Large Eddy Simulation Based On The Computational Method Of Compressible Flows And Its Application To Engineering

On applying large eddy simulation (LES) to practical interest, the main difficulties were high requirement of numerical schemes and huge computational cost. In order to overcome the difficulties, a lot of theoretical researches were done and a code was developed with improved schemes and accelerated methods. Then, LES was applied to the computation of highly loaded turbine cascades and satisfied results were achieved.MILES approach that replaced subgrid scale model by the intrinsic dissipation of preserving monotone schemes was accepted in the paper. Then, the possibility applied to LES of adapted schemes such as Harten-TVD scheme and MUSCL-TVD scheme was researched. The deficiency of Harten-TVD scheme that was the unwanted geometrical factor in corrected flux was pointed out and a modified method in view of geometry that could improve the accuracy with irregular and uneven grid was given.It is necessary for LES to simulate low speed areas such as boundary layer. Then, the preconditioning method was used to modify the above TVD schemes for the simulation of low speed flows. The eigenvalues and eigenvectors of preconditioned system were deduced in three dimension curvilinear coordinates and the preconditioned Harten-TVD scheme and preconditioned MUSCL-TVD scheme that were good for computation of low speed Euler flows were achieved.However, the accuracy of preconditioned schemes was not satisfied because of the poor performance of stability of preconditioning techniques used in viscous flows. It was due to the unsteady structure in eigenvectors. With two assumptions of low speed flows, the new scheme named low-speed Roe scheme without the unsteady structure was deduced. The result of computation showed that low-speedRoe scheme was more adapt to MILES than classical preconditioned schemes with condition of low speed flows.In order to reduce time consuming of computation, some accelerated techniques were studied such as parallel, implicit method of DP-LUR and dual time stepped method. Incorporated with preconditioning method, DP-LUR method was upgraded as PDP-LUR method that had higher convergence rate in low speed flows.Using above methods based on the computational method of compressible flows and some other programming techniques, a parallel unsteady code named HPPD of three dimensions was developed on my own.With the code of HPPD, the LES simulation of classical high-loaded turbine blade T106 was achieved with acceptable time cost. The laminar separation, transition and turbulent reattachment were predicted accurately and unsteady phenomena of laminar bubble were analyzed.