Boundary element solutions for acoustic wave propagation in media with nonuniform flow

The interaction between acoustic wave propagation and a fluid in motion can be described by a system of coupled equations. For many applications like ultrasound flowmeters, medical ultrasound diagnostics, environmental acoustics or air conditioning systems, the influence of the acoustic waves upon the flow can be neglected. This allows a separation and therefore a successive solution of the problem. The results of finite element (FEM) simulations based on a modified wave equation with the flow profile as a boundary condition have been previously presented. In this paper, a new boundary element (BEM) technique is reported to solve this problem. One major advantage over FEM is the reduced dimension of the problem, leading to easier meshing and, especially for unbounded domains, to reduced computational effort. For the new BEM approach the Green's function had to be modified to consider flow. Based on an approximate Green's function a boundary element solution was developed. This new approach is compared with the previously implemented FEM scheme as well as with experiments measuring the sound pressure in a flow channel for various geometries and flow profiles. The results show good agreement between experiment and simulation. The limitations of this approach will be discussed.