2018 Vol. 33, No. 3

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Time-related steady heat transfer experiments in rotating disk cavity
2018, 33(3): 513-520. doi: 10.13224/j.cnki.jasp.2018.03.001
Abstract PDF(2333KB) icon1199 icon834
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Errors in steady heat transfer experiments increase if it is measured before steady state, and the half-life period of errors of average Nusselt number is about 2500~2700s in general conditions. In order to modify the state of heat transfer experiments, rotating disk cavity heat transfer experiments were performed by transient numerical simulation. Results presented showed that it was a long time before steady state in heat transfer experiment of cavity. An approach of predicting steady time and allowable measurement time was developed by permissive errors of experiments, and allowable measurement time can be pre-calculated before experiments by Fourier number. Its also suggested that the sensors be observed per minutes by regularity of logarithm until the numbers of sensors are constant, then the experiment is in steady state.
Effects of blowing ratio on turbine vane suction side film cooling under different turbulence intensity conditions
2018, 33(3): 521-529. doi: 10.13224/j.cnki.jasp.2018.03.002
Abstract PDF(4066KB) icon1266 icon830
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The effects of blowing ratio on turbine vane film cooling under different mainstream turbulence intensity conditions were studied using the transient heat transfer measurement technique with narrow-band thermochromic liquid crystal in the whole region. The spatial distributions of film cooling effectiveness of cylindrical holes on the suction side of a turbine vane and surface heat transfer coefficient ratio in whole region were obtained. The results showed that the mixing effect and interaction intensity of film jets and mainstream changed with the mainstream turbulence intensity, so the effects of blowing ratio on the film cooling effectiveness and surface heat transfer coefficient ratio were different under different mainstream turbulence intensities. In experimental conditions, when the mainstream turbulence intensity was small, the film coverage and cooling effectiveness rapidly deteriorated with the increase of blowing ratio. However, the change of blowing ratio had relatively weaker effect under large mainstream turbulence intensity, especially in the far downstream region. Under the same mainstream turbulence intensity conditions, the increase of blowing ratio can enhance the surface heat transfer coefficient. However, the enhancement effect was relatively small under large mainstream turbulence intensity. Under the same blowing ratio, the surface heat transfer coefficient was relatively small when the turbulence intensity was high.
Heating characteristics of aero-engine nose cone with film-heating anti-icing systemA
2018, 33(3): 530-539. doi: 10.13224/j.cnki.jasp.2018.03.003
Abstract PDF(4515KB) icon1184 icon890
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For the film heating anti-icing system used in composite aero-engine nose cone, a computational fluid dynamics method was adopted to study the internal jet impingement heat transfer and external film heating efficiency. Two-dimensional axisymmetric algorithm was developed and compared with the results calculated by three-dimensional algorithm. A hot-air blowing experimental apparatus was built up and the infrared thermometer and thermocouple were used to verify the numerical simulation method. The effects of Reynolds number, relative impingement distance and structure parameters of film slot on heat transfer characteristics were comprehensively investigated. Results show that increasing Reynolds number is conducive to improving the internal jet impingement heat transfer and external film heating efficiency. The optimal value of relative impingement distance increases with the increasing Reynolds number, and the optimal value is between 5 and 8 when Reynolds number is between 10000 and 40000. Opening film slot can significantly increase the temperature of exterior surface, and heating efficiency is related to the width and location of film slot. Opening film slot at leading edge can also enhance jet impingement heat transfer.
