2013 Vol. 28, No. 12

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Parameters matching of ultralight electric aircraft propulsion system
KANG Gui-wen, HU Yu, LI Ya-dong, JIANG Wen-hui
2013, 28(12): 2641-2647.
Abstract PDF(1044KB) icon2036 icon1228
Abstract:
Combined with a certain ultralight electric aircraft's design parameters, the layout of aircraft electric propulsion system, the principles and steps of the parameter matching of electric propulsion system were presented. The methods of parameter matching and performance verification of electric propulsion system were put forward. The feasibility of the system was verified from the mass of propulsion system, dynamics and economics. The maximum level flight speed of the reference aircraft is 175.5km/h, greater than the maximum level flight speed of 170km/h, which is design requirement, in compliance with the requirement of dynamic performance. The operation cost of electric propulsion system is RMB 6.8 yuan/h that is close to the 1/8 of the operation cost of piston engine with similar power. Compared with three electric aircrafts, the reference aircraft's power to mass ratio is still high up to 0.0842kW/kg, which is acceptable.
Unsteady numerical simulation of the viscous flow fields of the propeller
ZHANG Liu, LIU Li-tao, ZHANG Rong-ping, HUANG ZHi-yuan
2013, 28(12): 2648-2654.
Abstract PDF(1357KB) icon1846 icon1147
Abstract:
The viscous flow fields of a propeller with six blades have been numerically simulated with unsteady N-S equations based on structured sliding grids of multiple blocks. The rotational subzone containing the propeller and the stationary subzone was constructed separately based on MFR(multiple frames of reference),proving this is an effective approach to resolve the problems involving relative rotation of the propeller. The data of the calculation and the experiment agreed very well and proved that the method had good accuracy to simulate the fluids of a propeller. Then the complicated flow fields behind the propeller with advanced ratio of 0.90 and 0.75 were analyzed, and the static and dynamic features of the propeller trailing vortex the same as the phenomenon in the test were achieved: two opposite layers were incorporated into the propeller trailing vortex. The rules influenced by the propeller on the axial velocity were obtained: the increase of the income flow velocity in the area of 45% and 70% of the radius of the blade after the propeller is larger than the area of 90% of the radius; with the decrease of the advance ratio, the axial velocity still increases, and the area of the 90% of the radius almost keep unchanged.
Calculation of free-wake of forward flying rotor in ground effect
XIN Ji, LI Pan, CHEN Ren-liang
2013, 28(12): 2655-2662.
Abstract PDF(1429KB) icon1701 icon1115
Abstract:
A free-wake based model was developed to predict the flow field and performance of a forward flying rotor in ground effect.In order to expand the application range of the model,the ground was modeled using surface panel method to simulate the influence of ground upon the flow field.For further improving the prediction convergence and accuracy,modification measures such as rectifying the wake vortices below the ground plane proportionally and distributing the ground panels circularly were incorporated into the model.The prediction results show that as the advance ratio increases,the flow regime below the rotor changes from recirculation to ground vortex mode.When rotor gets into the recirculation regime at extremely low advance ratio,the downwash velocity across rotor leading edge is very large.Which leads to an unexpected phenomenon that the rotor thrust decreases and the required rotor power almost keeps constant while the advance ratio increases.The predicted characteristic values of rotor aerodynamics at different advance ratios were then compared with experimental results and conformed well,proving the accuracy of the newly founded model.
Numerical simulation of ice accretions on aircraft wing
LI Xin, BAI Jun-qiang, WANG Kun
2013, 28(12): 2663-2670.
Abstract PDF(1421KB) icon1781 icon1006
Abstract:
Ice accretions on three-element airfoils and MS-317 swept wing were predicted by using CFD method. Based on Eulerian two phase flow theory, the governing equations for air and droplets were solved by using partition algorithm to obtain the water collection efficiency. The amount of ice accreted was calculated by solving the 3-D ice accretions model, and the predicted ice shape was compared with those of experimental and ice accretions software LEWICE3D results. The results show that the precision of the approach and algorithm is good. Although there are some discrepancies between the predicted ice shape and experimental ice shape, the error is less than 13.1% in terms of the maximum thickness, and the predicted ice shape is basically the same with the experiment data in terms of type and volume.
