A theoretical study of the frequency selection mechanisms in afterbody unsteadiness
Abstract
The hydrodynamic stability theory is used to investigate the frequency selection in the flow behind an axisymmetric blunt based body. We present two theoretical approaches, resulting in different frequencies that are compared to the natural frequency observed in experimental configurations: we use the framework of local stability, in which vortex shedding arises from the transition to absolute instability of a large scale oscillating mode of azimuthal wave number m=1, and that of global stability accounting for the non-parallelism of the flow in the recirculating area. The differences between both approaches are discussed and an interpretation is proposed, based on the non-linear saturation effects.