2018 Vol. 33, No. 1

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Determination of fatigue parameters in total strain life equation and life prediction
2018, 33(1): 1-14. doi: 10.13224/j.cnki.jasp.2018.01.001
Abstract PDF(1996KB) icon1624 icon1087
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Several prediction methods were summarized and evaluated, and the expressions of fatigue strength coefficient, fatigue ductility coefficient, fatigue strength exponent, fatigue ductility exponent were given, then an equation having both good physical and mechanical significance and universal utility was proposed, with which good fatigue life prediction results within a scatter band of 2 for six typical aeroengine materials(TC4(room temperature), TC11(room temperature), TC11(500℃), GH901(300℃), GH901(500℃) and GH4133B(600℃)) were gained; four fatigue parameters acquired from several prediction methods were compared and analyzed, and five forms of true fracture stress were proposed, helping to derive the fatigue strength coefficient accordingly. It was found that the true fracture stress proposed gained more accurate results compared with the test having an error not more than 15%, then a conclusion was made that applying true fracture stress could realize high accuracy in midhigh life prediction.
Vibration test of high speed flexible rotor due to the suddenunbalance
2018, 33(1): 15-23. doi: 10.13224/j.cnki.jasp.2018.01.002
Abstract PDF(1410KB) icon1446 icon879
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A high speed flexible cantilever rotor test rig was established to investigate the vibration response of the turbofan rotor in time domain and frequency domain under the suddenunbalance and the rubimpact caused by blade loss, based on the equivalence principle of structural/mechanical characteristics. The research showed that, suddenunbalance led to significant impact on rotor, the aggravation of the rotors transient response, and flexural resonance of rotor; the rubimpact between rotor and stator resulted in the increase of the critical speed of rotor and the nonlinear vibration with the super harmonic frequencies.
Analysis on inverse kinematics of the three rings supporting and driving axialsymmetric vectoring exhaust nozzle
2018, 33(1): 24-29. doi: 10.13224/j.cnki.jasp.2018.01.003
Abstract PDF(783KB) icon1212 icon705
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The three rings supporting and driving axialsymmetric vectoring exhaust nozzle mechanism was divided into three submodules. Spatial position analysis method, analytic geometry, and coordinate transformation method were applied to analyze the upper, middle and lower modules. A complete inverse kinematics model of axialsymmetric vectoring exhaust nozzle was established by each submodules. The experiment and computer simulation results showed that the mechanics design was reasonable and kinematics modeling was effective, the accuracy of the result was 98%, providing an important reference for the optimization design and control of the three rings supporting and driving axialsymmetric vectoring exhaust nozzles.
Ballistic impact behavior of aeroengine composite casing
2018, 33(1): 30-38. doi: 10.13224/j.cnki.jasp.2018.01.004
Abstract PDF(1009KB) icon1197 icon811
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To obtain the dynamic response, damage and failure modes of fiber reinforced composites used as aeroengine fan containment casing under conditions of fan blade out event, ballistic impact tests were conducted on Kevlar woven fabrics laminates in gas gun employing the rectangular blade projectile. It was concluded that when the thickness of composite target increased by 25%, the energy absorption increased 92%. With the increase of blade projectile initial velocity, the damages of composite target became more severe from the slight dent to transverse and longitudinal cracking coupled with delamination failure. After the impact velocity increased over the ballistic limit, the damage turned to the rectangular hole in the impact surface and fiber rupture, fiber pullout and delamination failure in the exit surface. Under the impact of blade projectile, bulge deformation generated in the local contact area of the composite laminate, which recovered after the projectile perforates or rebounds. The roll angle of blade projectile led to larger influencing area due to the orthotropic characteristic and consequent improvement of impact resistance.
