Computation of aeroacoustic phenomena in subsonic and transonic ducted flows

A sonic flow in a plane duct passing an abrupt increase in cross-section is numerically studied by solving the 3-D compressible Navier-Stokes equations. Different flow patterns are likely to appear in such configuration. For a very low downstream pressure, the flow is entirely supersonic. For higher pressures, unstable flow patterns emerge. One of these patterns features a normal shock, that oscillates due to a self-exciting mechanism. As the duct is open at the outflow, aeroacoustic coupling occurs when the shock oscillations get in resonance with the longitudinal acoustic modes of the duct. The main flow features are well captured by the present numerical simulations but no coupling with longitudinal duct modes is found. The governing equations are solved using high-order methods based on central finite differences. To damp out spurious oscillations supported by central differences selective filtering and a well established non-linear shock-capturing term are used. A high-order overset grid approach is implemented in order to tackle with complex geometries.