Turbulence characteristics of radially-confined impinging jet flows

Abstract

Radially confined, axisymmetric impinging jet flows are investigated by using the standard particle image velocimetry experimental technique. The confinement is achieved by placing a confinement block around a jet, co-axially. The inner diameter of the block is successively varied to nine different values. The inlet-based Reynolds number of the jet is kept constant at 5000. The nine diametric values yielded nine different flows of widely different characteristics. Among other usage, an insight into the flow characteristics can be helpful in designing compact impinging jet applications, as such a radially confined flow is equivalent to passing the pre-impingement jet through a hole perforated in a solid wall (i.e. the jet source can be placed behind a wall). The study has revealed that the flows, in general, form two circulation zones, three mixing layers, and two boundary layers. Based on turbulence characteristics of the five shear layers, overall characteristics of the flows are understood systematically. Mean velocity and various turbulence statistics are also presented, and mechanisms underlying behind their variations are explained. Finally, scaling laws are obtained for the mean velocity and for the turbulence statistics, both in the impingement and in the wall jet regions.