On absorbing boundary conditions for linearized Euler equations by a perfectly matched layer

Recently, Berenger introduced a perfectly matched layer (PML) technique for absorbing electromagnetic waves. In the present paper, a perfectly matched layer is proposed for absorbing out-going two-dimensional waves in a uniform mean flow, governed by linearized Euler equations. It is well known that the linearized Euler equations support acoustic waves, which travel with the speed of sound relative to the mean flow, and vorticity and entropy waves, which travel with the mean flow. The PML equations to be used at a region adjacent to the artificial boundary for absorbing these linear waves are defined. Plane wave solutions to the PML equations are developed and wave propagation and absorption properties are given. It is shown that the theoretical reflection coefficients at an interface between the Euler and PML domains are zero, independent of the angle of incidence and frequency of the waves. As such, the present study points out a possible alternative approach for absorbing outgoing waves of the Euler equations with little or no reflection. In actual computations, nonetheless, numerical reflection will still occur due to discretization and mesh truncation, depending on the thickness of the PML domains and absorption coefficients used. Numerical examples that demonstrate the validity of the proposed PML equations are presented. (C) 1996 Academic Press, Inc.