Wake-induced shear layer excitation in a basic annular jet.

Abstract

The excitation of an outer shear layer by disturbances associated with wake structures shedding from the central body in an annular basic jet is studied here by means of the conditional sampling technique. The educed velocity perturbations show that at locations upstream of the rollup of the first thin initial vortices, the outer shear layer is already under a slight oscillation at the wake shedding frequency. This instability which triggers the formation of the wake induced structures in the outer shear layer and the geometrical structure of these structures seem to be governed largely by the large scale lateral velocity fluctuations of the quasi two dimensional orderly pattern of the shedding wake structures in the inner region. (A)