Measurements of laminar mixed convection in boundary-layer flow over horizontal and inclined backward-facing steps

Abstract

Measurements and predictions of velocity and temperature distributions are presented for buoyancy-assisting mixed convection laminar boundary-layer flow over horizontal and inclined, twodimensional backward-facing steps. Laser-Doppler velocimeter and cold wire anemometer are used to measure simultaneously the velocity and the temperature distributions, respectively. Flow visualizations are carried out to determine the reattachment length and the onset/start of vortex instability for different wall temperatures (0°C ⩽ Δ T⩽ 30°C), free stream velocities (0.285 m s −1 ⩽ u ∞ ⩽ 0.7 m s −1), step heights (0.35 cm ⩽ s ⩽ 0.8 cm), and inclination angles (30° ⩽ φ ⩽ 90°) as measured from the vertical direction. For the horizontal case, the buoyancy force has a negligible effect on the velocity and temperature distributions, but it influences significantly the onset/start of instability. The inclination angle, on the other hand, affects significantly the temperature and velocity distributions. As the inclination angle from the vertical increases, the local Nusselt number decreases, while the reattachment length and the location of the maximum Nusselt number behind the backward-facing step increase.