Modelling the acoustic scattering and absorption at an area expansion in a flow duct requires the incorporation of the flow-acoustic interaction. The vortex sheet model is an analytical linear acoustic model, where the flow field at an area expansion in a duct is described as a jet issuing into the larger part of the duct. In this paper, we study plane wave propagation at such an area expansion. The flow-acoustic interaction is described in terms of energy flow. A classification of modes as "hydrodynamic" and "acoustic" is used to separate the acoustic energy from the part of the energy arising from the steady flow field. Theoretical results are presented together with experimental data. The energy distribution and dissipation of acoustic energy is studied schematically, indicating the effects of the flow acoustic interaction due to the area expansion and the sharp edge.
QC 20140819