MmB DIFFERENCE SCHEMES FOR TWODIMENSIONAL HYPERBOLIC CONSERVATION LAWS

A new class of second order accuracy semidiscrete difference schemes is presented for the two-dimensional nonlinear scalar hyperbolic conservation laws. It is based on flux splitting, piecewise linear cell-averaged reconstruction and upwind property in the spatial discretization. By using TVD Runge-Kutta time discretization method, the full discrete scheme is obtained and its MmB property is proved. The extension to the two-dimensionalnonlinear hyperbolic conservation law systems is straightforward by using component-wise manner. The main advantage is simple: no Riemann problem is solved, and so field-by-field decomposition is avoided and the complicated computation is reduced. Numerical results of two-dimensional Euler equations of compressible gas dynamics verify the accuracy and robustness of the method.     

3D NUMERICAL SOLUTION OF AERO-NOISE WITH HIGH-ORDER DISCONTINUOUS GALERKIN METHOD

The flow-induced noise is simulated with a hybrid method. Firstly, a steady-state background flow field is given by solving Reynolds averaged Navier-Stokes（RANS） equations with finite volume （FV） method on struc- tured grid. Then the linearized Euler equations（LEE） can be constructed based on the resulted background flow field, where the source term on the right hand side is computed using stochastic noise generation and radiation （SNGR） method, Finally, the unsteady acoustic field is obtained through solving LEE using high-order discontinu- ous Galerkin（DG） method on unstructured grid, where the parallel computing based on mesh partitioning and a ＂Quadrature-Free Implementation＂ method for high-order DG are employed to accelerate the computation. In order to demonstrate the sound propagation in detail, a visualization method for high-order schemes is also developed here. Moreover, in order to test the validation and the accuracy, a 3D cavity test in comparison with the experi- mental data is displayed first in this paper, then a 3D high-lift wing is also simulated to demonstrate its capability for very complex geometries.     

Performance of Cross-Layer Design with Power Allocation in Space-Time Coded MIMO Systems

A cross-layer design（CLD）scheme with combination of power allocation,adaptive modulation（AM）and automatic repeat request（ARQ）is presented for space-time coded MIMO system under imperfect feedback,and the corresponding system performance is investigated in a Rayleigh fading channel.Based on imperfect feedback information,a suboptimal power allocation（PA）scheme is derived to maximize the average spectral efficiency（SE）of the system.The scheme is based on a so-called compressed SNR criterion,and has a closed-form expression for positive power allocation,thus being computationally efficient.Moreover,it can improve SE of the presented CLD.Besides,due to better approximation,it obtains the performance close to the existing optimal approach which requires numerical search.Simulation results show that the proposed CLD with PA can achieve higher SE than the conventional CLD with equal power allocation scheme,and has almost the same performance as CLD with optimal PA.However,it has lower calculation complexity.     

ROBUST REPETITIVE CONTROL FOR IMPROVING RATE SMOOTHNESS OF TEST TURNTABLE

A robust repetitive control scheme is used to improve the rate smoothness of a brushless DC motor (BLDCM) driven test turntable. The method synthesizes variable structure control (VSC) laws and repetitive control (RC) laws in a complementary manner. The VSC strategy can stabilize the system and suppress uncertainties, such as the aperiodic disturbance and noises, while RC strategy can eliminate the periodic rate fluctuation in a steady state. The convergence of the repetitive learning process is also guaranteed by VSC. A general nonlinear system model is discussed. The model can be considered as an extension of BLDCMs. The stability and asymptotic position tracking performance are validated by using Lyapunov functions. Simulation results show the effectiveness of the proposed approach for improving the rate smoothness.     