Anomaly detection method based on gas turbine sensor associated network
2018, 33(1): 39-47. doi: 10.13224/j.cnki.jasp.2018.01.005
Abstract PDF(885KB) icon1118 icon646
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The mechanism and characteristics of four typical abnormal forms of gas turbine were analyzed, and the mapping between the different abnormal features and the sensor network characteristics were acquired. On this basis, the abnormal characteristics of sensor network were obtained, and the detection strategy of gas turbine anomaly based on sensor correlation network was proposed. The results of experiments indicated that sensor related network model based on multi source information fusion could filter out the correlation between nodes when the correlation indicator was below the threshold of 037, and achieve steadystate anomaly detection of gas turbine effectively, showing that there was a nonlinear trend of abnormal depression greater than 12% during the speed up; although the correlation between nodes under normal circumstances should be a linear trend, this method could achieve dynamic anomaly detection of gas turbine effectively.
Thermal barrier coating life prediction method for a turbine blade
2018, 33(1): 48-53. doi: 10.13224/j.cnki.jasp.2018.01.006
Abstract PDF(771KB) icon1411 icon824
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Based on the stresslife model developed by NASA and integrated in CoatLife software, the life prediction method of the thermal barrier coating on a turbine blade was investigated. Through the introduction of the oxidation mass gain in the life model, the oxidation dynamic was considered， and the high temperature oxidation effect can be introduced in the life model. Because the fatigue strength coefficient was the function of service time and geometric radius, the arbitrary geometry in real structures and the time dependent deterioration effect could be covered. The calculation results showed that the cycle life and the time life of the coating decreased with the increase of the maximum temperature or fatigue strength coefficient. Based on the design temperature field, the life of a turbine blade coating was predicted. The results showed that the spalling life the coating at the half height of the leading edge was about 336h when the cyclic time was 1h, and this agreed well with the real coating life between 300h and 400h.
A methodology for computing bending and torsion deformation ofceramic cores based on convexhull algorithm
2018, 33(1): 54-61. doi: 10.13224/j.cnki.jasp.2018.01.007
Abstract PDF(840KB) icon907 icon779
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Bending and torsion deformation of ceramic core have a direct impact on the wall thickness accuracy of hollow turbine blade. To overcome the difficulties for determining deformation by extracting or fitting contour lines based on 3D registration of measured point sets and CAD model such as the slow convergence and low efficiency, the bending and torsion degree of ceramic core was proposed and a new algorithm for ceramic core bending degree and torsion degree was studied through the geometric characteristics of ceramic core measurement data based on convexhull algorithm and distanceweighted method. Through corresponding verification experiments the accuracy of proposed method was proved. The results indicated that the accuracy of the calculated torsional and bending deformation was 99.55% and 99.98%, respectively; compared with the twodimensional registration method, the deviation of the torsional and bending deformation was only ±0.01mm and ±0.006°, respectively.
Probabilistic fatigue life model for medium and low cycle fatigue based on plastic strain energy
2018, 33(1): 62-69. doi: 10.13224/j.cnki.jasp.2018.01.008
Abstract PDF(772KB) icon1253 icon754
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The fatigue life of turbine disk may show large scatter duo to the variability of parameters such as material properties, geometrical features, load and some other factors. Taking into full account the influence of factors on the fatigue life, such as stress, strain and stress ratio in the loading and unloading process, a probabilistic fatigue life model based on plastic strain energy was proposed for medium and low cycle fatigue. Besides, the factors commonly used to calculate the scatter of fatigue life, like material property, geometry size and load, the randomness of the cyclic stressstrain curve, were also considered. With the method of quadratic interpolation for stress ratio, the relation of plastic strain energy damage parameter and fatigue life under various stress ratios could be obtained. Using the plastic strain energy probabilistic fatigue life model in conjunction with the response surface method and MonteCarlo method, the probabilistic fatigue life of a simulated bolthole specimen of a turbine disk was analyzed. The results showed that the calculated median fatigue life of the simulated specimen was just 022% less than the median test life, while the fatigue life scatter factor was just 581% less than that of the test result, showing high accuracy of the proposed model for probabilistic fatigue life prediction.
