2019 Vol. 34, No. 2

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Topological optimization of piezoelectric materials on the blades for vibration reduction of bladed disks
2019, 34(2): 257-266. doi: 10.13224/j.cnki.jasp.2019.02.001
Abstract PDF(1278KB) icon827 icon511
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A topological optimization procedure of piezoelectric shunting damping for arbitrary full-scale bladed disks was proposed. Based on the fact that the modal electromechanical coupling factor (MEMCF) is the only parameter that affecting the level of modal damping ratios produced by piezoelectric shunting circuit. Further, it showed that MEMCF was related to modal stress field and the geometry of the piezoelectric materials only. Combining with piezoelectric constitutive relation, a linear weighting of stress components was proposed as the criterion to determine the priority of locations for piezoelectric materials. Accordingly, the topological optimization procedure was presented based on the finite element model of bladed disk, where the piezoelectric materials were introduced by modifying the type and material parameters of elements. Solutions for optimization with respect to multiple modal families, polarized direction setting, and electrode connection were also presented. The proposed procedure was applied to an empirical bladed disk. Results show that 12% damping ratio can be achieved for multiple modes using piezoelectric materials with mass of only 10% of the blade.
Nonlinear state equation self-calibration filtering method
2019, 34(2): 267-273. doi: 10.13224/j.cnki.jasp.2019.02.002
Abstract PDF(498KB) icon735 icon452
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In view of the situation that system state equations are influenced by unknown inputs (such as environmental influence, improper selection of models or parameters, and etc.), a nonlinear self-calibration filtering recursive method for state equations with unknown inputs was proposed based on two nonlinear Kalman filtering methods, the self-calibration rank filter (SRF) and the self-calibration unscented Kalman filter (SUKF) were discussed respectively. According to numerous numerical simulation results and engineering applications, by estimating and compensating the unknown inputs in state equations automatically, the proposed algorithm can improve the filtering effect of the system under the influence of unknown inputs, and the estimation accuracy increased by 80% when compared with the unscented Kalman filtering method (UKF). Moreover, the calculation was simple and convenient for engineering applications.
Three-dimensional full-field modal test method for thin-wall casing based on SLDV technique
2019, 34(2): 274-281. doi: 10.13224/j.cnki.jasp.2019.02.003
Abstract PDF(978KB) icon832 icon507
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A modal test method of casing was proposed based on scanning laser Doppler vibrometry (SLDV), and the 3D full-field vibration measurements of thin-wall casing were completed by studying laser Doppler vibrometry (LDV) measurement principle. A 3D laser measurement method for measuring each part of casing independently and a modal splicing technique were established, the data measured by 3D laser was processed and the modal parameters of casing were identified accurately. Modal correlation between SLDV measurement modes and conventional acceleration sensor measurement modes was analyzed. Results showed that normalized cross orthogonality (NCO) values were about 0.9 and the frequencies difference was very small, validating the feasibility and advantage of using the SLDV to measure the 3D full-field vibration of thin-wall casing.
ptimum design of rotor structure layout and its mechanical properties
2019, 34(2): 282-291. doi: 10.13224/j.cnki.jasp.2019.02.004
Abstract PDF(1117KB) icon1174 icon594
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For the structural design of high thrust-mass ratio aero-engine, the method of optimum design of aero-engine rotor structure was put forward. The optimization of the overall structure layout can effectively improve the material utilization efficiency, obtain higher mechanical properties, reduce the structural mass and increase the thrust-mass ratio. The research content of the rotor structure layout was introduced, and the optimum design method of the structure layout was given. The feasibility of the structure layout design method was verified by optimizing the layout of the high load rotor structure system. The numerical results showed that this method can reduce the structural efficiency loss coefficient by 0.335, and the research content was of guiding significance to the initial structure design of the aero-engine rotor system, playing an important role in screening the design scheme of the rotor structure and shortening the design cycle.