RCS characteristic of S-shaped nozzle with different outlet shapes
LI Yue-feng, YANG Qing-zhen, LI Xiang, HUAN Xia
2013, 28(12): 2671-2677.
Abstract PDF(1243KB) icon1857 icon1045
Abstract:
Based on the expressions of the super-elliptic method, the center-line and proportion variation patterns, three types of S-shaped nozzle with different outlet shape were designed. A program was developed to combine the equivalent edge currents(EEC) method and iterative physical optic (IPO) method. The EEC method was applied to calculate the contribution of edge diffraction field of nozzle outlet to the radar cross section (RCS) of S-shaped nozzle, and the IPO method was used to calculate RCS created by scattering field of cavities of S-shaped nozzle. The total RCS of S-shaped nozzle was calculated through vector summation of electromagnetic wave generated by two electromagnetic fields. On this basis, RCS characteristics of the S-shaped nozzle with three different outlet shapes were investigated. The results show that the outlet shape has great effects on RCS, and the S-shaped nozzle with circular outlet have the minimum RCS. The dislocation of sawtooth modification can effectively decrease the RCS of nozzle. The S-shaped structure of nozzle makes the RCS of the total scattering filed not symmetrically distribute about 0° detection angle within the range of global detection, which shifts the maximum RCS to the region of the positive detection angle.
Effects of secondary injection forms on thrust vector performance of shock vector controlling nozzle
SHI Jing-wei, WANG Zhan-xue, LIU Zeng-wen, ZHANG Xiao-bo
2013, 28(12): 2678-2684.
Abstract PDF(1411KB) icon1755 icon1140
Abstract:
By taking alterable specific heat ratio and effects of temperature on viscosity coefficient into account,based on CFD technology,effects of secondary injection geometric parameters,including injection angle and non-dimension slot width,on three dimensional flow characteristic and vector performance of shock vector controlling nozzle under different nozzle pressure ratios and secondary pressure ratios were investigated.Results show that,with increase of injection angle,position of main separation line before injection slot moves forward and shock angle ascends.In case of smaller secondary pressure ratio,thrust vector angle increases with the injection angle.When secondary pressure ratios equal to 1.0 and 1.2,there is an optimal injection angle for a maximal thrust vector angle.If non-dimension slot length is less than 1.0,the separation vortex before injection slot becomes into horse vortex and induces wake vortex.When secondary pressure ratio is larger than 0.6,thrust vectoring angle ascends with the increase of non-dimensional slot length.
Multiscale model for incompressible turbulent flows
DONG He, GAO Ge, LI Zhi-qiang, TANG Yang-yang, XU Huan, BAO Xing-dong
2013, 28(12): 2685-2690.
Abstract PDF(1310KB) icon1744 icon1094
Abstract:
A multiscale model based on variable interval time average method and a set of averaged equations for incompressible turbulent flows were presented.Unlike traditional turbulence models,the multiscale characteristics of turbulent flows were researved during establishment,and more accurate prediction of the flow field was given.The credibility of this model was verified through numerical simulation of the flow over a back-facing step and the flow in an asymmetric plane diffuser.The reattachment length and the surface pressure coefficient on step-side wall for the flow over a back-facing step were closer to the experimental results than the results that calculated with the standard k-ε model, which is almost 20%. The error of the position of the recirculation zone for the flow in an asymmetric plane diffuser is almost 7%, and the error of the frictional resistance coefficient on inclined wall is almost 5%, while the flow separation could not be predicted using the standard k-ε model.Results show that this model is suitable for separated flows, and gives a more accurate prediction of flow field, so this model is useful in engineering application.
