预处理法求解定常/非定常混合网格的全速流场

运用时间导数预处理法在混合网格上求解三维定常/非定常N-S方程。预处理后的N-S方程,用二阶迎风格式的有限体积法离散,隐式、LU-SGS迭代求解,双时间步推进求解非定常流。本文以一维预处理欧拉方程为基础进行分析,提出了一种特征变量的边界条件以适应预处理后的特征系统。从极低速到跨声速范围的众多算例表明,本文的边界条件处理稳定有效,预处理法在各种速度下都具备同样快速的收敛性,在较宽的使用范围内均能得到理想的计算结果。

Using preconditioning method to simulate steady/unsteady flows at all speeds on hybrid grids

A time-derivative preconditioning algorithm is implemented to solve three-dimensional steady/unsteady Navier-Stokes equations on hybrid grids.The preconditioned Navier-Stokes equations are discretized by an implicit secondorder upwind finite-volume scheme and solved by applying LU-SGS method.A dual-time stepping approach extends thisalgorithm to unsteady flows.In this paper characteristic variable boundary conditions are developed to suit with the preconditioned characteristic systems.Results obtained for a wide range of Mach numbers from very low speed flows to transonic flows demonstrate that the preconditioning method ensures same rapid convergence for flows even at very low speed and also indicate that this algorithm provides satisfactory accuracy for a wide range of flow problems.