Spatio-Temporal Characteristics of Turbulent Heat Transfer for a Backward-Facing Step Flow(Thermal Engineering)

Abstract

Spatio-temporal distribution of convective heat transfer behind a backward-facing step was measured in order to explore the mechanisms of the heat transfer caused by flow separation and reattachment. This measurement was achieved using a high-speed infrared thermograph that recorded temperature fluctuations on a thin foil heated electrically. The attenuation resulting from both the thermal inertia and lateral conduction of the test surface was restored by solving heat conduction equations inside the surface. As a result, it was clarified that the heat transfer enhancement in the flow reattaching region had a spot-like characteristics. Each spot spread with time and overlapped with others to form a complex feature in terms of spatio-temporal characteristics of the heat transfer. The typical spanwise wavelength of this structure was approximately 1.2 times the step height for Reynolds number of 2000≤Re_H≤5500, regardless of the step height. The typical frequency of the fluctuation in the reattaching region was St=0.04-0.08, although there was no clear periodicity. This fluctuation is likely to be related to the low-frequency unsteadiness reported in previously published literature.