Serviceable limits of a crack type foreign object damaged blade considering high cycle fatigue
2019, 34(2): 292-304. doi: 10.13224/j.cnki.jasp.2019.02.005
Abstract PDF(1603KB) icon860 icon531
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To develop a method of determining serviceable limits of foreign object damage (FOD) in aeroengine titanium fan/compressor blades, researches of serviceable limits in typical blades were firstly conducted, then stress ratio related contour maps of FOD crack non-propagation were established based on the principle of crack growth threshold, the suitability of two crack non-propagation criteria was compared according to the TC4 titanium material fatigue durability limit strength at different stress ratios, finally, serviceable limits of tearing/crack type foreign object damages in a typical fan blade were determined by this method. The results show that, in the present maintenance books, serviceable limit requirements are different for different types of FOD and different blade regions, the main limited size of FOD serviceable limits is damage depth, the depth limitation is generally less than 1mm. The tearing/crack type FOD serviceable limits of the typical fan blade determined by the contour maps of crack non-propagation are within the range of 0.020-0.525mm, the serviceable limit distribution along the blade span can be divided into three regions: the serviceable limit in the blade root area is about 0.08mm, the serviceable limit in the blade middle area is about 0.3mm, and the serviceable limit in the blade tip area is about 0.5mm, the closer to blade root means the smaller serviceable limit.
Micro-slip properties for dry friction of blade root joints
2019, 34(2): 305-312. doi: 10.13224/j.cnki.jasp.2019.02.006
Abstract PDF(878KB) icon886 icon442
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Several contact pairs were built on the contact surface to simulate the micro-slip at the blade root joint. Control variate method was employed to gain the hysteresis loop with friction force and relative displacements in two-dimensional blade root joints contact surface under steady vibration. Analysis and assessments were carried out for parameters such as reference nodes, mesh configuration, tangential and normal loads, contact stiffness and friction coefficient, providing a new insight for investigating the micro-slip property of blade root dry friction. The results showed that when investigating the behavior of blade root joints with micro-slip model, the choices of different parameters had influence on the dry friction properties. The contact element amount affected the accuracy of the results, and the reference nodes used gave different descriptions to the hysteresis loop. Tangential load made the relative displacement in hysteresis loop different. The decrease of normal contact stiffness can increase the relative displacement and micro-slip region. The increase of tangential contact stiffness made the blade root move easier with macro-slip like rigid motion. Friction coefficient and normal pressure increased the micro-slip region, while the influence was not absolutely the same. Meanwhile, the damping effects of contact parameters were investigated by way of dissipated energy.
Modeling method of connecting bolts in centrifugal compressor containment structure
2019, 34(2): 313-320. doi: 10.13224/j.cnki.jasp.2019.02.007
Abstract PDF(1035KB) icon824 icon536
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To investigate the impact resistance of centrifugal compressor containment assembly, numerical simulation of connecting bolts in specific compressor was conducted. Four modeling methods of bolts were established, simulation results and characteristics were discussed. Verification tests on high-speed spin tester were conducted. Results indicated that the Spider multi-point coupling model, tiebreak contact algorithm, beam-shell-discrete spring model took the advantage of high computing efficiency, but made large deviation in stress, strain and impacting loads. The solid model computed slowly but could describe the interaction of the bolts and holes, showing better agreement with the test.
Numerical simulation of TC4 plates with high speed erosion of sand dust with different shapes
2019, 34(2): 321-330. doi: 10.13224/j.cnki.jasp.2019.02.008
Abstract PDF(1066KB) icon800 icon495
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The air inhalation engine containing sand dust could collide with the compressor rotor blade at a higher relative speed and produce sand dust erosion, seriously affecting the flight safety of the aircraft. The model of TC4 plate with different shapes of sand dust was established by using the smoothed particle hydrodynamics (SPH) and finite element (FE) coupling, which could better adapt to the large deformation. The typical damage forms and laws of high speed erosion of the sand dust on the surface of the TC4 plate were studied. Results showed that the smaller sand dust angle meant the deeper impact crater and the greater damage. With the sand dust hitting the plate, the depth of the pit became smaller and smaller, showing the plastic hardening process of the flat surface; under the continuous impact of the sand dust, the impact angle was affected by the sand dust, the accumulation of the damage may be flushed off the plate by sand dust and repressed back to the crater.
