We discuss artificial boundary conditions for stationary Navier-Stokes flows
past bodies in the half-plane, for a range of low Reynolds numbers. When
truncating the half-plane to a finite domain for numerical purposes, artificial
boundaries appear. We present an explicit Dirichlet condition for the velocity
at these boundaries in terms of an asymptotic expansion for the solution to the
problem. We show a substantial increase in accuracy of the computed values for
drag and lift when compared with results for traditional boundary conditions.
We also analyze the qualitative behavior of the solutions in terms of the
streamlines of the flow. The new boundary conditions are universal in the sense
that they depend on a given body only through one constant, which can be
determined in a feed-back loop as part of the solution process