Whole engine efficiency optimization of twostage VNT seriesparallel system for diesel engines
2018, 33(1): 69-76. doi: 10.13224/j.cnki.jasp.2018.01.009
Abstract PDF(1041KB) icon900 icon672
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A twostage turbine seriesparallel system based on VNT(variable nozzle turbine) was proposed to recover waste heat from the diesel engine. The system adopted valves to control the system and accomplish the transformation of the series or parallel working modes. And the system was established under the concept of parallel and series working modes separately, and effective diameter was chosen as the parameter to define the flow capability of the turbine. Besides, the influences of the effective diameters of the twostage turbines on the engine power, the power turbine power and the turbocharger performance were analyzed via GTPower, and the effective diameters of the twostage turbines were matched according to the engine working condition. And the series or parallel working mode was controlled by the maximum value of the whole engine efficiency at the specific working condition of the diesel engine. Results showed that through the proper optimization and combination of the twostage VNT and seriesparallel working mode, the system could recover waste heat effectively and improve the whole engine efficiency by 51% during the back tracking period.
Study on performance parameter correction formulaof GTCP131-9A APU
2018, 33(1): 77-86. doi: 10.13224/j.cnki.jasp.2018.01.010
Abstract PDF(816KB) icon1172 icon752
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Performance parameter (exhaust temperature and fuel flow) correction formula of the GTCP131-9A auxiliary power unit(APU) was studied. A universal method of studying the gas turbine engines comparability was proposed at fist. By using this method, the necessary conditions to make this singlerotor and fixed shaft gas turbine engine similar were three equal, independent similarity criterion numbers, namely, flight Mach number, corrected speed and corrected power; other similarity criterion parameters were the functions of these three similarity criterion numbers. Later, according to the similarity of this engine, by using small deviation method, small deviation correction equations of the additional exhaust resistance, fuel heat value deviation and power deviation existing in the process of engine test were given. Result showed that under the condition that the ratio of the output power to atmosphere pressure was constant, GTCP1319A APUs performance parameter correction formula was the sum of the inlet total temperature polynomial, the correction term of additional exhaust resistance, the correction term of fuel heat variation and the correction term of power variation.
Integration design and analysis for curved conical forebody and threedimensional inward turning inlet
2018, 33(1): 87-96. doi: 10.13224/j.cnki.jasp.2018.01.011
Abstract PDF(1016KB) icon1136 icon822
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By analyzing the aerodynamic characteristics of different angles of attack on conical flow field, and based on the streamlines traced concept, an integrated designed methodology for curved conical forebody and threedimensional inward turning inlet was proposed; besides, the effects of three outline and position parameters on the integrated configuration were theoretically investigated. It was discovered that the effect of the expansion angle of side wall on the inlet mass flow rate coefficient was remarkable, while the effect of the central angle on inlet was mainly reflected on geometric features. Furthermore, the mass flow rate coefficient of the inlet demonstrated a negative correlation with the external compression surface length. Based on the investigation of the flow capture shape, an integrated configuration of the curved conical forebody and threedimensional inward turning inlet was then designed and studied numerically. The results show that, at the design point (incoming Mach number is 60), the mass flow rate coefficient of the inward turning inlet is 093, and the total pressure recovery coefficient is 061. In addition, at offdesign point (incoming Mach number is 50), the mass flow rate coefficient and the total pressure recovery coefficient are 086 and 077, respectively.
Shock wave/boundary layer interactions induced by bump in the Bump inlet
2018, 33(1): 97-107. doi: 10.13224/j.cnki.jasp.2018.01.012
Abstract PDF(1097KB) icon1152 icon734
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In order to study the interactions between the conical shock wave induced by the bump of the Bump inlet and the turbulent boundary layer developed from the fuselage, and also estimate its aerodynamic advantages, the semicone and semirhombic cone of some similarities in flowfield structure with bump were selected as references. The threedimensional flowfields with these three configurations were simulated by numerical methods. Based on this, three bumps with different Mach numbers were designed and the effect of the designed Mach number on the bumps flowfield characteristic was studied. The results showed that when the inviscid shock wave strengths of three configurations were equal, the strength of the vortices induced by semicone was the strongest, followed by the bump, and that induced by the semirhombic cone was the weakest. Although the flowfield induced by the bump was very complex, the flow field behaved in quasiconical similarity manner. Although the semicone had the strongest ability to divert the boundary layer, considering the ability of diverting the boundary layer and the inlet exit distortion on the whole, bump was the best, showing why it was selected as the leading compression ramp for supersonic inlet. In addition, at the design condition, increasing the design Mach number appropriately can improve bumps ability of diverting the boundary layer. However, in case of too high designed Mach number, the ability of diverting the boundary layer could almost keep invariant, but the total pressure loss may increase rapidly.
