INFLOW AND OUTFLOW BOUNDARY-CONDITIONS FOR DIRECT NUMERICAL SIMULATIONS

New inflow and outflow boundary conditions are proposed. These conditi ons are applied to two test problems. One is a problem in which a vort ex convected by a uniform mean flow passes through an outflow boundary . The other is a two-dimensional spatially developing mixing layer. Th e new boundary conditions which give highly accurate results for both test problems consist of convective-viscous conditions and an approxim ate transport equation for pressure. The applicability of the convecti ve-viscous conditions is verified by numerical tests which show that c onventional boundary conditions do not approximate the velocity or the pressure fields on the boundary. The pressure transport equation prop osed in this work is used to obtain the pressure on the inflow and out flow boundaries from a previous time step pressure field. As a result, we can conclude that the new boundary conditions are appropriate for direct numerical simulations of spatially developing flows.