Investigation on flow and heat transfer characteristics of impulse squealer tip
2019, 34(2): 331-340. doi: 10.13224/j.cnki.jasp.2019.02.009
Abstract PDF(1145KB) icon806 icon446
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In order to study the aerothermal performance of impulse squealer tip, three impulse squealer and three assisted rib squealer configurations were investigated using numerical simulation method. The gap leakage flow field, tip secondary flow loss, tip total pressure loss and heat transfer coefficient were discussed in detail. The results showed that the squealer leading edge ribs suppressed the suction side branch of over tip leakage vortex, enhanced the over tip leakage flow separation in the squealer. With the same squealer depth, the relative total pressure loss of the double-ribbed squealer tips was the smallest, and the maximum decrease was up to 13% within the research range. The impulse squealer tip enhanced the leakage flow mixing in the squealer, reduced the kinetic energy of the leakage flow. With the same squealer depth, the relative total pressure loss of the impulse double-ribbed squealer tip was the smallest, and the maximum decrease was up to 18% within the research range. The impulse squealer tip reduced the leakage flow re-attachment on the cavity floor, increased the leakage flow re-attachment on the rim and rib surface of the squealer, and a high heat transfer coefficient area appeared on the rim and rib surface.
Design method of large dimension cold shield based on G-M cryocooler
2019, 34(2): 341-347. doi: 10.13224/j.cnki.jasp.2019.02.010
Abstract PDF(845KB) icon783 icon462
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The design methods of the 20K large dimension cold shield based on Gifford-Mcmahon (G-M) cryocoolers used for infrared calibration test in space environment simulation test were introduced. The cold shield with 1m×1m boundary condition, the largest dimension in China, was cooled by five G-M cryocoolers. The installation and distribution of cold shield were introduced, and the method of compensator for contraction on cooling was also described in detail. The temperature distribution and cool-down time of cold shield surface were calculated and analyzed. The design of cold shield resolved the difficulty of compensator for contraction on cooling successfully. Test results showed that the temperature on the cold shield was 15K, and the temperature uniformity was ±1K. This indicated that the actual technical performance of the cold shield met and even exceeded the design requirements.
Effects of initial temperature on the laminar combustion characteristics of CH4/RP-3 mixed fuel
2019, 34(2): 348-356. doi: 10.13224/j.cnki.jasp.2019.02.011
Abstract PDF(1036KB) icon944 icon428
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The laminar combustion characteristics of CH4/RP-3 mixed fuel were studied in a constant volume chamber at initial pressures of 0.1MPa, equivalence ratios of 0.7-1.5, methane volume fraction of 0, 0.4, 0.8 and three initial temperatures. The flame propagation photos, laminar burning velocity and Markstein length were obtained, and the effects of initial temperature on laminar burning velocity and combustion stability of CH4/RP-3 mixed fuel were analyzed. The results showed that when the flame stretch was close to 0, the nonlinear fitting method NLM2 can well predict the change of stretched flame speed with varying stretch rate, and extrapolation can obtain more accurate unstretched flame speed. The initial temperature had a great influence on the flame propagation velocity of lean mixed fuels, but little effect for chemical equivalent ratio or concentrated mixtures. The laminar burning velocities of CH4/RP-3 mixed fuel with three methane volume fractions increased with the growing initial temperature. When the initial temperature was 420K, Markstein length reduced fastest with the increase of equivalence ratio, and when the initial temperature was 480K, Markstein length reduced slowest with the increase of equivalence ratio. Under lean and stoichiometric mixture conditions, with the increase of initial temperature, Markstein length decreased and combustion stability became worse. Under rich mixture condition, Markstein length with different initial temperatures tended to the same, and the effects of initial temperature on combustion stability was small.
Atomization performance effects of aviation kerosene mixed with long straight-chain alkanes
2019, 34(2): 357-367. doi: 10.13224/j.cnki.jasp.2019.02.012
Abstract PDF(1400KB) icon704 icon454
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The intermediate products C13—C18 of algae-based aviation kerosene were blended with aviation kerosene at a ratio of 10%, and the spray atomization performance of blended fuel oil was compared. In this experiment, as the carbon number of blended linear paraffins grew, the effect of atomization on fuel spray gradually increased. Among them, the linear alkanes C18 was blended at a ratio of 10%: the maximum reduction of the atomizing cone angle was 5.07%; the average droplet speed was changed by a maximum of 17.6%; Sauters average diameter was changed by a maximum of 15%; Ohnesorge number and Weber number significant changed with increasing injection pressure, affecting the secondary breakage of droplets. In general, the addition of long linear alkanes will have a certain influence on the atomization performance of aviation kerosene.
