Investigation of boundary conditions for computational aero acoustics

For most aeroacoustics problems, the spatial domain is unbounded. Therefore, the need for artificial boundary conditions arises in order to make the computational domain finite. The artificial boundary conditions should be such that the numerical boundaries are transparent to all out-going waves while preventing the entrance of nonphysical waves. It has been established over the last few years that the accuracy requirements of the boundary conditions as well as the solution schemes are much more stringent for aeroacoustics problems. In this paper, the effectiveness of various artificial boundary conditions for computational aeroacoustics is examined. It is shown that among all the numerical boundary conditions, the PML boundary conditions simulate the far field almost perfectly. Most of the earlier work in PML has been carried out over uniform grids using Cartesian coordinates. However, most practical problems are seldom confined to uniform grids. Thus in this paper, the PML boundary conditions are extended to the generalized coordinates. Numerical examples are presented to demonstrate the validation of the proposed PML boundary conditions in the generalized coordinates.