抄録
In the unsteady incompressible flow simulation using the Navier-Stokes equations expressed by the vorticity and the streamfunction, a Sommerfeld radiation condition is adopted for the open boundary condition, i.e., the outflow condition. Two types of determination of the phase velocity are presented, that is, the phase velocity is calculated numerically and fixed by the uniform velocity. In the simulation of the flow past a cylinder, two Sommerfeld radiation conditions are compared with the usual one-side finite difference condition, i.e., the extrapolation. When the computational region is sufficiently long in the wake direction, the results obtained by the above three conditions are in good agreement with each other. When the region is short, the Sommerfeld condition with the calculated phase velocity is the most suitable condition among them.
