DAE的Runge-Kutta方法在不可压NS方程求解中的应用

1．引言自然界中的流场通常是非定常复杂流场，要正确模拟和跟踪复杂流场的变化，计算格式的时间精度极为重要．对于常微分方程（＊＊q，一般采用＊K方法及线性多步法来提高格式的时间精度．前者是单步法，在计算过程中可以改变步长，可找到稳定性较好的高精度格式：近年来在发展到偏微分方程的数倩水解中也有很多应用．原始变量的INS方程（二维）为：其中u，v分别是x，y方向速度分量，r是压力，连续方程（1．幻可视为约束条件．从［1］，［2］可见，经空间差分化后（固定空间网格），它可看作带约束的微分方程组，即微分代数方程（DAE－…

THE RUNGE-KUTTA METHODS OF DAE IN THE NUMERICAL SOLUTION OF THE INCOMPRESSIBLE NS EQUATIONS

The incompressible Navier-Stokes (INS) equations upon discretization on fixed meshes become a system of differential algebraic equations (DAE) of index 2. It is proved in this paper that for the general explicit and implicit Runge-Kutta (RK)methods, the time accuracy of velocity is the same as that for the ordinary differential equations, by taking into consideration of the special form of the resulting DAE; (the time accuracy of pressure can be lower). For the three-stage secondorder explicit RK method, algorithms with less (than three) Poisson solutions of pressure are proposed and verified by numerical experiments. However, in practical computation of complex flows it is found that the method must satisfy the so-called consistency condition for the components of the solution (here the velocity and the pressure) of the DAE for the method to be robust.