A Method Of Preconditioning For Reducing The Affection Of Large Aspect Ratio And Stagnation

When using time marching scheme to resolve steady flow in low-speed, Low conversation and accuracy so-called stiffness are common,Preconditioning is effective technique to overcome stiffness, so it is a focus in CFD research domain.Firstly according to the production which get in our lab, we using the Van Leer preconditioner and MUSCL scheme achieve the three-dimension arithmetic of preconditioning. And we append it to the software which called NAPA. At last we apply preconditioning technique to some simple external or internal flow. The interation is decrease to 1/10 in low-speed or transonic flow.Through these experiments, it proves that the Euler preconditioning can accelerate the convergence and improve accuracy in the low-speed flow, which enhances the performance of Euler time marching schemes in this areas.Secondly we study the Euler preconditioners with regard to various design criteria formulated for enhancing the performance of Euler time-marching schemes in the areas of efficiency, accuracy, and robustness. Especially care for the influence on the robustness about eigenvecotrs of the coefficient matrix. We find that the stagnation preconditioner is better when computing the low-speed flow.Thirdly we show the technical background of the stretched cells and the stagnation preconditioners. And apply them to the numerical implementation of wave speeds and stability analysis. It proves that the stagnation preconditioning advantages the speed of convergence dealing with the large aspect ratio models in the low speed.Finally we programme combines Van Leer and stagnation preconditioning which is better than using single preconditioning.