Icing wind tunnel test evaluation on anti-icing effects of hydrophobic coating on two parallelized square cylinders
2018, 33(3): 540-548. doi: 10.13224/j.cnki.jasp.2018.03.004
Abstract PDF(2636KB) icon1090 icon721
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Anti-icing effects of different nano hydrophobic coatings on two parallelized square cylinders test model were studied using icing experimental method in the main test section of 0.3m×0.2m icing wind tunnel under different icing weather conditions.The ice shapes on left and right parallelized square cylinders test model were measured and compared respectively.The quantitative method of evaluating anti-icing effect was established on the basis of nine geometric characteristics parameters of ice profile.The nondimensional deviation of ice profile geometric characteristics parameters were calculated and analyzed between the coated model and the clean model.The study shows that the quantitative test evaluation method based on ice profile geometric characteristics parameters can evaluate the anti-icing effect of nano hydrophobic coating.The silicone rubber coating and other coatings added in different nano particles have some anti-icing capability.The silicone rubber coating added in different proportion of nano particles show comparative anti-icing capability compared with the silicone rubber coating in the present study.Adding small amount of nano hydrophobic particles in the silicone rubber coating can construct some micro-nano structures, which can enhance the hydrophobic and anti-icing effects.Therefore, it is a valuable way to fabricate anti-icing coating by adding different nano hydrophobic particles into the silicone rubber coating.But it is not easy for the nano hydrophobic particles to form a stable micro-nano structures with hydrophobic and anti-icing performance on the silicone rubber coating just by physical mixing and stirring methods.The nano hydrophobic coating can reduce the icing velocity, but cant stop icing phenomena completely.
Visualization on spray distribution of close-coupled fuel injector and strut with cavity flameholder system
2018, 33(3): 549-556. doi: 10.13224/j.cnki.jasp.2018.03.005
Abstract PDF(2938KB) icon1300 icon791
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Spray distribution is closely related to the fuel supply methods, fuel-air distribution ratio, flame stability and flame propagation properties of flameholders. Taking RP-3 as atomization medium, the spray distribution characteristics of close-coupled fuel injector and strut with cavity flameholder system were visualized by high-speed photography and laser sheet/photography, under the condition of incoming flow Mach number 0.2, incoming flow temperature varying from 10℃ to 400℃, the distance of fuel injector and stabilizer kept as 31.5mm and the downstream injection direction. Meanwhile, the effects of incoming flow temperature and fuel-to-air momentum flux ratio on spray distribution trajectory were studied as well. The result showed that, downstream injection close-coupled fuel injector and strut with cavity folder system was benificial to the fuel atomization by splashing fuel jet at the leading edge of strut. After the splashing, a part of fuel was distributed on the surface of strut as fuel film and atomized further at the leading edge and trailing edge of cavity, during which higher incoming flow temperature led to faster evaporation. And another part of fuel spray was atomized as cross-flow. Under the same incoming flow temperature, the axial-direction distribution distance and cross-direction penetration depth of spray increased with the fuel-to-air momentum flux ratio. With the increase of air incoming flow temperature, penetration depth increased and fuel-to-air momentum flux ratios effect to spray distribution became more obvious.
Influence of air-fuel ratio on accuracy of combustion efficiency and exhaust emission under gas analysis method
2018, 33(3): 557-564. doi: 10.13224/j.cnki.jasp.2018.03.006
Abstract PDF(1339KB) icon1431 icon744
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Based on the gas analysis error of a single position, the influence law of the fuel-air ratio error between gas analysis and flow measurement on the testing precision of combustion efficiency and exhaust emission was founded for the current sampling mode of primary combustor, afterburner and gas turbine engine. The data were valid for primary combustor test by swing mode when fuel-air ratio error was less than 5.1% between flow measurement and gas analysis; meanwhile, the error of combustion efficiency was less than 0.5% and sampling density was considered enough. The error of fuel-air ratio of flow measurement to gas analysis was large due to less sampling density in afterburner and gas turbine engine, the precision of combustion efficiency was also affected by fuel-air ratio and the volume fraction of CO. It indicates that enough sampling density for gas analysis is necessary for high test precision.
Effect of structure on heat transfer performance in double-layered microchannel heat sinks
2018, 33(3): 565-572. doi: 10.13224/j.cnki.jasp.2018.03.007
Abstract PDF(2442KB) icon1662 icon806
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A double-layered microchannel heat sink with difference structure in each layer (B) was designed, and compared with structure A (the same complex structure in each layer) to reduce pressure drop and main good heat transfer performance. The effects of parallel flow, counter flow and different structures (PA,PB,CA,CB) on heat transfer performance were studied numerically. Moreover, the effect of synergy relationship between flow field and temperature field on heat transfer was analyzed by field synergy principle. The results showed that the average bottom temperature of parallel flow PA and PB was lower than that of counter flow CA and CB when Reynolds number ranged from 0 to 140. However, the average bottom temperature from low to high followed by PB, CB, PA and CA(when Reynolds number ranged from 140 to 250). From it, structure PB was adopted if there were high requirements for bottom temperature of microelectronics chips.From the view point of comprehensive heat transfer performance, the heat transfer performance and synergy angle of PB was better and smaller than others, indicating that it could improve the synergy relationship between flow field and temperature field obviously.
