Experimental investigation of turbulent separated-reattachment flow by using LDV

A turbulent separation-reattachment flow in a two-dimensional asymmetrical curved-wall diffuser was surveyed with a two-dimensional laser doppler velocimeter. The turbulent boundary layer was separated on the lower curved wall under strong pressure gradient and then reattached subsequently on a parallel channel. At the inlet of the diffuser, the Reynolds number based on the diffuser height is 1.2 x 10(exp 5) and the velocity is 25.2 m/s. The results of the experiments in newly defined streamline-aligned coordinates are presented and analyzed. The experiment showed that after Transitory Detachment there was a second extremum of normal Reynolds stress and shear stress appeared as a minus in the near-wall backflow region. A scale was formed using the maximum Reynolds shear stress. It was found that Reynolds shear stress similarity exists from separation to reattachment and the Schofield-Perry velocity law exists in the forward shear flow. Both profiles were used in the experimental work that led to the design of a new eddy-viscosity model. The length scale came from that developed by Schofield and Perry. the composite velocity scale was formed by the maximum Reynolds shear stress and Schofield-Perry velocity scale as well as the edge velocity of the boundary layer. The results of these experiments are presented in this paper.