Experiment of airflow induced by microsecond pulse surface dielectric barrier discharge under pressure influences
ZHOU Peng-hui, TIAN Xi-hui, CHE Xue-ke, NIE Wan-sheng, HOU Zhi-yong
2013, 28(12): 2691-2697.
Abstract PDF(1226KB) icon1517 icon982
Abstract:
Particle image velocimetry (PIV) technology was applied to obtain the evolution of the flow field induced by microsecond pulse plasma aerodynamic actuation, while the starting vortex, flow filed and wall jet were analyzed at different air pressures. Thrust created by the actuator was calculated and analyzed based on the experimental data. Experiment results showed that one starting vortex was found at the ground pressure and the pressure of 5500Pa, while two starting vortices were found at the pressure of 19000Pa and 11700Pa. The steady configuration of the flow field was complex, and evolved towards L, ∽ and V structure as the pressure decreased. The reaction time of the flow field and the tangential distance of the wall jet induced by plasma aerodynamic actuation decreased as the pressure decreased, while the normal distance of the wall jet increased. The maximum thrust also decreased as the pressure decreased, and its x coordinate became closer to the actuator.
Numerical investigation of impressible turbulent flows past airfoils
DI Ya-chao, GAO Ge, DONG He, XU Jing-lei, TANG Yang-yang, XU Huan
2013, 28(12): 2698-2702.
Abstract PDF(1284KB) icon2141 icon1333
Abstract:
The standard k-ω model and the k-ω model coupled with dispersion model were computed for turbulent flow over two airfoils, NACA 0012 and NACA 4412. The flow characteristics on the surface of the NACA 0012 airfoil were analyzed in detail under a typical Reynolds number of 2.88×106 and attack angle from 0° to 15° including pressure coefficient, lift coefficient and drag coefficient; the flow characteristics on the surface of the NACA 4412 airfoil were analyzed in detail under a typical Reynolds number of 1.52×106 and attack angle of 13.87° including the flow separation and pressure coefficient, and then compared with the experiment data. Under the same condition, the new model improved the accuracy of about 5% than the standard k-ω model when calculating the lift coefficient of NACA 0012, and improved the accuracy of about 3% than the standard k-ω model when calculating the pressure coefficient of NACA 4412. The results prove its credibility and value further more.
Effect of working fluid on heat transfer of evaporating extended meniscus in capillary channel
HUANG Xiao-ming, JIN Xin, WANG Chao, LIU Wei
2013, 28(12): 2703-2708.
Abstract PDF(1165KB) icon1250 icon1038
Abstract:
To make a better understanding of the influence of working fluid on system,an approximate analytic solution of integral evaporating heat transfer in the thin film region of meniscus was obtained by solving the mathematic model of heat and mass transfer of thin film.According to the analysis,heat and mass transfer characteristic of an evaporation meniscus for different working fluids differed a lot even in the same working condition.Among all physical parameters,the influences of the ideal evaporation mass and the latent heat were dramatic.The ideal evaporation mass can reflect the mass transfer capability of the working fluid,and the latent heat can reflect the heat transfer capability of the working fluid.Through the present work,it's learnt that system with ammonia has better transfer capability than that with methanol or pentane.
Frequency mass transfer model describeing mass transfer between fuel and air
XUE Yong, FENG Shi-yu, WANG Shu, ZHOU Yu-sui, TANG Hong-gang, LIU Wei-hua
2013, 28(12): 2709-2716.
Abstract PDF(1178KB) icon1390 icon939
Abstract:
In disregard of the classical Fick's law, frequency was used to describe the speed of mass transfer between fuel and air. A frequency mass transfer mathematic model of fuel flush inerting was proposed,which employed frequency to describe the mass transfer speed with incomparable advantages than other inerting engineering models. Frequency mass transfer model calculated results were compared with certain experimental data of Federal Aviation Administration (FAA),and the effectiveness was verified;the calculated results of frequency model and other models were also compared with A320 flight volume fraction of oxygen, showing that the frequency mass transfer model presents highest precision.Further simulation results show that increased fuel load could delay the inerting process,and frequency mass transfer model calculated result is obviously different from the calculated results of non-mass transfer and instant balancing situations when the fuel tank is nearly full.
