Numerical simulation of local disturbances in absolutely/ convectively unstable flow by a vortex method

Abstract

The development of a local disturbance in a two-dimensional incompressible wake is simulated numerically using a vortex dynamics method. The evolution of a wave packet in an absolutely and in a convectively unstable wake flow is compared. The main attraction of the used vortex method lies in its Lagrangian nature, which in inviscid flows preserves the identity of rotational fluid elements and thereby allows for the tracking of individual vortex lines or tubes. Due to the non-linearity of the employed method, the analysis is not restricted to small amplitudes. It is easily applicable to unsteady flows and the basic state does not have to be locally parallel.