Abstract
We present numerical tests of outflow boundary conditions at an open boundary for simulations of vortex flows. The Sommerfeld radiation condition is convenient for finite difference methods and often used. However it is not clear which value of the convective velocity is appropriate. We compare four different convective velocities, which are mean velocity at exit boundary, arithmetic mean velocity of maximum and minimum value at exit boundary, local instantaneous velocity, and calculated velocity from Orlanski's formulation. The test cases for boundary conditions evaluation are double Lamb dipole vortices convecting in week uniform flow, and a two-dimensional jet flow. The Orlanski's method yield little reflection and is recommended for use at open boundary.
