Combined flow and heat transfer measurements of backward facing step flows under periodic perturbation

Abstract

The flow fields and convective heat transfer downstream of a backward facing step (BFS) with a ReH=9630 were investigated using experimental methods. The BFS flow was perturbed using a synthetic jet actuator deployed at the separation point with a range of perturbation frequencies (fAH/Uo=0.04-0.39) and amplitudes (uA′/Uo=0.3-0.9). The momentum transport across the shear layer appeared to be enhanced by the perturbations, resulting in a shortened recirculation bubble, a larger curvature in the time-average streamline over the separation bubble and enhanced heat transfer rate in the attachment and recirculation regions. The distributions of the reattachment length, streamline curvature, static base pressure, turbulent kinetic energy and convective heat transfer rate all suggested there was a critical perturbation frequency fAH/Uo≈0.22 where the perturbation frequency matched the characteristic frequency of the attaching shear layer. Flow changed only slightly with the perturbation amplitude when fAH/Uo≳0.22 but changed significantly when fAH/Uo≲0.22.