Plasma assisted methane ignition based on shock tube
2018, 33(3): 572-580. doi: 10.13224/j.cnki.jasp.2018.03.008
Abstract PDF(2434KB) icon1063 icon708
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The plasma discharge unit was designed based on the shock tube experiment system, and the plasma discharge VA characteristic curve was measured. The auto ignition delay, ignition delay with continuous discharge and ignition delay after the discharge shut down were measured. The chemical reaction path in the methane ignition process was analyzed. The results showed that the plasma discharge voltage and current did not present the same change trend. The gas resistance changed continuously in the discharge process. Little discharge energy (less than 4J) can effectively reduce the methane ignition delay. The particles produced during the discharge could reduce the methane ignition delay in a certain degree after the power was shut down. The influence mechanism of plasma assisted methane ignition under the low or high ignition temperature condition was basically the same. The effects of continuous discharge were more apparent to reduce the methane ignition delay time when the ignition temperature was relatively low (less than 1000K) or high (greater than 1600K). The methane ignition delay could be shortened in an order of magnitude or more than one order of magnitude. It was a result of coupling effect of ignition temperature and plasma concentration act to the methane ignition delay.
Effect of dynamic behaviour on its impingement characteristics for droplets
2018, 33(3): 581-589. doi: 10.13224/j.cnki.jasp.2018.03.009
Abstract PDF(2489KB) icon1126 icon844
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A piezoelectric mono-dispersed droplet generator was designed to study the deformation of droplets under the aerodynamic force by the high speed imaging system. The non-spherical drag model was established for the deformed water droplets. The process of water droplets impinging on the NACA23012 airfoil was simulated while the breakup model and splash model were introduced into Eulerian model. The simulated results were compared with the results from traditional model. It was found that the drag coefficient of water droplets increased because of the deformation. When the Reynolds number was larger than 500, water drag coefficient curve broke away with the spherical drag curve gradually and grew close to the disc drag coefficient curve. The droplet trajectory was affected because of the change of the drops drag properties, making the droplet follow with the air. The mass loss from splashing decreased the local collection coefficient on the airfoil, which was in good agreement with the experiment data.
Effects of structural parameters of effusion holes on adiabatic film cooling effectiveness over transverse corrugated surface
2018, 33(3): 590-596. doi: 10.13224/j.cnki.jasp.2018.03.010
Abstract PDF(4152KB) icon1299 icon756
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Numerical simulation was carried out to study the effusion cooling on a specific transverse corrugated heat-shield used in aero-engine afterburner. Three main geometric parameters, including spanwise-to-streamwise pitch ratio, hole diameter and perforated percentage, were taken into consideration. Result showed that, in the wavy valley of transverse corrugated surface, the coolant jets ejected from adjacent holes were prone to interact each other, thus forming more coolant accumulation. Due to this feature, the adiabatic wall temperature on the wavy valley of transverse corrugated surface was relatively lower than that on the wavy peak. In general, reducing the hole diameter and enlarging the perforated percentage were illustrated to be significantly helpful to enhance the film cooling effectiveness under the same coolant usage for a given protected area, especially in the front developing zone of an effusion cooling scheme. Besides, the effusion holes arranged in a super-long-diamond mode where the streamwise hole-to-hole pitch was bigger than spanwise hole-to-hole pitch showed more favorable. However, the effect of spanwise-to-streamwise pitch ratio on the laterally-averaged adiabatic film cooling effectiveness was very weak at low blowing ratio.