Method to predict leakage rate of metal seal ring
2019, 34(2): 368-375. doi: 10.13224/j.cnki.jasp.2019.02.013
Abstract PDF(971KB) icon874 icon467
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Targeting the problem of estimating the leakage rate in the design of metal seal ring, a method to predict the leakage rate based on numerical calculation was proposed. This method combined the macro-structure of the sealing system and micro-surface contact deformation considerations. The overall structure of the seal was calculated firstly, and its calculated values (contact stress, contact area) were taken as the input parameters. The rough microscopic surface with the surface roughness as the evaluation index was established. Using finite element method (FEM) for contact calculation, the leak channel model was established. After the fluid properties in the leakage gap were determined, the leakage rate was calculated by computational fluid dynamics (CFD) method. Leakage rate test was performed using a sealed test bench and the calculated values were compared with the test results. The result shows that as the contact stress increases, the surface roughness decreases, and the pressure difference increases, the leakage rate of the seal system gradually decreases. With this proposed method, the aquisition of leakage rate value relies little on the test equipment, helping to predict the leakage rate of metal seal structure effectively, while playing an important role in the design and evaluation of advanced metal seal rings.
Experiment on effects of wall cooling with microchannels on performances of swirl combustor
2019, 34(2): 376-386. doi: 10.13224/j.cnki.jasp.2019.02.014
Abstract PDF(1291KB) icon820 icon469
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In order to explore the cooling application of microchannels in gas turbine lower emissions combustors, the effects of wall cooling with microchannels on the performances of swirl combustor were studied with water as the coolant. Results showed that the microchannels had significant cooling effect on the combustor walls with high temperature. When Reynolds number of coolant passing through microchannels was less than 350, the increase of Reynolds number of coolant had a significant influence on the decrease of wall temperature, but when Reynolds number was greater than 350, the decrease of wall temperature was almost negligible as the flow rate increased. At fixed values of air mass flow rate and equivalent ratio, the flame structures characterized by CH* chemiluminescence signal hardly changed as Reynolds number of coolant increased, but swirl flame contained yellow sparks or even yellow flame, leading to incomplete combustion in a relatively high Reynolds number. As Reynolds number of coolant increased, the heat transfer rate of wall was raised, which enhanced the interaction between the flame and heat transfer of microchannels during combustion and led to results such as bigger heat loss on the flame surface, more CO emission, less NOx emission and lower overall efficiency of swirl combustion.
0Numerical study on heat transfer deterioration of hydrocarbon fuel in transcritical process under influence of multiple influencing factors
2019, 34(2): 387-395. doi: 10.13224/j.cnki.jasp.2019.02.015
Abstract PDF(1039KB) icon824 icon446
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In order to deeply understand the heat transfer characteristics of supercritical hydrocarbon fuel in the process of active regeneration cooling, the heat transfer characteristics of supercritical RP-3 were numerically calculated based on the open source software OpenFOAM. The SST(shear stress transport) k-ω turbulence model was used and the physical properties of aviation kerosene alternative fuels were calculated by the generalized corresponding state law. Comparative analyses between numerical and experimental results were used to evaluate the reliability of calculation method, the average error of wall temperature was less than 3% with the heat flux ranging from 300kW/m2 to 400kW/m2. The mechanism of heat transfer deterioration was analyzed, the effects of pressure, inlet temperature and the ratio of heat flux and mass flow rate on the flow and heat transfer were discussed. It indicated that the dramatic changes of hydrocarbon fuel physical properties near the pseudo critical temperature were the main cause of heat transfer deterioration under forced convection. Improving the pressure and the ratio of heat flux and mass flow rate or decreasing the inlet temperature were effective measures to avoid the heat transfer deterioration near the pseudo critical temperature. The predictive correlation formula of heat transfer deterioration had been proposed, providing a reference for the regeneration cooling technology.
