The Application Of Fringe Method As The Outflow Boundary Condition For The Direct Numerical Simulation Of Compressible Flows

Direct numerical simulation is an effective method to study fluid flows. Becausethe computational domain is always smaller than the domain of real flows, appropriateboundary conditions should be applied to enssure the correctness of the computationalresults. For the numerical simulation of compressible flows, characteristic boundaryconditions are often being used to ensure that the disturbances can pass through theboundary without causing reflections. However, sometimes, they do not yieldsatisfactory results for unsteady flows. On the other hand, "fringe method", also called "buffer zone method", has beenproved to be effective in guarantee non-reflection for incompressible flows. Its mainidea is that a fringe, or buffer zone, is added to the original computational domain, inwhich the governing equations are modified, such that disturbances are almost totallydamped in propagating through this buffer zone, so there will be no disturbance to bereflected at the exit of the buffer zone. In this paper, by applying the "fringe method"to several unsteady compressible flows, such as the evolution of disturbances insubsonic and supersonic boundary layers, vortex convection in a supersonic flow, andthe scattering of T-S waves at the trailing edge of a subsonic boundary layers on a flatplate, we showed that the fringe method is also effective for compressible flows. Wehave proposed a criterion for the effectiveness of the method, and also discussed theeffects of the parameters in the fringe method.