Model of critical heat flux for spray cooling under vibration environment
2018, 33(3): 597-603. doi: 10.13224/j.cnki.jasp.2018.03.011
Abstract PDF(2097KB) icon864 icon740
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The effect of vibration environment on critical heat flux (CHF) of spray cooling was studied. The point-based CHF model under vibration environment was built by defining factor which represented the degree of deviating from the inscription state, based on the CHF model in normal environment. Three operation modes were compared, and the operation mode one had 0.98% and 1.17% increase in the period-average CHF compared with the others. In the operation mode one, the curve of CHF showed a bimodal structure, and the minimum CHF of the second half of period was larger than that of the first half of period. The minimum CHF was 3.02% lower than the maximum CHF. The larger vibration amplitude led to the greater decrease of the CHF. The average CHF with 1.0mm amplitude was 1.74% lower than that with 0.2mm amplitude. The influence of spray angle was discussed. The average CHF showed 4.83% and 16.21% drop in 55.8° and 90° cases respectively, compared with 30° spray angle case. The difference between the minimum CHF of the second half of period and maximum CHF was smaller in larger spray angle case. Using nozzle with small spray angle could reduce the negative effect of vibration.
Segmentation algorithm for temperature indicating paint image based on FCM clustering
2018, 33(3): 604-610. doi: 10.13224/j.cnki.jasp.2018.03.012
Abstract PDF(2108KB) icon895 icon776
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According to the image features and the related experimental results, a temperature indicating paint(TIP) image segmentation algorithm based on fuzzy C-means (FCM) clustering was proposed. Taking the FCM clustering algorithm as the core, the algorithm employed the bilateral filter to smooth the image to improve the segmentation quality. The color space conversion was used to improve the iterative efficiency of the image clustering. Experiments showed that the algorithm can enhance the feature information needed in the process of the interpretation of the TIP. The algorithm can extract isotherms that cant be recognized by naked eye and the temperature measurement error was ±10℃. The algorithm has good application effect and meets the engineering requirements, so it has been applied to the development of automatic interpretation software for TIP.
Measures to improve anti-knock quality for four-stroke ignited kerosene aviation engine
2018, 33(3): 611-619. doi: 10.13224/j.cnki.jasp.2018.03.013
Abstract PDF(4353KB) icon1044 icon651
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A one-dimensional performance simulation for a four-stroke ignited turbocharging aviation engine with different fuels was made by an engine performance simulation software GT-Power to optimize the anti-knock quality. Through the reasonable adjustment of the compression ratio, boost pressure, air-fuel ratio, cylinder diameter, ignition timing, knock tendency of the engine using the new fuel was optimized, and engines main output parameters were roughly maintained. When replacing the No.93 gasoline fuel with a new type fuel of 61 octane number, the power can reach 89% of the original power output after using the method without expanding the diameter of the cylinder and 95% after using the method of expanding the diameter of the cylinder; the specific fuel consumption increased about 5.4% and 6.1%, respectively; and the exhaust temperature increased about 11.4% and 13.4%, respectively.
Experiment on convective heat transfer of aviation keroseneRP-3 in vertical micro-tube at supercritical pressure
2018, 33(3): 620-657. doi: 10.13224/j.cnki.jasp.2018.03.014
Abstract PDF(2631KB) icon858 icon570
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Convective heat transfer of supercritical China aviation fuel RP-3 in vertical micro-tube (inner diameter of 1.09mm) was experimentally investigated. Influences of system pressure, heat flux, flow direction and buoyancy on heat transfer were analyzed. Wall heat fluxes (180-460kW/m2), system import pressure (3-5MPa) and inlet Reynolds number (3200-10200) were maintained in experiments. The result showed that the buoyancy force deteriorated the heat transfer of downward flow in the entrance of test section; system pressure affected the convective heat transfer mainly by the impact of fluid thermal properties; effects of different flow directions on convection heat transfer were very significant. Overall heat transfer was strengthened for downward flow and decreased for upward flow.
