应用隐式SMAC格式计算射流放水阀内部非定常不可压粘性流场

为了分析射流放水阀内部的非定常不可压粘性流场，在一般曲线坐标系下求解了以逆变速度为参数的不可压Ｎ－Ｓ方程和压力椭圆方程。计算采用了基于隐式ＳＭＡＣ格式的有限差分格式。在这种格式中，非定常流场的速度是通过使用Ｃｒａｎｋ－Ｎｉｃｈｏｌｓｏｎ格式，并在每一时间步处以牛顿迭代的方法得到的；而压力椭圆方程是通过使用Ｔｓｃｈｅｂｙｓｃｈｅｆｆ ＳＬＯＲ格式并交替改变计算方向而求解。通过使用交错网格和迎风差分，诸如改进的ＱＵＩＣＫ格式；计算过程中的误差和数值不稳定能够得到有效地控制。计算结果和实验观察得到的流动图谱对比表明，二者十分吻合。

COMPUTATION OF UNSTEADY INCOMPRESSIBLE VISCOUS FLOW AROUND A HOLLOW-JET VALVE BY USING A IMPLICIT SMAC SCHEME

To numerically analyze the unsteady incompressible viscous flow around a hollow-jet valve, the incompressible Navier-Stokes equations of contravariant velocities and the elliptic pressure equation in general curvilinear coodinates are solved by a finite-difference method based on the SMAC (simplified Marker and Cell) scheme. In this scheme, with application of the Crank-Nicholson scheme, unsteady flow is calculated iteratively by the Newton method at each time step, and the elliptic pressure equation is solved by the Tschebyscheff SLOR method with alternating the staggered grid and upstream differences, such as the modified QUICK scheme, sparious error and numerical instabilities can be suppressed. The calculated flow patterns are in good agreement with those obtained by high- speed photographs. The computation results show that the flow field behind the valve needle can be divided into three regions, that is, a main flow region, a sheer layer region and a weak vortex region. Reynolds number and a valve opening are two factors which effected the unsteady characteristics of the flow field.