Experiment and numerical simulation of heat transfer characteristics in turbine shroud
YU Lei, CHANG Hai-ping, HU Zheng-quan
2013, 28(12): 2717-2724.
Abstract PDF(1282KB) icon1596 icon994
Abstract:
Numerical simulation and experimental methods were used to study the heat transfer characteristics of tip clearance flow in turbine shroud cavity.The impact of tip clearance flow Reynolds,outflow ratio of the front and rear holes and tip clearance on the heat transfer characteristics were simulated.Results show that the shroud rotational speed has little effect on heat transfer coefficient;the shroud heat transfer coefficient increases with the increase of leakage flow Reynolds number;heat transfer coefficient also increases with the increase of the outflow ratio of the front and rear holes,and the impact of the ratio of the front holes is larger;heat transfer coefficient increases with decrease of the tip clearance and the mean heat coefficient,increases faster with the decrease of tip clearance.The results show excellent agreement with the measurements and simulations, the error is less than 10%.
Heat transfer enhancement characteristics of parallel-microchannel silicon heat sink with expansion-constriction cross sections
CHAI Lei, XIA Guo-dong, ZHOU Ming-zheng, CUI Zhen-zhen
2013, 28(12): 2725-2730.
Abstract PDF(1119KB) icon1569 icon906
Abstract:
With deionized water as working fluid,experiments on fluid flow and heat transfer enhancement characteristics were conducted in the parallel-microchannel silicon heat sink with expansion-constriction cross sections.Based on the microscale heat transfer enhancement mechanism,two parallel-microchannel silicon heat sink with expansion-constriction cross sections were designed and processed.In contrast to the corresponding conventional rectangular microchannel heat sink,the flow and heat transfer parameters of parallel-microchannel silicon heat sink with expansion-constriction cross sections were obtained in different volume flow rates and constant wall heat flux,along with simultaneous measurement of volume flow rate,pressure drop and temperature in the inlet and outlet,and wall temperature at the substrate of heat sink.It is found that the heat transfer rate of parallel-microchannel silicon heat sink with expansion-constriction cross sections is increased by 12.5%-85.1% over the rectangular straight microchannel heat sink value,but the friction factor is only increased by -9.2%-31.4%,showing that the parallel-microchannel silicon heat sink with expansion-constriction cross sections has superior heat transfer enhancement characteristics.
Principle experiments on two phase pulse detonation turbine engine
LI Xiao-feng, ZHENG Long-xi, QIU Hua, ZHENG Hua-lei
2013, 28(12): 2731-2736.
Abstract PDF(1033KB) icon1808 icon975
Abstract:
In order to verify the feasibility of the pulse detonation turbine engine(PDTE), a principle experiment system mainly composed of pulse detonation combustor, compressor and turbine, etc., was established. By taking gasoline as fuel and air as oxidizer, the principle experiments of PDTE were carried out. The test results show that the pulse detonation combustor, compressor and turbine can match each other successfully and the engine can stably work at the self-suction mode for a long time. The operating frequency of the engine is up to 18Hz after installation of the pneumatic valve, showing a good attenuation effect on the back propagation detonation wave. It is found that the effect of the pneumatic valve is more significant at low frequencies. When the engine works at 6Hz, the pressure wave peak attenuation is 93.8%, while at 18Hz it is reduced to 78.4%. Decreasing the back propagation pressure is conducive to the coordination between the chamber and the compressor, and at the same time it can shorten the back propagation distance, helping to improve the operating frequency of the engine.
Design of combustion chamber program of two-stroke direct injection spark ignition engine based on the CFD
ZHU Cheng, YANG Hai-qing, WANG Ming-sheng
2013, 28(12): 2737-2745.