Experiment on flow resistance of n-decane invertical tube at supercritical pressure
2018, 33(3): 628-634. doi: 10.13224/j.cnki.jasp.2018.03.015
Abstract PDF(1771KB) icon902 icon588
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The flow resistance characteristics under heating condition of n-decane in the vertical miniature tube at supercritical pressure were investigated. The influence of heat flux, system pressure and inlet temperature was mainly studied. The result indicated that, the pressure drop due to frictional resistance in tube decreased with the rise of heat flux when fluid temperature was not very high. When temperature rose to the pseudocritical point, due to the effect of thermal physical properties, the pressure drop increased. And the lower system pressure led to more violent pressure drop changes. While the temperature of fluid was higher than the pseudo-critical temperature, pressure drop went up with increases of heat flux because of steady thermal physical properties. As a result, an empirical correlation of frictional resistance was derived for different temperatures and ratios of heat flux to mass velocity.
Knocking control of direct injection piston-type aviation kerosene engine
2018, 33(3): 635-641. doi: 10.13224/j.cnki.jasp.2018.03.016
Abstract PDF(1911KB) icon1052 icon559
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Focusing on knocking-influenced factors including excess air coefficient, spark advance angle and compression ratio, investigations on methods to suppress the knocking of piston-type aviation kerosene engine and sensitivity analysis of relevant factors were conducted on a self-developed engine. The results showed that the decrease of excess air coefficient cannot suppress the knocking of aviation kerosene effectively; retarding ignition timing can reduce knocking intensity, but if the spark advance angle was delayed till the knocking was eliminated, the combustion thermal efficiency and output power lost 10%-15%; reducing compression ratio turned out to be effective to restrain the knocking of aviation kerosene, but when compression ratio was reduced from 9 to 7, the output power had an approximate 30% loss. Sensitivity analysis shows that knocking intensity of aviation kerosene is most sensitive to the change of compression ratio, and the change of the excess air coefficient of mixture slightly influences the knocking intensity.
Effect of inlet distortion on performance of combustion chamber
2018, 33(3): 642-648. doi: 10.13224/j.cnki.jasp.2018.03.017
Abstract PDF(2820KB) icon1106 icon568
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Under the non-design condition, there is obvious flow distortion in the compressor flow. The obvious non-uniform air field from the outlet of the compressor has an important influence on the performance of the combustion chamber. The differences of combustor performance under the uniform and non-uniform inlet flow conditions with a detailed chemical reaction kinetics and a diffusion flamelet model were studied. Calculated results were in good agreement with the experimental data. Results showed that the non-uniform inlet flow destroyed the symmetry of the flow field and resulted in an obvious reduction in combustion efficiency. The combustion efficiency was improved by increasing the area of primary combustion holes.
Interface failure analysis and robust design method in rotor structural system
2018, 33(3): 649-656. doi: 10.13224/j.cnki.jasp.2018.03.018
Abstract PDF(2142KB) icon1029 icon579
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For the contact status variation of mechanical interface making mechanical properties vary in rotors with non-straight structures, the non-robust problem of rotor systems dynamics characteristic was analyzed, and a novel robust design method of contact status was presented. Result showed that this method analyzed the damage and failure process of mechanical interface in non-straight structural rotor system structural properties optimal design, and established an optimal design for structural properties. This method decreased the sensitivity of mechanical properties under loads and environment. An optimal design of the spline coupling structure in turbine rotor was implemented. The results indicated that the contact stress of optimal solution kept far from stress-constrained boundary under the condition of manufacturing errors. The mechanical properties of non-straight structural rotor system with mechanical interface were more robust than before. The robust design method of mechanical interface shows preferable engineering value.
Creep constitutive model of Ni3Al-based single crystal superalloy
2018, 33(3): 657-662. doi: 10.13224/j.cnki.jasp.2018.03.019
Abstract PDF(1577KB) icon854 icon551
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Combined with the microscopic mechanism of the creep behavior of Ni3Al-based single crystal superalloy, the creep constitutive model based on the crystal slip theory was established to describe the creep behavior of Ni3Al-based single crystal superalloy. And the finite element implementation of the constitutive model established was conducted through the UPFs redevelopment platform provided by ANSYS. Using the creep test data, the model parameters of two kinds of Ni3Al-based materials were obtained based on genetic algorithm. Using the creep constitutive model established, the finite element simulation of high temperature tensile specimens of two kinds of Ni3Al-based materials was carried out, and the results had a good agreement with the test results. It shows that the creep constitutive model based on the crystal slip theory is reasonable and it can simulate three stages of creep behavior of Ni3Al-based single crystal superalloy well. Therefore, it has a definite application value.