Investigation of inertial particle separator withnonuniform surface materials
2018, 33(1): 108-115. doi: 10.13224/j.cnki.jasp.2018.01.013
Abstract PDF(920KB) icon935 icon561
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To efficiently improve the separation efficiency of larger particles without altering the geometry, the twophase flowfield within a typical vaneless inertial particle separator was calculated and then carefully studied by using numerical method. Three basic patterns of inertialdominated particle motion were firstly obtained through an indepth study on the particle trajectories. Then, taking advantage of the differences of three typical materials in particle rebound characteristics, namely, 2024 aluminum alloy, 7020 rubber and 45 steel alloy, a novel inertial particle separator was designed on the basis of the profound understanding of particle motion. The results show that the separation efficiency of the AC dust and Cspec. sand can be thus raised by 60% and 137%, respectively.
Aerodynamic performance and flow interaction of the coaxial rigid rotor in hover
2018, 33(1): 116-123. doi: 10.13224/j.cnki.jasp.2018.01.014
Abstract PDF(927KB) icon1227 icon555
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A numerical method based on RANS(Reynoldsaveraged NavierStokes) equations was developed to predict the aerodynamic performance of coaxial rigid rotor in hover. Validation of the method was carried out on the hovering tests for the subsonic and transonic flows. The simulation of rigid rotor XH59A in hover showed that CFD prediction of rotor performance agreeed with the flight test data. Compared with single rotor of the same solidity, coaxial rigid rotor had better performance, along with bigger figure of merit. The performance of the upper rotor decreased less than that of the lower rotor. Reasons were related to the suction effect of the lower rotor on the flow and its location in the downwash flow field of the upper rotor, resulting in the decrease of its effect angle attack. Numerical method indicated that the optimum figure of merit for XH59A was 67%, when the collective pitch angle for both rotors was 14°. Compared with traditional coaxial rotor, the interstage distance of rigid rotor was smaller, leading to a better aerodynamic performance.
Experiment of the effect of nozzle spacing on twinjet screech tones
2018, 33(1): 124-130. doi: 10.13224/j.cnki.jasp.2018.01.015
Abstract PDF(897KB) icon944 icon505
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The near field of the supersonic twinjet noise was measured experimentally with fully expanded Mach number ranging from 110 to 160 and nozzle spacing from 16-32 times of nozzle outlet diameter. The phase difference of the near field screech tones radiated from the two jets was analyzed in detail, and the effect of nozzle spacing on the coupling of the twinjet was explored. The experimental results showed that there were two different patterns for the A mode of twinjet screech tone, ie:symmetric and antisymmetric along the central plane of the two nozzles. In the antisymmetric mode, the intensity of the screech tone in the internozzle region decreased, which was slightly larger than the amplitude of the single jet in the symmetric mode. For the twinjet operating in B mode, the screech tone generated by the two jets were in phase in the internozzle region, which reinforced the oscillation of the twinjet, and the amplitude of the screech tone in the internozzle region can reach to 160dB. The phase difference of the C mode needs further study. Comparing the results with different nozzle spacing, it was found that the coupling was suppressed for the B mode when the nozzle spacing was larger or smaller, while both the amplitude and the dominant Mach number range of the C mode increased with the nozzle spacing.
