OUTFLOW BOUNDARY CONDITION IN THE FINITE-VOLUME METHOD FOR UNSTEADY-STATE FLUID FLOW COMPUTATION WITH VARIABLE DENSITY

This paper presents the outflow boundary condition for unsteady-state fluid flow computations with variable density as part of the semi-implicit method for pressure-linked equations (SIMPLE) calculation in the finite-volume method. In the SIMPLE algorithm, there is no built-in numerical procedure to calculate the velocities at an outflow boundary. The outflow boundary condition is meant to satisfy the mass flow rate between the inflow and outflow boundary conditions and the sum of all transient terms over the entire computational domain. When the proposed outflow boundary condition for unsteady-state computations is applied to a thermal fluid flow calculation, stable, robust, and highly accurate mass conservation is obtained compared with that obtained for steady-state calculations. Therefore, the proposed outflow boundary condition is expected to have wide applicability in unsteady-state fluid flow computations with variable density, such as in combustion calculations.