CONSERVATIVE FRONT TRACKING IN HIGHER SPACE DIMENSIONS

INTRODUCTIONWe propose and demonstrate a tracking fi-nite difference algorithm which is( a) fully con-servative and ( b) improves local truncation errorby one order( from O( 1 ) to O( Δx) near trackeddiscontinuities.Discontinuities in the solutions of systems ofnonlinear hyperbolic conservation laws are widelyrecognized as a primary difficulty for numericalsimulation.Surprisingly,the nonlinearities actu-ally help,as they cause information,which flowsalong solution characteristics,to flow…     

WAKE GEOMETRY CALCULATIONS FOR TILT-ROTOR USING VISCOUS VORTEX METHOD

A tilt-rotor unsteady flow analytical method has been developed based upon viscous vortex-particle meth- od. In this method, the vorticity field is divided into small assembled vortex particles. Vortex motion and diffusion are obtained by solving the velocity-vorticity-formed incompressible Navier-Stokes equations using a grid-free La- grangian simulation method. Generation of the newly vortex particles is calculated by using the Weissinger-L lifting surface model. Furthermore, in order to significantly improve computational efficiency, a fast multiple method （FMM） is introduced into the calculation of induced velocity and its gradient. Finally, the joint vertical experimen- tal （JVX） tilt-rotor is taken as numerical examples to analyze. The wake geometry and downwash are investigated for both hover and airplane modes. The proposed method for tilt-rotor flow analysis is verified by comparing its re- sults with those available measured data. Comparison indicates that the current method can accurately capture the complicated tilt-rotor wake variation and be suitable for aerodynamic interaction simulation in complex environ- ments. Additionally, the aerodynamic interactional characteristics of dual-rotor wake are discussed in different ro- tor distance. Results show that there are significant differences on interactional characteristics between hover mode and airplane mode.     

NEW APPROACHES OF MUSCL SCHEMES FOR COMPRESSIBLE FLUIDS

The MUSCL scheme for compressible gas dynamicsis studied in this paper. We propose a new type of Euleri-an MUSCL scheme, which evaluates the intercell flux athalf time step. The intercell flux is comptuted from char-acteristic equations with the data which traced backthrough the approximatecharacteristic from the edge athalf time step. The data is classified in several differenttypes, depending on the characteristic directions of data.We also present a general procedure of oscillation-fre…     

DEVELOPMENT AND APPLICATIONS OF WENO SCHEMES IN CONTINUUM PHYSICS

INTRODUCTIONHigh order accurate weighted essentiallynon- oscillatory( WENO) schemes have been de-veloped to solve a hyperbolic conservation lawut+ .f( u) =0 ( 1 )The first WENO scheme was constructed in Ref.[1 ]for a third order finite volume version in onespace dimension.In Ref.[2 ],third and fifth or-der finite difference WENO schemes in multiplespace dimensions are constructed,with a generalframework for the design of the smoothness indi-cators and nonlinear weights.L ater,second…     

HIGH TEMPERATURE RHEOLOGICAL BEHAVIOR OF FSJ JOINTED REGION FOR 7022ALUMINUM ALLOY

The Hopkinson pressure bar tests for base metal and friction stir jointing（FSJ） jointed region of 7022 a- luminum alloy are carried out at different temperatures and strain rates. The temperature is 30--400 ℃ and the strain rate is 1 200-5 000 s 1. High strain rate for base metal and FSJ jointed region of 7022 aluminum alloy are studied. The corresponding stress-strain curves are obtained. The results show that the flow stresses of base metal and FSJ jointed region of 7022 aluminum alloy decline with the increase of temperature and increase with the in- crease of strain rate. Furthermore, the constitutive equation for base metal and FSJ jointed region of 7022 alumi- num alloy at high temperature and high strain rate is obtained based on Johnson-Cook model.     

Experiment on Adiabatic Film Cooling Effectiveness in Front Zone of Effusion Cooling Configuration

Experimental investigation is performed to investigate the cooling characteristics in the front zone of effusion configuration. Effects of blowing ratio, multi-hole arrangement mode, hole-to-hole pitch and jet orientation angle on the adiabatic film cooling effectiveness are concentrated on. The results show that the film layer displays an obvious ＂developing＂ feature in the front zone of effusion cooling scheme, for either the staggered or inline multi-hole arrangement. The varying gradient of the laterally-averaged adiabatic cooling effectiveness along the streamwise direction is greater for the staggered arrangement than that for the inline arrangement. The holes array arranged in staggered mode with small hole-to-hole pitches is in favor of obtaining developed film coverage layer rapidly.