Turbulent mixed convection flow over a forward-facing step-the effect of step heights

Measurements of heat transfer and fluid flow of turbulent mixed convection boundary-layer air flow over an isothermal two-dimensional, vertical forward-facing step are reported. The upstream and downstream walls and the step itself were heated to a uniform and constant temperature. Air velocity and temperature distributions and their turbulent fluctuations are measured simultaneously by using, respectively, a two-component laser-Doppler velocimeter (LDV) and a cold wire anemometer. The present study examines the effect of forward-facing step heights on turbulent mixed convection flow along a vertical flat plate. The experiment was carried out for step heights of 0, 11, and 22 mm, at a free stream air velocity, u∞, of 0.55 m⋅s−1, and a temperature difference, ΔT, of 30 °C between the heated walls and the free stream air (corresponding to a local Grashof number Grxi=6.45×1010). It was found that the turbulence intensity of 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.