Local and global stability of pneumatic valveschatter
2018, 33(3): 663-670. doi: 10.13224/j.cnki.jasp.2018.03.020
Abstract PDF(2653KB) icon960 icon541
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Based on a modified Coulomb friction force model, the nonlinear stability characteristics of pneumatic valves' chatter were theoretically analyzed, and the regions of instability, local and global stability were developed, which interpreted the inevitability and occasionality of valve chatter at the local stable region. Taking a safety valve as the research object, the AMESim model of the safety valve system was constructed, the local and global stability regions, and the effect of Coulomb friction were obtained. Moreover, validation of the stability analysis was performed by the pneumatic experiment of the safety valve under various friction forces and various disturbance conditions. Results indicated there was a local stability region of small disturbance stability and large disturbance instability, showing that the safety valve was stable at exhaust experiment and unstable at exhaust and vibration experiment from the view of simulation. Moreover, with the increase of the Coulomb friction force, the stability and anti-disturbance ability of the safety valve system were enhanced, and the validation of nonlinear stability analysis was improved by the exhaust and vibration experiment of the safety valve.
Impact resistance performances of resin matrix composite single lap joints reinforced by Z-pin
2018, 33(3): 671-682. doi: 10.13224/j.cnki.jasp.2018.03.021
Abstract PDF(5897KB) icon949 icon606
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To study the impact resistance performances of resin matrix composite joints reinforced by Z-pin, single lap joint specimens reinforced by Z-pin were prepared. The crack propagation along Z-pin/laminates interface was compared with different resins matrix of Z-pin. Z-pin pullout and lap shear tests were carried out to study the after-impact pullout strength of Z-pin and after-impact shear strength of single lap joint, respectively. The ultrasonic C-scan method combined with finite element simulation was utilized to explore the delamination damage area of joint interface. The results showed that compared with the BMI resin matrix Z-pin, the resistance performance between epoxy Z-pin/epoxy laminates was stronger at the same impact energy. With the increase of impact energy, the crack propagation was more significant. Z-pin reinforced resin matrix composites remarkably reduced delamination damage area and improved the after-inpact shear strength. The delamination damage area of joint reinforced by Z-pin was 40%, and its reduction of after-impact shear strength was 24.89% when Z-pins volume fraction was 1.5% and diameter was 0.5mm.With the increase of Z-pin volume fraction, the delamination damage area decreased gradually, while the after-impact shear strength increased firstly and then decreased. The damage area of lap surface increased as the increment of Z-pin diameter while the after-impact shear strength decreased. The results of finite element modeling were consistent with the test results.
Research progress on flight tests of HIFiRE project based on scramjet
2018, 33(3): 683-695. doi: 10.13224/j.cnki.jasp.2018.03.022
Abstract PDF(4615KB) icon1323 icon730
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The aerodynamic characteristics and engine performance of the vehicle in the nearspace have been the focus of the research on the hypersonic projects in various countries. To explore the boundary layer transition, the shock boundary layer interaction and the aerodynamic heating effect, America and Australia led a project called HIFiRE in 2006 and investigated a series of innovation for this kind of vehicles by using sounding rocket to verify key techniques. Height range 20-38km and speed range flight Mach number 4-8 were the major concerns. Flight test scheme was arranged with the method of single technology verification and system integration. With the combination of propulsion system, the gliding waverider carried out cruise flight, at last, overall performance of high lift-to-drag ratio vehicle with scramjet was tested at hypersonic speed. The results showed that: (1) the boundary layer transition height of the test vehicle was in the range of 35~25km; (2) the maximum lift-to-drag ratio of waverider-body vehicle at flight Mach number 7 was 5.6; (3) during the flight test of scramjet, the speed of the vehicle was accelerated from flight Mach number 5.5 to flight Mach number 8.5 at a constant dynamic pressure of 86.2kPa, and the engine realized mode transition from sub combustion to super combustion.