Application of unsteady preconditioning to aerodynamic interaction simulation of tiltrotor aircraft in hover
2019, 34(2): 396-409. doi: 10.13224/j.cnki.jasp.2019.02.016
Abstract PDF(2143KB) icon883 icon483
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To solve the tiltrotor aircrafts complicated flow problems of different speed scales, an unsteady pre-conditioning method and corresponding boundary conditions were developed for simultaneous solution of incompressible and compressible flows. Combined with the unstructured hybrid grid generation technique and the overlapping grid interpolation technique suitable for the complex configuration and large displacement of tiltrotor aircraft, a numerical simulation method for tiltrotor aircraft was presented. On this basis, the validity of the numerical method was verified by hovering case at first, and the principle of preconditioning parameter selection was determined. Then, the wake vortex structure evolution of the hovering configuration for the helicopter mode was investigated, and the effects of “fountain effect” and “ground effect” on the aerodynamic performance of tiltrotor were studied. The results showed that the dissipation of the wake vortex presented different scene in different azimuthal zones. And “ground effect”, coupled with “fountain effect”, suppressed the development of rotor wake. The “ground effect” affected the entire azimuthal zone instead of the zone above the wing, causing a slight increase of 5.26% in the thrust coefficient of the installed rotor relative to the isolated rotor, but the total thrust coefficient of the whole tiltrotor aircraft were only 82.46% of the isolated rotor. The conclusion shows that the preconditioning method is able to simulate the complicated flow field in the hovering configuration of the helicopter model well. Aerodynamic interaction has a significant impact on the overall aerodynamic performance of the tiltrotor aircraft.
Numerical study on source and aerodynamic characteristic of ground vortex under crosswind condition
2019, 34(2): 410-422. doi: 10.13224/j.cnki.jasp.2019.02.017
Abstract PDF(1522KB) icon879 icon469
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Numerical simulation of scaling intake duct was carried out for the purpose of exploring the source and aerodynamic characteristic of ground vortex under crosswind condition. Results showed that trailing vortex and ambient vortex were both the major contributions to the production of ground vortex under 90 degree crosswind condition. Even though there was no ambient vorticity, ground vortex could still be there under 90 degree crosswind condition as illustrated by the trailing vortex-ground vortex model. Vorticity of ground vortex increased to the maximum and then decreased with the increase of approaching flow velocity while the critical velocity ratio increased with the increase of height-to-diameter ratio. While the height-to-diameter ratio was doubled, the critical velocity ratio increased by 65% and the peak vorticity of ground vortex decreased by 30%. Total pressure loss of the intake duct increased with the decrease of approaching flow velocity ratio due to either ground vortex or flow separation.
Numerical investigation on leading-edge vortex control fornon-slender delta wing by nanosecond pulsedielectric barrier discharge actuation
2019, 34(2): 423-433. doi: 10.13224/j.cnki.jasp.2019.02.018
Abstract PDF(1463KB) icon770 icon453
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Through applying phenomenological model of nanosecond pulse dielectric barrier discharge（NS-DBD） actuation to the leading edge of delta wing, the flow control simulation was conducted over a 47° blunt-edged delta wing. The variations of lift coefficients and drag coefficients at different attack angles, as well as the evolutions of flow structure and induced vortex, were analyzed. The results show that, if ignited at the reduced frequency of F+=1.44, the actuation can obviously improve the lift coefficients before and after stall, and the drag coefficients also increased, and kept consistent with the experimental results. Chordwise vortex induced by every actuation could change the structure of the leading-edge separated shear layer and cause it to curl inwards. There were obvious negative pressure peak values on the wings upper surface for the time-averaged flow field with actuation. Also, the flow reattachment was promoted and the region of backflow was reduced under NS-DBD actuation.
A design method for propeller with arbitrary circulation distribution
2019, 34(2): 434-441. doi: 10.13224/j.cnki.jasp.2019.02.019
Abstract PDF(831KB) icon892 icon477
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A design method for high efficiency propeller with arbitrarily given circulation distribution and operating condition was presented to calculate the geometric characteristics of the propeller, including the chord length and twist angle. For comparison of the best circulation considering or disregarding the drag of the blade element, the expressions of the two best circulations were derived respectively, and the parameters influences on the best circulation distribution were analyzed. Then the propeller design method was derived inversely from the blade element momentum theory. The study on the parameter influences for efficiency shows that the ideal efficiency is closely related to dynamic pressure and disk loading. At last, several propellers were designed with different circulations and their performances were compared. The study indicates that the design method can be used to design high efficiency propeller with arbitrary circulation, at a relative error less than 7%, and the difference of design performance from the design result in the reference literature is less than 2%.