Abstract PDF(1565KB) icon1473 icon951
Abstract:
The combustion chamber of the two-stroke engine was modified to a direct-injection combustion chamber by using 3-D entity modeling software UG, then 3-D CFD software Fluent was used to simulate and analyze the in-cylinder fluid structure. The results show that, when the height of combustion chamber is reduced to 24mm from 32mm, and the distance from the top of piston to the bottom of cylinder head is reduced to 3mm from 7mm, the roll back flow structure in the process of compression disappears, and the scavenging efficiency increases from 87% to 91%. The simulation results provide a good basis for further structure optimization of combustion chamber.
Experiment on gas ingestion on forward disk cavity of 1.5 stage turbine rig
ZHANG Ling-jun, LUO Xiang, YU Hong-peng, GUO Jun
2013, 28(12): 2746-2751.
Abstract PDF(1229KB) icon1390 icon890
Abstract:
An experimental investigation on the gas ingestion phenomenon was performed on the rig of 1.5 stage turbine with different rotating velocities and seal mass flow rates. The experimental measurements include time-average and unsteady pressure field measurements and carbon dioxide volume fraction technique. These data were used to find out the influence of the interaction between rotor blades and stator blades on the phenomenon of gas ingestion and investigate the details during the process of the main gas into the cavity. The study suggests that, some part of the pressure on the annulus out of the seal in higher than the pressure inside seal rim due to the circumferential variation following the vane pitch. And this part decreases as seal mass flow rate increases. An unsteady blade-periodic component is found in this experiment, which is also a key to ingestion. The minimum necessary value of seal mass flow rate is obtained by carbon dioxide volume fraction technique. And the fact that the path of the main gas ingestion into the disk cavity is arranged along the stator when seal mass flow rate is not enough can also be inferred.
Fault characteristics and diagnosis method of intershaft bearing in aero-engine
LIAO Ming-fu, MA Zhen-guo, LIU Yong-quan, WANG De-you
2013, 28(12): 2752-2758.
Abstract PDF(1436KB) icon1874 icon1297
Abstract:
Spectrum and envelope spectrum analysis of vibrations measured on aero-engines were developed in rotary-speed-difference-domain for detection of faults in inter-shaft bearings. Rotary-speed-difference of high pressure rotor and low pressure rotor is used as triggering signal. Vibration signals were sampled at the whole cycles of rotary-speed-difference,and their spectrum and envelope spectrum were analyzed in rotary-speed-difference-domain. The result shows that the position of vibration components caused by rotor imbalance, misalignment and defects in normal bearings(outer race fixed) will change in the horizontal coordinate(octave form in rotary-speed-difference-domain) when the rotary speed changes. However the side-band components in the vibration spectrum resulting from defects in inter-shaft bearings will keep constant space between any two components when the rotary speed changes. This phenomenon is referred to as "constant space " feature. Furthermore, vibration components in envelope spectrum caused by defects in inter-shaft bearings will keep constant location in the horizontal coordinate(octave form in rotary-speed-difference-domain) when the rotary speed changes. This phenomenon is referred to as "constant octave " feature. The experimental results obtained from the measurements on a test rig of inter-shaft bearing with defects in outer race show that the two features really present in the spectrum and envelope spectrum in in rotary-speed-difference-domain respectively.
Approach for incipient fusion fault diagnosis of rolling bearing of aero-engine based on regularized multiple kernel discriminant analysis
HAO Teng-fei, CHEN Guo, LIAO Zhong-kun, CHENG Xiao-yong, ZHAO Bin, WANG Hai-fei
2013, 28(12): 2759-2770.
Abstract PDF(2061KB) icon1784 icon930
Abstract:
To solve the problem of incipient fault diagnosis of rolling bearing of aero-engine based on the testing signal from engine case, a fusion fault diagnosis approach based on regularized multiple kernel discriminant analysis was proposed. In this method, firstly, several different types of features for the fault diagnosis of rolling bearing are extracted. Secondly, for each of these types of features, a group of kernel matrices are computed by the same set of kernel parameters respectively, then all of the kernel matrices are combined together. Finally, the optimal linear combination coefficients of the kernel matrices for the objective function of regularized kernel discriminant analysis are obtained by solving a semi-infinite linear program, then the linear combination of the kernel matrices was obtained by the combination coefficients to fuse the information of different types of features. The experimental results demonstrate that the proposed fusion fault diagnosis method can improve the accuracy of fault diagnosis about 9.25% significantly when compared with the diagnosis method using a single type of features,and can also improve the level of automation of fault diagnosis by avoiding the problem that kernel matrix must be selected manually.