Flow control of hypersonic reentry vehicle based on multi-jets interaction
2018, 33(3): 696-702. doi: 10.13224/j.cnki.jasp.2018.03.023
Abstract PDF(4526KB) icon1128 icon592
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A concept of multi-jets flow control was proposed for a hypersonic reentry vehicle. The high pressure air behind the bow shock flowed into the tunnel through the multihole head, and then sprayed out through the downstream multi-jets arrays. The 3-D Reynold-averaged Navier-Stokes (RANS) simulations based on Fluent software were conducted to study the effect of multi-jets configuration at Mach number of 6,height of 25km. The results showed that the multi-jets flow induced a drag coefficient increment for both the side-hole down-bottom (SH-DB) case and the side-hole upper-bottom (SH-UB) case. The increment of lift coefficient and head-down moment was observed for the SH-DB case, and the decrement of lift coefficient and head-up moment was observed for the SH-UB case. This study provides a method of using non-movement aerodynamic control surface to produce control moment, and also a reference for combination control of hypersonic reentry vehicle.
Design and dynamic analysis of a flapping wing air vehicle
2018, 33(3): 703-710. doi: 10.13224/j.cnki.jasp.2018.03.024
Abstract PDF(3010KB) icon1461 icon745
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To improve the design of flapping-wing air vehicles and have a better understanding of their dynamics, a prototype of a bird-like air vehicle with foldable flapping wings was designed, and the dynamics of the prototype was carefully analyzed. First, the flapping mechanism based on crank link was designed, meanwhile the kinematic model of the mechanism was established, and the kinetic equations of the mechanism were deduced via Lagrangian method. Then the estimation model of the aerodynamic forces on the flapping wings was set up using strip theory, and the aerodynamic parameters of both the straight and the foldable flapping wings, under the time symmetric and time asymmetric flapping patterns, were calculated. The results showed that higher lift forces could be obtained when the foldable wings underwent asymmetrical flapping, which was attributed to lower resisted forces during the up-stroke periods of the foldable wings. Finally, with the commercial software package ADAMS, the dynamics forces at the critical linkage positions of the flapping mechanism were simulated, and the results provided a suggestion on strengthening the flapping mechanism.
Experiment on characteristics of plasma synthetic jet actuator with multiple slots under low pressure condition
2018, 33(3): 711-716. doi: 10.13224/j.cnki.jasp.2018.03.025
Abstract PDF(1646KB) icon724 icon525
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A large interval plasma synthetic jet actuator (PSJA) with multiple slots under low pressure condition was designed to control the flow-field for high-altitude vehicle.Since the breakdown voltage decreased rapidly under low pressure condition, the distance of cathode and anode can be extended to 26mm, much larger than that of traditional PSJA. This optimization also could make the cavity and output of actuator extend remarkably. The discharge characteristics and flow-field were researched by electric parameter measurement system and high-speed schlieren technology, respectively.The results showed that the initial jet velocity of the actuator reached 761m/s, indicating the actuator had excellent application prospect in high speed flow control.In addition, comparing with the normal perforated jet generated by the actuator, the compression wave and plasma jet appeared in an ellipse shape with a large flat portion, contributing to enhance the perturbation and momentum exchange capability.
Aerodynamic optimization design of core driven fan stage on balance of two modes
2018, 33(3): 717-728. doi: 10.13224/j.cnki.jasp.2018.03.026
Abstract PDF(7348KB) icon900 icon533
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An aerodynamic design method was proposed for core driven fan stages on balances of the single and double bypass modes. Combining the S2 stream surface through-flow calculation with a genetic algorithm, the optimal inlet guide vane (IGV) outlet angle, closed angle and pressure ratio distributions in the two modes along the blade spans were found, achieving the balance on the rotor aerodynamic design. The key geometric parameters of the variable IGV were determined according to the study on the influences of the IGV profile camber and installation angle on flow losses in the two modes, achieving the balance on the IGV design. The stator blade design was conducted by using multi-point optimization method, achieving the balance on the stator aerodynamic design. Three-dimensional flow fields of a designed core driven fan stage were numerically simulated, and the results showed that the isentropy efficiency at the design point reached 88.05% and 87.17% in single and double bypass mode, respectively under the premise of satisfying the total pressure ratio and mass flow rate in two modes, and the stability margins in the two modes reached 15.65% and 16.28%, respectively.