ptimization research of the exhaust height on aviation pistontwo-stroke gasoline engine
2019, 34(2): 442-450. doi: 10.13224/j.cnki.jasp.2019.02.020
Abstract PDF(1052KB) icon862 icon495
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In order to study the influence on engine performance by a variable-exhaust two-stroke engine as the unmanned aircraft power with removal of the variable exhaust system, the simulation of the cylinder's working process in the engine was established using Fire simulation software. In the model, the characteristics of the engine after removing the variable exhaust system were studied through simulation and test. The results showed that after removing the variable exhaust system under the condition of 2000r/min, 10% throttle opening and 5500r/min, 50% throttle opening, the scavenging efficiency of the engine and the output power were reduced. On this basis, using the simulation study method to optimize the exhaust outlet height parameters, the results showed that: after removing the variable system, the optimal value of the exhaust outlet height was 36.3mm, which can guarantee the common drone flight speed range. The scavenging efficiency is high under all operating conditions. The loss of engine indicator power is minimal, and the output power can satisfy the drone power demand.
Dynamic characteristics of helicopter under heavy cargo airdrop condition
2019, 34(2): 451-459. doi: 10.13224/j.cnki.jasp.2019.02.021
Abstract PDF(874KB) icon739 icon454
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In order to study the effect of cargo movement on the helicopter attitude angle during helicopter heave cargo airdrop, the helicopter CH-53D dynamic model was established. And the rationality of the helicopter dynamics model was validated by comparison of the simulation results of the model with the flight experiment data of the helicopter. Then based on the helicopter dynamic model, the dynamic model of the helicopter heavy cargo airdrop process was established by the separation method, and the trim simulation of the helicopter in these two airdrop states of hovering and forward flight was carried out. The results show that compared with the hovering airdrop, the forward flight airdrop has a better attitude maintaining ability. This is mainly reflected in the fact that the airdrop only affects the helicopters longitudinal attitude angle in the forward flight, but has a great influence on both longitudinal attitude angle and lateral attitude angles in the hovering state.
Test of nozzle side load variation during engine start up and shut down
2019, 34(2): 460-468. doi: 10.13224/j.cnki.jasp.2019.02.022
Abstract PDF(1114KB) icon796 icon455
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For the purpose of acquiring the side load of high area ratio nozzle during engine start up and shut down, the nozzle cold flow test system was established to investigate the nozzle side load variation during engine work processes, through measuring the nozzle side load using strain tube and nozzle vibration load using acceleration sensor. Test results showed that the test nozzle had three side load peaks during engine start up and shut down respectively, and the peaks corresponded to the initial normal shock transforming to steady free shock separation process, the free shock separation transforming to restricted shock separation process and the separation flow appearing “end effect” phenomenon; the occurring sequence of nozzle side load peaks during engine start up and shut down was on the contrary, and there was some hysteresis effect for the two processes; the nozzle circumferencial strain was very sensitive to the variational side load, but the nozzle axial strain was not affected by the nozzle side load at all; the variational side load was the primary factor of nozzle vibration, and the maximum acceleration peak was about 80g when the nozzle “end effect” occurred.
Transverse jet interaction characteristics on rear section of missile model
2019, 34(2): 469-478. doi: 10.13224/j.cnki.jasp.2019.02.023
Abstract PDF(1322KB) icon740 icon459
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In order to estimate the change in effectiveness of the jet in providing control forces and moments, force-testing and oil-flow tests were carried out in 2m×2m supersonic wind tunnel. The effects of a number of parameters such as the angle of attack, jet to crossflow static pressure ratio (PR) and nozzle location, were studied. Mach number ranged from 1.5 to 4.0, angle of attack from -8° to 27°, and pressure ratio from 5 to 17.6. Numerical simulation was performed and compared with tests to obtain streamlines on the surface and interaction flowfield near nozzle exit. Pitching motion effect of the missile model on jet interaction was also investigated. Result showed that the effectiveness was enhanced for the conditions considered, as the nozzles were located at the rear body; larger crossflow Mach number resulted in more drastic change with the changing angle of attack. Interaction amplification factors decreased with the increasing PR; upward jet had greater effect than downward jet. In addition, the transverse jet interaction during pitching oscillation was obviously different from the steady interaction, especially during pitching down motion and at high angle of attack. Basic aerodynamic characteristics as well as force and moment amplification factors showed hysteresis properties. Motion effect should be considered when applying the combined utilization of transverse jet and traditional fin technique.
