Effect of Time-Varying Wake Flow Characteristics Behind Flat Plates

Experimental analysis is presented of high-speed white light differential interferometry and shadow visualizations recorded at the trailing edge of flat plates that have been designed to represent the unsteady near-wake flow characteristics behind turbine blades. The effects of the boundary-layer state and thickness on the characteristics of the time-varying wake flow have been analyzed by synchronizing visualizations with unsteady pressure measurements at the trailing edge. It is shown that, when the boundary layer is turbulent, the vortex shedding frequency depends on the boundary-layer thickness, but the unsteady pressure intensity measured at the trailing edge does not. The recirculation domain is longer when the boundary layer is quasilaminar, which explains why the disturbances from the vortex street are much less perceived at the trailing edge. Finally, the analysis of interferograms and unsteady pressure indicates a strong coupling between the vortex street and the flow over the model