Study of Unsteady Thermal and Flow Structure near Reattachment Point behind a Backward Facing Step with POD Analysis

Abstract

In this study, the mechanism of heat transfer enhancement near the reattachment point behind a backward facing step is experimentally investigated at a Reynolds number of 5400. The unsteady fluctuations of the velocity and temperature were simultaneously measured by using 2 dimensions and 3 components (2D-3C) Particle Image Velocimetry (PIV) at x/H = 4.5 and the high-speed infrared (IR) thermograph on the heated wall. In order to discuss the thermal and flow structure near the reattachment point, 3 components of the velocity and the heat transfer coefficient were calculated. The spatial distribution of the flow and thermal fluctuations was reconstructed by using proper orthogonal decomposition (POD) analysis. As a result, the characteristic structure of the flow and thermal fluctuations appeared for the lower number of POD modes. These downwash and upwash flow in the transverse direction corresponded to the increasing and decreasing of the heat transfer coefficients at x/H of 4.5.