Experiments on influence of oxygen gas intake plan on performance of Mg/CO2 engine
2019, 34(2): 479-512. doi: 10.13224/j.cnki.jasp.2019.02.024
Abstract PDF(815KB) icon689 icon422
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A type of Mg/CO2 powder rocket engine configuration and a combustion organization plan with three times intake of oxidant gas were put forward based on the research of powder rocket engines at home and broad as well as the design methods of powder burners in industry. Experimental researches on its working process were carried out. The engine combustion efficiency and chamber deposit were studied under different oxygen gas inlet plans under the oxygen to fuel ratio 4∶1, so as to provide the basis for setting the parameters of Mg/CO2 powder rocket engine multiple-start working conditions. The engine hot-experiment results showed that the flame failed to keep stable and the engine can not work normally when the oxygen to fuel ratio in combustion chamber head was too large. The highest combustion efficiency was 64.0% among all hot experiments. There were almost no deposits in combustion chamber under the oxygen gas intake plan when the amount ratio of fluidization gas, cyclone gas and lateral gas was 2∶0.5∶1.5.
Effects of modeling design on centrifugal compressor aerodynamic noise
2019, 34(2) doi: 10.13224/j.cnki.jasp.2019.02.025
Abstract PDF(1168KB) icon775 icon452
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The effects of modeling design on compressor aerodynamic noise were studied by numerical method, the calculation results of the three-dimensional flow field indicated that the modeling designed compressors and the original model satisfied the similarity criterion, and the relative error of the global performance parameters were less than 2%. The analysis of compressor flow structure further confirmed that the flow field of the modeling designed compressor was similar to that of the original model. The compressor aerodynamic noise was investigated by a hybrid computational aero-acoustic method, which combined unsteady Reynolds averaged Navier-Stokes equations and boundary element method. The results showed that the compressor aerodynamic noise was mainly composed of discrete tones and broadband noise, and the discrete tones dominated in the spectrum. The total sound pressure level of modeling designed compressor gradually reduced with the decreasing scale factor, the peaks of modeling designed compressor discrete tones were slightly lower than those of the original model, but the broadband noise was greatly enlarged. Compressor aerodynamic noise showed obvious acoustic directivity in the inlet duct nozzle, the sound pressure amplitude and directivity of the modeling designed compressor was weaker than the original model, and the trend was proportional to the scale factor.
Effect of impeller velocity coefficient on parameters ratios between pump and its reverse mode
2019, 34(2) doi: 10.13224/j.cnki.jasp.2019.02.026
Abstract PDF(797KB) icon661 icon377
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In order to study the head ratio and flow rate ratio between pump and turbine mode of pump as turbine (PAT) based on the impeller velocity coefficient, 20 single passage impellers with specific speed 23-225 were analyzed based on renormalization group (RNG) k-ε simulation by CFX. The distribution of velocity coefficient was revealed for pump mode and turbine mode, and new head ratio and flow rate ratio between pump and turbine mode based on impeller velocity coefficient were proposed. Results showed that the impeller velocity coefficient of turbine mode was higher than the pump mode. Then 6 industrial PATs were experimented in experiment rig, indicating the result by the this method had less error than the results of Stepanoff, et al. The average errors of head ratio and flow rate ratio were just 5.38% and 5.16%, respectively. The study provides a theoretical basis for the selection and performance prediction of PAT.
Adaptive robust control of electro-hydraulic position servo systemusing high speed on/off valve
2019, 34(2) doi: 10.13224/j.cnki.jasp.2019.02.027
Abstract PDF(1092KB) icon843 icon435
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A electro-hydraulic position servo system based on a high speed on/off valve (HSV) and a directional valve was designed to obtain the high-precision position control of hydraulic cylinder using HSV, in existence of large parametric uncertainties and nonlinearities. Static flow characteristic of HSV was analyzed to choose appropriate experiment frequency. Nonlinear model of hydraulic system was established with friction model and the parameters of continuous differentiable friction model were identified by particle swarm optimization (PSO) algorithm. Direct adaptive robust controller (DARC) was proposed based on nonlinear projection mapping technology and back-stepping control theory. Parametric uncertainties and nonlinearities were handled by parameter online adaptation and robust feedback in DARC. Experimental results showed that the proposed controller achieved higher control performance which was better than proportion integration differentiation (PID) controller. In tracking a sinusoidal trajectory with amplitude of 5mm, frequency of 0.4Hz, the maximum tracking error was 0.638mm, average tracking error was 0.25mm, and standard deviation of the tracking error was 0.405mm during the last cycle. This method would be of valuable guiding significance to the development of digital servo control system.

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