低速湍流模拟的预处理技术研究

本文开展低速湍流的预处理技术研究. 该预处理技术采用守恒型变量及主控方程与湍流方程相耦合的隐式求解方法, 并为确保迭代求解稳定性, 发展了合理的参考马赫数定义、双时间步无矩阵方法迭代求解形式以及湍流源项隐式处理方法等, 从而真正实现全速湍流软件平台统一形式. 在喷管、翼型和方柱等低速湍流数值模拟中, 本文方法正确刻画了流场结构特征, 计算与理论、实验等相关结果符合较好, 具有很强的迭代收敛性和结果精度.

Study of precondition for simulating low-speed turbulence

Precondition for simulating low-speed turbulence is studied in this paper. Against the stiffness of the time-dependent scheme applied to low-speed turbulence, the precondition based on conservative variables is developed, which adopts an implicit iterative method for solving main control equations coupled with turbulence transport equations. In order to ensure the iterative solution stable, a reference Mach number, the dual-time stepping no-matrix scheme, and the method for processing implicitly the source terms of turbulence equations etc. have been developed reasonably, making the software platform unified for all-speed turbulence. Reference Mach number is defined in terms of global and local velocity by a single parameter, and the parameter can be used to control stability, numerical result accuracy, and switch of the precondition. The dual-time stepping LU-SGS method based on conservative variable precondition is developed, realizing no-matrix iterative solution for unsteady flow problems. Against the stiffness in solving the main control equations coupled with turbulence transport equations, the dissipation term of the turbulence equations is processed implicitly, which can enhance main diagonal dominance of the turbulence equations and make the iteration with greater stability. In simulating the turbulence in a nozzle and around a square cylinder or an airfoil, the precondition depicts correctly the structural character of the flowfield; and the computational results are in good agreement with those of theory and experiment etc., and its iterative convergence and numerical accuracy is excellent. It is shown that the precondition in this paper for low-speed turbulence is very effective.