Prediction theory and validation of shock train in variable section duct
2018, 33(1): 131-136. doi: 10.13224/j.cnki.jasp.2018.01.016
Abstract PDF(799KB) icon811 icon522
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The effect of wall heat transfer and variable section cant be analyzed in the current prediction theory of shock train in the straight pipe. Therefore,theoretical analysis model of shock train considering the effect of wall temperature, boundary layer separation and variable section was developed, and the result was compared with the experimental data. The study showed that this model can quickly calculate the isolator parameters change along the axial direction and the error in predicting the leadingedge of shock train was within 26%. Whats more, the theoretical analysis and numerical simulation of shock train in the varialle section duct were studied, indicating that the difference of analytical and numerical solutions was 11%.
Numerical study on dynamic characteristics of journal bearing considering journal whirling motion
2018, 33(1): 137-146. doi: 10.13224/j.cnki.jasp.2018.01.017
Abstract PDF(1091KB) icon1005 icon577
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The unsteady solution combined with mesh deformation technique was used to establish a solution model of the dynamic characteristics of journal bearing in consideration of whirling frequency and orbit of the journal. On the basis of verifying the accuracy of the solution model, the influences of whirling frequency and eccentricity on the dynamic characteristics of journal bearing were studied when journal whirled with sinusoidal orbit, circular orbit and elliptical orbit. Study results indicate that the radical clearance and oil film pressure change along with the whirling motion of the journal. The smaller radical clearance means the greater oil film pressure. With the sinusoidal whirling orbit of the journal, oil film forces change, and the frequency of the oil film force is the same as whirling displacement of the journal. However, the phase of oil film force lags behind the whirling displacement. The whirling frequency and orbit of the journal greatly influence the dynamic characteristics of journal bearing, so the whirling motion of the journal should be considered. With the increase of eccentricity, the absolute value of the dynamic coefficients increase.
Adaptive timefrequency filtering method based on CPP and S transform and its application in fault diagnosis of rolling bearing
2018, 33(1): 147-155. doi: 10.13224/j.cnki.jasp.2018.01.018
Abstract PDF(1582KB) icon1010 icon560
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Aiming at extracting and separating fault modulation message of rolling bearing under variable rotational speed, an adaptive timefrequency filtering method based on chirplet path pursuit (CPP) and S transform was proposed. In this method, the envelope of vibration signal of a gearbox was obtained by Hilbert demodulation, and the S transform was carried out for the envelope signal so as to get its timefrequency distribution, meanwhile, the CPP algorithm was used to estimate the gear mesh frequency from the vibration signal of a gearbox, then, the shaft rotational speed can be got. According to the shaft rotational speed, each adaptive timefrequency filter was designed. Then the timefrequency filtering was carried out for the timefrequency distribution of envelope signal, and the S inverse transform was used for the filtered results so as to get each fault demodulation signal. Lastly, the order spectrum analysis was carried out for each fault demodulation signal, and the fault of rolling bearing was diagnosed according to the demodulation information in order spectrum. Simulation and application examples indicate that the adaptive timefrequency filtering method can adaptively change the filters center frequency and bandwidth according to the frequency variation characteristics of the rolling bearings fault modulation signal, and also can effectively extract and separate each order demodulation message of rolling bearing, besides, it has better separation effect than the ensemble empirical mode decomposition(EEMD) based order spectrum method.
Approximate analytical solution of the Reynolds equation for clearance flow with pressure difference boundary conditions
2018, 33(1): 156-164. doi: 10.13224/j.cnki.jasp.2018.01.019
Abstract PDF(922KB) icon946 icon598
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In order to obtain the lubricant pressure distribution for clearance seal and finite length journal bearing, the Reynolds equation with pressure difference boundary conditions was solved analytically.Using the method of separation of variables in an additive and a multiplicative form, a set of particular solutions of the Reynolds equation was added in the general solution of the homogenous Reynolds equation,thus a closed form approximate analytical solution for Reynolds equation was presented.The load capacity and attitude angle of clearance seal were calculated according to the approximate analytical solution proposed, the load capacity error compared with the result calculated with finite difference method was less than 5%,and the attitude angle error was less than 3 degree and the computational efficiency increased by hundreds of times.
