leading edge of the stationary blade and the trailing edge. Multi-peak of the frequency spectrum was found in a stator passage flow field. The first order mode represented the transport of wake in the passageway and corresponded to the flow of rotor blade passing frequency (BPF), its unsteady fluctuation was dominant in the flow field. The second order mode was twice of the rotor blade passing frequency and the spatial scale was half of the first order mode, representing smaller scale disturbances.
Steady state error estimation and modification of a shielded thermocouple
2018, 33(11): 2784-2795. doi: 10.13224/j.cnki.jasp.2018.11.025
Abstract PDF(1194KB) icon858 icon501
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For high accuracy measurement of aero-engine exhaust temperature, a conjugate heat transfer (CHT) numerical simulation method was employed to estimate different sources of steady state errors and their variation characteristics of a typical shielded thermocouple working at different Mach number condition namely 0.2,0.3,0.4,0.5,0.6. The results showed that under the Mach number less than 0.3 working condition, the radiation error took the highest proportion of total error, while at the 0.6 Mach number, the conduction error was the main factor affecting the accuracy of measurement. To improve the measurement accuracy of the shielded thermocouple, the influences of the length to diameter ratio of the wire and inlet to outlet area ratio of the shield on the conduction error and radiation error were separately studied. The results showed that the conduction error can be significantly reduced by reasonably increasing the length to diameter ratio of the wire, and as the decrease of inlet to outlet area ratio, the velocity error increased while radiation error decreased there existed a best value of inlet to outlet area ratio to minimize the overall value of the steady state error. Finally, the length to diameter ratio of the wire equal to 12 and the inlet to outlet area ratio equal to 6 were selected to modify the primary shielded thermocouple. After modification, the overall value of the steady state error was reduced by more than 50% in these 5 working conditions, thus the measurement accuracy of the shielded thermocouple was improved.
Aerodynamic optimization design of mixed exhaust nozzle based on FFD technique
2018, 33(11): 2796-2801. doi: 10.13224/j.cnki.jasp.2018.11.026
Abstract PDF(811KB) icon812 icon487
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As a mixed exhaust nozzle was taken as the research object, the mapping relation between the arbitrary shape deformation volume and a mixed exhaust nozzle sketch was built. Through movement of the control points, synchronously large curvature deformation of the profiles and grid was realized. Whats more, experimental samples were established with application of the optimal Latin hypercube design (OLHD) method. On this basis, as the free form deformation (FFD) and CFD modules were driven by the Isight software, all the sample points were calculated. According to the simulation results, optimum sketch was selected with 0.6% increase of the thrust coefficient and 0.6% reduction of the total pressure loss. Finally, multi-lines and arcs were adopted to parameterize the optimum sketch with no performance degeneration, which can be used in engineering practice.
Parameter correction of gas turbine based on an empirical method
2018, 33(11): 2802-2808. doi: 10.13224/j.cnki.jasp.2018.11.027
Abstract PDF(659KB) icon818 icon452
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In order to correct the gas turbine parameter and eliminate the influence of environmental temperature and pressure when assessing the gas turbine engine performance, an empirical method was proposed. The correction exponents were determined by the slope of regression line to the ambient temperature (or ambient pressure), the average of ambient temperature (or ambient pressure) and the average of target parameter, to correct the target parameter. The test data analyses showed that the proposed empirical correction method can more effectively eliminate the influence of ambient temperature and ambient pressure compared with regular correction method, and the correlation coefficient of empirical corrected performance parameter and the ambient temperature (or ambient pressure) was close to zero. The empirical corrected parameters can reflect the state change trend of gas turbine itself well, making it convenient for performance assessment.
Rotor slipstream effects on aerodynamic performance of tiltrotor aircraft in airplane mode
2018, 33(11): 2809-2816. doi: 10.13224/j.cnki.jasp.2018.11.028
Abstract PDF(939KB) icon940 icon506
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An equivalent actuator disk model was developed by taking into consideration such factors as the blade shape, the number of blade, blade pitch and rotating speed of rotor. This technique modelled the rotor implicitly through time averaged source terms in the equations and two test cases were used to validate the actuator disk model. The three-dimensional flow field around V-22 tiltrotor aircraft in high-speed airplane mode was simulated. The characteristics of the rotor flow field were analysed and the increments of aerodynamic coefficients caused by slipstream were also presented. The results showed that the rotor slipstream altered the pressure distributions on wing surface evidently, which increased the lift coefficients up to 4.6%. Slipstream decreased the drag coefficients about 29% at 0° angle of attack. However, after 4° angle of attack, slipstream increased the drag coefficients and the maximum increment was up to 32%. The variation of the pitching moment coefficient was also 4.6%. Further studies show that rotor slipstream has greater effect on the lower surface of the horizontal tail, while making a small impact on the vertical tail.

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