Investigation on momentum and heat transfer in a reattaching separated shear layer

Abstract

Momentum and heat transfer characteristics have been studied in a separated, reattached and then redeveloping turbulent shear layer past a two-dimensional normal fence. Mean velocity vector and static pressure field have been measured in the whole flow field by using a 3-hole pitot tube and a hot-wire anemometer. Flow visualization, wall pressure distribution measurements have also been carried out. Streamline curvature field behind the fence has been obtained by using the data of total velocity vector field. It was found that upstream of the reattachment point behind the fence, the separated shear layer develops as a stabilizing curved mixing layer. It was also found that the mean velocity field does not follow the equilibrium boundary layer profile in the redeveloping region where the streamline curvature already vanishes at X/Xr=2.4 where Xr is the reattachment length. Extensive single point measurements of second-and third-order moments of velocity fluctuations have been made in a separated, reattached and then redeveloping turbulent shear layer past a two-dimensional normal fence. Near the reattachment zone, the Reynolds stresses and the triple products were found to decrease due to large eddy distortions by the effects of strong pressure fluctuations and by the presence of the solid wall boundary. Budgets in the balance equations for the turbulent kinetic energy and the Reynolds shear stress have been obtained, and they were compared with those of the free shear layer and of the boundary layer. The budget profiles change rapidly as the reattachment process progresses. The budget profiles were observed to be different from those of the equilibrium boundary layer even far downstream in the redeveloping boundary layer. It has been shown that the streamline curvature influences the turbulence structure in the separated free shear layer and that the pressure diffusion has significant contributions to the budget balances of the turbulent kinetic energy equat...