Wake of a self-propelled body, part 1: Momentumless wake

Experiments were performed in the turbulent boundary layer and near wake of an axisymmetric body propelled by a jet to study the evolution of the momentumless wake. Comparisons with measurements in the drag wake of the body (without the jet) and in the isolated jet provide an understanding of initial mixing between the two flows. Triple-sensor hot wires and multitube pressure probes were used to measure the mean velocity, turbulence, and pressure fields from the jet exit to a distance of over 15 jet diameters. It is found that the evolution of the wake takes place in three distinct stages: a zone close to the jet exit, about 4 jet diameters long, where the jet shear layer mixes with fluid from the wall region of the boundary layer; an intermediate region, about 12 jet diameters long, where there is mixing between the boundary layer and the jet up to the axis; and the third region where the two fleas lose their identities to become a single shear layer and the mean how acquires some of the characteristics of self-similar hows. However, the momentumless wake does not conform to the assumptions and results of classical similarity analysis.