A Nonreflecting Outflow Boundary Condition for Subsonic Navier-Stokes Calculations

A nonreflecting boundary condition is presented for the numerical solution of the time-dependent compressible Navier-Stokes equations when these equations are used to obtain a steady state. This boundary condition is shown to be effective in reducing reflections at a subsonic outflow boundary. Numerical calculations using a model problem were made to compare this boundary condition with other outflow boundary conditions. The non-reflecting boundary condition contains a parameter whose optimal value is estimated using the analysis of a simplified set of equations.