Deterministic period mean flow boundary condition for unsteady flow predictions

Abstract

The boundary conditions for an unsteady time-marching flow solver are used to specify the particular flow problem of interest. Often, the boundaries of the computational domain are located in the flow itself, artificially truncating the physical flow problem. Such ‘free’ boundary conditions must allow outgoing disturbances to exit the computational domain without generating spurious nonphysical reflections, while simultaneously maintaining the desired mean flow conditions and imposing any unsteady incoming disturbances. In this work, a new Deterministic Period Mean Flow Boundary Condition (DP-MFBC) method for accurately and efficiently obtaining the desired time-averaged mean flow at these computational boundaries is presented. The DP-MFBC method is designed to be used in combination with existing nonreflecting boundary conditions, and establishes and maintains the desired mean flow without introducing additional spurious reflections of the outgoing disturbances. Results for the DP-MFBC method are shown for representative model problems and compared to previous approaches.