TURBULENT NATURAL CONVECTION FLOW OVER A BACKWARD-FACING STEP

Measurements of turbulent natural convection boundary-layer air flow over a two-dimensional, vertical, backward-facing step are reported. The step geometry consists of an adiabatic backward-facing step, an upstream wall, and a downstream wall. Both the upstream and downstream walk are heated to a uniform and constant temperature. Laser-Doppier velocimeter and cold-wire anemometer were used, respectively, to measure simultaneously the time-mean velocity and temperature distributions and their turbulent fluctuations. The experiment was carried out for step heights of 0, 11, and 22 mm and a temperature difference, (delta)T, of 30°C between the heated walls and the ambient air. The present results reveal that the turbulence intensity of both the streamwise and transverse velocity fluctuations, and the intensity of temperature fluctuations downstream of the step, increase as the step height increases. Also, it was found that both the reattachment length and the heat transfer rate from the downstream heated wall increase with increasing step height.