Dynamic characteristics of co-rotating/counter-rotating dual-rotor system
JIANG Yun-fan, LIAO Ming-fu, LIU Yong-quan, WANG De-you, JIN Lu, LU Peng
2013, 28(12): 2771-2780.
Abstract PDF(1622KB) icon1555 icon1045
Abstract:
A dynamic model of dual-rotor was set up.The influence of inter-shaft bearing stiffness and the gyroscopic moments of high and low pressure rotors were considered in this model.The difference of co-rotating or counter-rotating dual-rotor's critical speed characteristics and unbalance response and the influence of speed ratio on co-rotating or counter-rotating dual-rotor's critical speed characteristics and unbalance response were revealed by numerical analysis and experiments.The results show that,gyroscopic moment is a main influential factor to the rotor stiffness of dual-rotor system with inter-shaft bearing,and the changes of stiffness are related to the speed ratio and the relative rotating direction of inner and outer rotors,further causing the change of co-rotating or counter-rotating dual-rotor's critical speed characteristics and unbalance response.Compared with the co-rotating dual-rotor of the same structure with the counter-rotating dual-rotor,the counter-rotating dual-rotor's unbalance response is more obvious than the co-rotating dual-rotor's under the same unbalance mass,and for this reason the unbalance mass of counter-rotating dual-rotor's inner and outer rotors should be controlled more strictly during the dynamic balance.
Analysis on bifurcation of a vibration jumping and engineering control in aero-engine rotor
CHEN Hui-zheng, CHEN Yu-shu
2013, 28(12): 2781-2789.
Abstract PDF(1685KB) icon1519 icon975
Abstract:
To investigate the problem of vibration jumping in the aero-engine with squeeze film damper,the aero-engine rotor was simplified as a rigid-rotor with elastic-support.Dynamic equations of the system were established according to the oil-film force model,which were obtained by short bearing approximation and π-film assumption.The transition set of system was obtained by averaging method and Chen-Langford (C-L) method.The parametric plane of bearing coefficient and eccentricity coefficient was divided into three different regions by the transition set.Given different characteristics of bifurcation in each region,the region Ⅰ is an ideal region without jumping phenomenon.Then,an additional structure with "soft characteristic" of nonlinearity could expand the ideal region Ⅰ,decrease the jumping interval and broaden the range of optimization parameter selection.
Effect of constant maneuver load on vibration characteristics of aero-engine’s rotor system
HOU Lei, CHEN Yu-shu
2013, 28(12): 2790-2796.
Abstract PDF(1603KB) icon1492 icon1227
Abstract:
An asymmetric placed Jeffcott rotor system with nonlinear elastic support was considered,and the influences of constant maneuver load on the dynamics of the rotor system were studied numerically.By setting different constant maneuver loads,it was found that the relationship between the amplitude and the excitation frequency may lead to different phenomenons including:hysteresis region narrowing,disappearance and secondary jump.With the variation of the frequency ratio,the relationship between the amplitude and the constant maneuver load is changed significantly.Under certain excitation frequency,if the constant maneuver load crosses a critical value,the amplitude of the system can jump from a small level to a large one,and not drop down even though the load is reduced to zero.In addition,the offset of the rotor's axis is not closely related to the excitation frequency,but mainly depended on the amount of the constant maneuver load.
Efficient fault identification method for dual rotor-supporting system using model-based method
CHEN Jing-ming, JIANG Dong-xiang, XU Hong-zhi
2013, 28(12): 2797-2802.