Test on heat transfer characteristics of high pressure turbine casing with active clearance control system
2018, 33(1): 165-173. doi: 10.13224/j.cnki.jasp.2018.01.020
Abstract PDF(993KB) icon1109 icon734
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Casing test specimen for high pressure turbine（HPT）active clearance control（ACC) system of trim size was designed. Operation of active clearance control system was simulated under high temperature and high pressure to verify the flow characteristics of cooling collector and impingement cooling pipes, and investigate the temperature distribution rules of HPT casing as well as responsive characteristics of casing temperature to cooling airflow. Results showed that the pressure distribution of air supply manifold was very even; for impingement cooling pipes, the pressure rose gradually from inlet to the end, but the pressure became consistent as the area of orifice on the pipe increased; the maximum relative deviation of circumferential temperature distribution of casing were 48% and 58%, for nonoperating and operating ACC system; when the ACC system was working, the temperature for turbine outer casing obviously decreased as cooling airflow increased; during the test, the average temperature for cooled parts on the casing decreased as much as 16%－37% up to expectation. Based on the test data, heat transfer model of HPT casing was validated and modified to be more precise and applicable.
Granulometric technique by photographic methods ofYjet nozzles under back pressure condition
2018, 33(1): 174-181. doi: 10.13224/j.cnki.jasp.2018.01.021
Abstract PDF(1025KB) icon941 icon537
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As its hard to achieve useful data by optical measurement granulometric technique of Yjet nozzle in back pressure condition, a photographic method depending on morphology was put forward to get detailed data of the Sauter mean diameter (SMD). The error among photographic methods and phase Doppler particle analyzer (PDPA) was less than 12%. The experimental results indicated that SMD decreased with air flow rate of 0g/s and increased with air flow rate of 55g/s along with pressure rising and flow rate growing under back pressure condition. SMD almost stayed the same by different flow rates under the same pressure condition with air joining. Finally through tests by simulating real variablecondition process in combustion chamber, it was concluded that SMD under variable pressure condition was almost the same with little air joining in nozzle.
Effect factor of laminar burning characteristics of RP-3 kerosene
2018, 33(1): 182-192. doi: 10.13224/j.cnki.jasp.2018.01.022
Abstract PDF(1300KB) icon1141 icon564
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In order to gain the main effect factors of burning characteristics of RP3 kerosene, the flame propagation characteristics of RP3 kerosene over the initial temperature range of 390-450K, the initial pressure range of 01-07MPa, and the equivalence ratio range of 06-15 were measured in the constant volume combustion bomb. Furthermore, the main effect factors of the flame stability and laminar burning velocity of RP3 kerosene were investigated. The results showed that increasing the initial pressure or decreasing the initial temperature led to a decrease in the unstretched flame propagation velocity and the laminar burning velocity, and an increase in the maximum burning pressure of RP3 kerosene. With the increase of equivalence ratio, the unstretched flame propagation velocity, the laminar burning velocity and the maximum burning pressure increased initially and then decreased gradually. The highest unstretched flame propagation velocity and the laminar burning velocity were measured when the equivalence ratio was 12 and the maximum burning pressure was measured when the equivalence ratio was 10. Furthermore, increasing the equivalence ratio or the initial pressure decreased the Markstein length and the stability of the flame front. However, the effect of the initial temperature on the Markstein length was uncertain.
Influence of turbine test criterion parameters on flow similarity
2018, 33(1): 193-200. doi: 10.13224/j.cnki.jasp.2018.01.023
Abstract PDF(970KB) icon1056 icon550
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Based on a transonic high pressure turbine model, the angle and Mach number radial distribution on the outlet cross-section of each blade taken as the flow similarity evaluation criterion, several normal methods of turbine test dimensionless parameters were compared with the design point to provide some suggestions on the turbine test. Results indicated that, the physical speed relative difference between the methods with/without the specificheat ratio was less than 15%, and the simulation result difference was small enough to be ignored. At the inlet temperature of 450K, the method ensuring specificheat ratio, corrected speed and expansion ratio can obtain the best similarity with the design point; when using the method ensuring corrected speed and expansion ratio and method ensuring corrected speed and corrected power, the Mach number difference at the outlet crosssection of the second blade was most visible and the average of relative difference can reach about 6%. The flow similarity turned better when the inlet temperature was higher, and the method ensuring corrected speed and corrected power was better than method ensuring corrected speed and expansion ratio at the same temperature. If the specificheat ratio cannot be ensured, the inlet temperature should be more than 800K to make the Mach number similarity difference of the every blade less than 25%.