Effect of passive jet vortex on high-speed compressor cascade under different angles of attack
2018, 33(3): 729-740. doi: 10.13224/j.cnki.jasp.2018.03.027
Abstract PDF(6984KB) icon1117 icon573
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The application of passive jet vortex (PJV) on a high-speed compressor cascade for flow separation control was studied numerically. The effectiveness of the technique at off-design conditions was investigated. Results indicated that the PJV could reduce the total pressure loss coefficient by 5.2% at the designed angle of attack, and by 7.8% under different angles of attack, validating its high control efficiency and good adaptability. With the increase of the angle of attack, the flow separation on the blade suction surface would take place earlier and the distance between the jet exit and the separation region would decrease, which could strengthen the effect of PJV in enhancing momentum exchange and reorganizing the vortex structures like the passage vortex and the concentrated shed vortex within the passage, thus delaying the flow separation and reducing flow losses. Taking different angles of attack into consideration, it is suggested that the PJV be located near the upstream separation region. The optimum location of the jet is at 40% axial chord length from the blade leading edge.
Research and simulation of hypersonic aircraft thermal management system and its control model
2018, 33(3): 741-751. doi: 10.13224/j.cnki.jasp.2018.03.028
Abstract PDF(3492KB) icon1312 icon707
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A model of thermal management system (TMS) for hypersonic aircraft was designed based on single phase fluid circuit. Corresponding thermal control strategy and heat sink allocation model were presented for improving the cooling ability of heat sinks and solving the problem of lacking cold source. The thermal control strategy was implemented based on the algorithms of system identification and heat load forecast, and the thermal control model which aimed for overcoming the control delay caused by thermal inertia was optimized by adding an energy balance model and thermal feedback. Moreover, the heat sink allocation model based on heat sink cooling capacity evaluation and heat load matching was designed for higher usage of cooling source. Furthermore, MATLAB/Simulink was employed for testing TMS model and control strategy. Simulation work shows that: TMS model can meet the cooling requirement of hypersonic aircraft; current control model of smaller overshoot and higher decay rate is better than thermal feedback control model; the heat sink allocation model can obviously save cooling source in whole fly profile, further utilize various heat sinks more sufficient.
Analysis on oil film characteristics of turbocharger bearing based ontwo-phase flow
2018, 33(3): 752-762. doi: 10.13224/j.cnki.jasp.2018.03.029
Abstract PDF(5492KB) icon786 icon470
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The static characteristics of inner oil film of turbocharger semi-floating ring bearing were calculated by CFD method. For the inner oil film with axial through grooves, the distribution of oil film pressure and air-phase volume fraction were predicted considering the influence of two-phase flow cavitation and non-Newton fluid. The change rules of oil film bearing capacity and friction power losses with the journal speeds, eccentricity ratio, oil temperature and pressure were also evaluated respectively. The results showed that the uppermost impact factors to friction power losses were oil temperature and journal speed, while the rare relationship with the position of through axial grooves and the cavitation at the negative pressure zone was also found. The oil film bearing capacity can be improved by increasing the eccentricity ratio and oil pressure, or cooling the oil temperature. However, the law of variation with speed up was not consistent. Simultaneously, it was beneficial for alleviating air-phase volume fraction to reduce the eccentricity ratio and oil temperature, or raise the oil pressure.
Analysis of co-work for air turbo rocket
2018, 33(3): 763-768. doi: 10.13224/j.cnki.jasp.2018.03.030
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Abstract:
Based on the principle of air turbo rocket, the condition, equation and line of co-work and its influence factors were presented. According to the co-working equation, the influence law of area of the throat for nozzle and total temperature of gas at the inlet of turbine on the co-working line was given. The result showed that the mass flow rate of air for the engine increased and the pressure ratio of compressor decreased as the numerical value of area of the throat for nozzle or total temperature of gas at the inlet of turbine increased on the same rotational velocity line, which made the co-working line move toward lower right direction. The influence law of area of the throat for nozzle and total temperature of gas at the inlet of turbine on the co-working line was similar, but the influence effect of area of the throat for nozzle was more obvious.

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