MEASUREMENTS IN BUOYANCY-ASSISTING LAMINAR BOUNDARY-LAYER FLOW OVER A VERTICAL BACKWARD-FACING STEP - UNIFORM WALL HEAT-FLUX CASE

Measurements and predictions of velocity and temperature distributions in buoyancy-assisting, laminar, mixed convection boundary layer flow over a vertical two-dimensional backward-facing step are presented. The wall downstream of the step was subjected to a uniform wall heat flux, and the wall upstream of the step and the step itself were kept adiabatic. Velocity and temperature distributions were measured simultaneously by using a laser-Doppler velocimeter (LDV) and a cold-wire anemometer. Flow visualization was also carried out to determine the reattachment length. The experiment covered a range of levels of wall heat flux (0 less-than-or-equal-to q(w) less-than-or-equal-to 290 W/m2), free-stream velocities (0.25 less-than-or-equal-to u(infinity) less-than-or-equal-to 0.7 m/s), and step heights (0.35 less-than-or-equal-to s less-than-or-equal-to 0.8 cm). The results indicate that as the wall heat flux increases, the Nusselt number increases but the reattachment length decreases. The measured results reveal that axial conduction along the constant heat flux surface is very significant in the recirculation region. This finding necessitates the coupling of the convective heat transfer from the wall to the fluid with the axial conduction along the constant heat flux wall in order to accurately predict the measured data by the numerical solution.