EFFECTS OF OPEN BOUNDARY ON INCOMPRESSIBLE NAVIER-STOKES FLOW COMPUTATION: NUMERICAL EXPERIMENTS

Abstract

The issue of the acceptable numerical treatment along downstream open boundaries for incompressible flow calculations is investigated. The conventional viewpoint holds that the flow problem is not well posed when both inflow and outflow appear on open boundaries. To test this point, a series of Navier-Stokes flow calculations have been conducted for both a planar channel with a one-sided asymmetric expansion and a planar channel with a two-sided symmetric expansion with varying Reynolds numbers and grid densities. Several interesting results have been observed that are not consistent with the conventional viewpoint. The numerical experiments indicate that even with inflow across some portions of an open boundary, the numerical procedure can be well posed by adopting the straightforward extrapolation formula on the open boundary. Overall, it appears that the numerical stability of the computation is related to the Reynolds number, especially for flows with multiple recirculating eddies across the open boun...