Redesign of axial compressor under multistage environment using inverse method
2018, 33(1): 201-208. doi: 10.13224/j.cnki.jasp.2018.01.024
Abstract PDF(991KB) icon906 icon527
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An inverse method for multistage axial compressor was researched based on the fully threedimensional viscous flow solution. The numerical method used was introduced, and the theory and procedure of inverse design method were described. In order to verify the effectiveness of present method, the initial design results of certain high pressure compressor at rear four stages were simulated and redesigned by using present inverse method. The specific method of tailoring the pressure loading distribution on the blade surfaces under multistage environment was developed based on the analysis of the numerical result. The redesigned result indicated that the whole aerodynamic performance of the fourstage compressor was enhanced after tailoring the pressure loading distribution on multi blade rows reasonably. The adiabatic efficiency of the whole compressor almost remained unchanged, while the pressure ratio was increased by 657% at the design point.
Numerical study on the effect of the linear cascade slotted tailboard void ratio on the passage of transonic gasturbine cascade
2018, 33(1): 209-214. doi: 10.13224/j.cnki.jasp.2018.01.025
Abstract PDF(796KB) icon946 icon487
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Transonic test in linear cascade wind tunnel usually uses a tailboard to improve the linear cascade periodicity. In order to meet the tailboard design requirement, a tailboard with void ratios of 15%,30%,50% was designed and optimized with a numerical method to attenuate such effects. The numerical results indicated that, shock waves stemming from the cascade trailing edges reflected back to the passages at the boundaries disturbing the interior flow and breaking periodicity of cascade passage. A substantial attenuation of such interference was obtained via use of a slotted tailboard downstream the blade trailing edge. Meanwhile, the reflected wave strength was different from the impinging one, and under certain conditions, the reflected wave can become an expansion wave, as a consequence, the pitchwise periodicity had a considerable improvement. The 15% tailboard void ratio significantly improved the periodicity of the cascade flow, reducing the periodicity error by 1643% in related to the 50% void ratio tailboard.
Experiment on effect of free jet length on impinging atomization of gel propellant
2018, 33(1): 215-222. doi: 10.13224/j.cnki.jasp.2018.01.026
Abstract PDF(798KB) icon836 icon480
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In order to study the effect of free jet length on impinging atomization of gel propellant, an impinging atomizer was designed, and gelled kerosene and corresponding waterbased simulant were prepared. Discharge coefficient of the injector and the viscosity and stability of the simulant were measured. Impinging atomization experiments were conducted under different free jet lengths for three jet velocities. Spray behavior of the jet and impinging sheet was observed. The breakup length, droplet distribution and SMD(Sauter mean diameter) were obtained. Relative results indicated that increasing free jet length resulted in great change of spray behavior of impinging sheet when jet velocity was low. But spray behavior nearly kept the same at high jet velocity. For three jet velocities, breakup length located between 45mm and 9mm, and decreased with the free jet length. Droplet distribution was in accordance with RosinRammler relation with a high fitting accuracy. All the evenness indexes were between 3 and 4, and gradually declined with the free jet length implying a reduced evenness of droplet diameter. SMD increased with the free jet length at higher jet velocity. In the case of lower jet velocity, SMD decreased at first and then increased slowly. There is an optimal value for free jet length, and the value equals to 25/3 at present. As a result, when designing an impinging injector, better atomization quality can be reached by applying an optimal free jet length.
