LES studies o the interaction of a free shear layers with a proximate wall in post-reattachment recovery and a plane turbulent wall jets

Many wall-bounded turbulent flows are characterized by a complex interaction between the outer shear layer, the structure of which is similar to a free shear layer, and an inner layer, which is essentially a perturbed boundary layer. Examples in which such an interaction occurs are separated flows recovering from reattachment, wall jets used in the context of wall cooling, heating and separation control, and impinging jets used to enhance heat transfer. Two different flow configurations presenting related interactions are considered in the work summarised herein, Fig. 1. One is a wall jet and the other a backward-facing-step flow. In the latter, interest is focused especially on the interaction in the post-reattachment-recovery region and the near-wall region within the lower portion of the recirculation zone. In both these areas, an „outer‟ shear layer interacts with the boundary layer, and is of interest to explore whether these have features akin to those in a wall jet. A specific objective is to gain insight into why most RANS closures do not represent post-reattachment recovery well. To this end, second-moment budgets have been examined, and used in a-priori studies of closures, the latter reported in Dejoan et al. (2006). Preceding the work summarised herein, the flow and turbulence physics of wall jets, with a real frictional wall as well as frictionless wall, were studied in detail by means of highly resolved LES (Dejoan and Leschziner (2007), (2007 1 )). The emphasis of these studies was to identify the processes by which the near-wall layer interacts with the separated (free-shear) layer above it, and on separating frictional from inertial effects on turbulence features at the wall. The present study targettedv the identification of generically common features between the wall jet and interacting shear layers in separated flow.