Abstract PDF(1027KB) icon1418 icon1091
Abstract:
The finite element model of dual rotor-supporting system was constructed.Based on the finite element model,vibration signal under the faults of mass unbalance and local shaft bow was simulated.A model-based method was developed to identify the fault in the dual rotor-supporting system.1-fault search method,2-fault search method and 3-fault search method were utilized to identify the fault efficiently and accurately.The validation results show that the method could identify single fault and multi-concurrent faults accurately and confirm the fault location,severity and phase simultaneously.This method optimizes fault search process,which is used to decreases 98.9% calculation amount in the ideal situation,and accelerates fault identification.Besides,if comparing with the identification results by adding different adding noises,the relative error is around 1% which validates good robustness to noise.
Large-eddy simulation of separated boundary layer transition in low-pressure turbine cascade with and without wakes
LIU Zhi-gang, YE Jian, ZOU Zheng-ping
2013, 28(12): 2803-2812.
Abstract PDF(1972KB) icon2135 icon1075
Abstract:
A well validated large-eddy simulation (LES) solver for compressible flows was employed to simulate the low pressure turbine (LPT) cascade T106D-EIZ where the Reynolds number and Mach number were 60154 and 0.402,respectively. Two cases with steady inflow and periodic wakes inflow were calculated and analyzed. The results of steady inflow case show that large separation bubble appears at the rear part of the blade suction surface and transition process of the separated shear layer is dominated by Kelvin-Helmholtz (K-H) instability. In the wakes inflow case, due to the periodic sweeping of inflow wakes, the size of time mean separation bubble significantly reduces and the total pressure loss of the cascade also decreases. The analysis of phase averaged and instantaneous flowfield reveals that the negative jet of wake-induced forces the separation point to move forward and then the roll-up vortex emerges. The strong interactions of sweeping negative jet and roll-up vortex result in large aerodynamic losses. Then roll-up vortex quickly breakdowns and boundary layer transitions to turbulence.
Total pressure averaging method in rotor wake of transonic axial compressor
WANG Si-chen, LIN Feng, Scott C. Morris, Joshua Cameron, NIE Chao-qun
2013, 28(12): 2813-2820.
Abstract PDF(1249KB) icon1302 icon956
Abstract:
Numerical simulation and experimental measurements were conducted to investigate the rotor wake of a transonic axial compressor. Combined with theoretical analysis, the relations between area-average total pressure and mass-average total pressure that are commonly calculated in transonic rotor wake flow fields were studied. The results showed that the area-average total pressures were larger than the mass-average total pressures at surfaces close to rotor trailing edge because of the existence of the wake flow, which had higher total pressure and lower axial velocity than the main flow. However, the downstream area-average total pressure changed to become smaller than the mass-average total pressure as the wake dissipated under the interaction with the main flow. These results can provide some references for investigations on the compressor rotor wakes, especially during comparative analysis of computational and experimental results.
Numerical investigations on unsteady flow field at tip region in transonic compressor rotor
FU Lei, SONG Xi-zhen, YUAN Wei, ZHOU Sheng, LU Li-peng
2013, 28(12): 2821-2828.
Abstract PDF(1478KB) icon1544 icon1008
Abstract:
Time-accurate simulations were performed to investigate the unsteady flow field at the tip region of a high-loading transonic axial compressor rotor at 98% design rotating speed. The results show that the oscillation of the shock is weak and the unsteadiness at the tip region is originated from the breakdown of tip leakage vortex and the shock/vortex interaction. The characteristics of tip leakage vortex were compared between design condition and near-stall condition. Detailed analysis was then made to emphasize the development of the behavior of tip leakage vortex at near-stall condition, where leading-edge spillage occurred intermittently. The breakdown of the tip leakage vortex after the shock contributes to a large blockage and also the stall disturbance of spike type.
Aerodynamic optimization of wind turbine with optimal circulation distribution based on full free vortex wake model
SONG Xian-cheng, CHEN Jiang, DU Gang, CAO Ren-jing
2013, 28(12): 2829-2835.