Mesoscopic structure modeling and numerical simulation of debonding process of composite solid propellants
2018, 33(1): 223-231. doi: 10.13224/j.cnki.jasp.2018.01.027
Abstract PDF(869KB) icon1213 icon577
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To study the damage evolution law of composite solid propellants, the mesoscopic structure model for HTPB(hydroxylterminated polybutadiene) propellants was established based on the molecular dynamics particle filled algorithm. The adhesive contact method was employed for the adhesion interface between AP(ammonium perchlorate) particle and HTPB matrix, instead of the traditional cohesive element method, and the HookeJeeves optimization algorithm was used to identify the parameters of cohesive zone model of the particles/matrix interface. Then both bilinear cohesive zone model and the selfdefined exponential cohesive zone model were employed to simulate the damage evolution process for the interface of AP particle and HTPB matrix, including the initiation, development, gathering and macroscopic crack. The numerical simulation curves and experimental curves were compared, showing that the exponential cohesive zone model can better describe the debonding process between the AP particles and HTPB matrix under the uniaxial tension loading. Finally, the multistage loading experiment was compared with the simulation curve. It was found that the change trend was consistent and the tolerance was less than 10%, demonstrating the high reliability of mesoscopic model and the interface parameters accuracy.
Effect of cavity on liquid jet penetration in supersonic crossflow
2018, 33(1): 232-238. doi: 10.13224/j.cnki.jasp.2018.01.028
Abstract PDF(836KB) icon1074 icon568
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An experimental investigation on the penetration of cavity upstream liquid jet was conducted with high speed camera. Experiments of plate jet and cavity jet were performed on the different conditions of jet positions and momentum flux ratios to investigate the influence of the cavity on the jet penetration. Results indicated that the jet penetration decreased at the inlet of the cavity and the jet boundary bent to the cavity because of the entrainment of the cavity. Jet penetration increased at the outlet of the cavity due to the shear layer impinging the cavity outlet edge, forming a high pressure field. The decrease of momentum flux ratio led to a strong cavity enterainment. The penetration decreased to the lowest at the cavity front edge when the jet position was 3D(where D is the cavity depth).
Trim and stability analysis of tiltrotor aircraft based on numerical continuation method
2018, 33(1): 239-146. doi: 10.13224/j.cnki.jasp.2018.01.029
Abstract PDF(761KB) icon1178 icon658
Abstract:
The nonlinear flight dynamics model of tiltrotor aircraft was developed by considering the influence of rotor wake on wing, horizontal stabilizer and vertical stabilizer. Taking the tiltrotor XV15 for an instance, by simplifying the hovering model, trim result of hovering was easily calculated. Then, based on the hovering solution, using forward velocity and nacelle conversion angle as continuation parameters, trim calculations of helicopter mode, conversion mode and airplane mode were accomplished by numerical continuation method. Stability was also analyzed based on the trim results. Calculated results showed that, numerical continuation method can calculate the trim solution without being limited by the initial value; the continuation method can calculate the trim solution in the whole conversion envelope and provide a global analysis.
Realtime simulation modeling for integrated inlet and engine system based on normal shock position calculation
2018, 33(1): 247-256. doi: 10.13224/j.cnki.jasp.2018.01.030
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Abstract:
An integrated simulation for mixed compression supersonic inlet and engine system was conducted based on normal shock position calculation. A computation scheme was put forward to separate the inlet model into two parts, which were calculated respectively: the external part of the formula was used to compute the oblique shock to obtain internal inlet boundary conditions, and the internal part modelling by quasi onedimensional CFD was used to simulate the effect of back pressure on the normal shock position. Compared with twodimensional CFD simulation, it was found that this method can shorten the calculation time a lot on the premise of guaranteeing parameter accuracy effectively, resulting in a better realtime simulation ability. Further, the inlet model and engine componentlevel model were integrated to output dynamic coupling effects of these two systems. Finally, some necessary simulations were implemented, showing clearly that the integrated model could accurately emulate the dynamic and static influences between inlet norm shock position and the engine. When turbulence occurred in the incoming flow, the change of the normal shock position can be suppressed by adjusting the nozzle throat area and the compressor guide vane angle rapidly. The reduction of the thrust can be reduced by 50%.

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