Boundary conditions at inflow and outflow planes

The problem of analyzing complex flows in infinite domains by replacing the infinite region by a bounded region is examined. The formulation of appropriate boundary conditions at inflow and outflow planes is discussed, and methods of verifying that the solution to the finite problem represents a valid approximation to the solution of the infinite problem are evaluated. A model problem for the creeping flow of a Newtonian fluid is solved, and it is shown that utilization of a finite domain leads to some inaccuracies in the evaluation of pressure gradients and pressure drops. It is further shown for the model problem that it is possible to obtain seemingly acceptable solutions for the finite flow field which are, in reality, poor approximations to the solution of the infinite problem.