Abstract PDF(1229KB) icon2388 icon1131
Abstract:
Through optimization of the blade bound circulation distribution, a fast aerodynamic optimization method for blade of wind turbine was developed. In the method, the full free vortex wake model was introduced, and then computed quickly by parallel processing and fast multipole method(FMM). When selecting Fourier series representation of the bound circulation as the optimization variables to decrease the number of optimization variables, using the power coefficient as an objective function and adding the thrust coefficient as a constraint, optimization was carried out and optimal blade geometry parameters were obtained from optimal circulation distribution. This was validated through comparisons with the National Renewable Energy Laboratory (NREL) experimental rotor. Results show that, when tip speed ratio was 3.79 and 4.74, with a thrust coefficient constraint, optimization could enhance the power coefficient by 32% and 8%, respectively. When a variety of blade numbers and tip speed ratios were chosen, without a thrust constraint, global optimizations were performed, and the power coefficients are over 0.48.
Aero-engine power control based on life consumption of ligh pressure turbine blade
LIU Bao-hua, HUANG Jin-quan
2013, 28(12): 2836-2841.
Abstract PDF(1028KB) icon1427 icon1011
Abstract:
Engine rating control strategy based on the life consumption of high pressure turbine (HPT) blade was put forward.The thrust requirement temperatures of HPT blade in various environments were obtained by flight mission simulation using aircraft and engine models.Reverse engineering method was used to calculate the life consumption of HPT blade.Results show that the control strategy of reducing HPT blade' temperature can significantly cut down the life consumption of HPT blade in various conditions while meeting the thrust requirement.It verifies that the life consumption calculation method of HPT blade is simple and feasible.By continuously adjusting the engine HPT environment temperature approaching the thrust requirements baseline,the service life of the engine could be effectively extended.Results state that the engine rating control based on the life consumption of HPT blade is effective to reduce the engine life cycle cost,playing a significant role for civil aviation engine control and operation.
Coordinated control of dual-channel flow-rate for fuel supply system of high-speed heat-airflow wind tunnel
CAI Chao-zhi, LI Yun-hua, TENG Feng-jian, DONG Su-jun
2013, 28(12): 2842-2848.
Abstract PDF(1279KB) icon1226 icon824
Abstract:
In order to solve the coordinated control problem of dual-channel flow-rate in the fuel supply system of the high-speed heat-airflow wind tunnel,a coordinated controller of dual-channel flow-rate based on the cross coupling control algorithm and deriving the virtues of the sliding mode variable-structure control method and dynamic matrix predictive control was developed. Simulation results illustrate that the single-channel flow-rate controller is able to achieve a fast, no overshoot and precise control of the flow-rate, adjustment time is about 10 seconds, and the control accuracy is 0.1%, and has the ability to overcome the time delay; the coordinated controller improves the dynamic track-ability of dual-channel flow-rate and the tracking error within ± 0.1L/min.
Microwave attenuation in vacuum plume of the liquid-propellant rocket engine
WANG Hong-yue, TANG Zhen-yu, HE Bi-jiao, CAI Guo-biao
2013, 28(12): 2849-2856.
Abstract PDF(1219KB) icon1425 icon930
Abstract:
The microwave attenuation in the vacuum plume of the liquid-propellant rocket engine was studied. Based on a sample of the bipropellant engine, the electron number densities in the chamber was calculated using a thermodynamic calculation code. The ionization and recombination processes in the nozzle were simulated under the assumption of frozen components or limited reaction rate. The electron number densities in the plume and the microwave attenuation of 5－30GHz were estimated. It is shown that the number densities are within the range of 1013-1014cm-3 and 1010-1011cm-3, respectively, for the chamber and the exit of the nozzle. The alkali metals, K and Na, are main contributors of electrons while Cl- and OH- are main electron absorber. The attenuation is more serious for the microwave of lower frequency and oblique path, as high as 4.5dB in case of 5 GHz.

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