TWO-PORT CHARACTERIZATION OF FLOW-ACOUSTIC EFFECTS IN A RECTANGULAR MUFFLER GEOMETRY

One dimensional linear acoustic network models are commonly used for the acoustic development of exhaust systems. These models are advantageous since they allow the characterization of the scattering matrices for individual elements, independent of the upstream or downstream components. For an exhaust assembly, the individual elements can be combined by a simple multiplication of the individual matrices to assess the propagation characteristics of the whole system under consideration. Accurate numerical methodologies are required to predict the aeroacoustic transmission characteristics of these components, in the presence of a non-uniform mean flow. In this paper, a numerical approach using Linearized Euler Equations (LEE) is adopted to predict the aeroacoustic propagation for a simple rectangular expansion chamber. The mean flow field is obtained using a Reynold's Averaged Navier-Stokes (RANS) simulation. Since the standard LEE are prone to unphysical instabilities, different modeling approaches are suggested to overcome the instabilities and their effect on the two-port characteristics prediction is evaluated.