Wake instabilities behind an axisymmetric bluff body at low Reynolds numbers

Abstract

This paper aims at understanding the dynamical process that leads to the onset of chaos in the flow past a blunt based axisymmetric bluff body. On the ba- sis of direct numerical simulations, conducted for Reynolds numbers ranging from 100 to 800, we show that the flow undergoes multiple transitions, successively giv- ing rise to the SS, RSPa, RSPb and RSPc wake states. In particular, the RSPc state, revealed in this work via long-term computations, is characterized by intermittent vortex stretching denoting the onset of chaos and the potential occurence of a third instability that superimposes to the first and second instability associated with state RSPa and RSPb respectively. Interestingly, the reflectional symmetry plane that characterizes the RSP states is still retained. Hence, chaos is triggered before the symmetry breaking and the occurence of the RSB state observed at higher Reynolds numbers.