Heat transfer and fluid mechanics measurements in the turbulent reattaching flow behind a backward-facing step

Stanton number profiles show a peak in the heat transfer rate about 2/3 of a step height upstream of reattachment. The heat transfer rate does not behave like the mean skin friction, but shows a strong correlation with the level of the fluctuating skin friction. Power law correlations of the maximum Stanton number show dependence on the step height Reynolds number to the -0.4 power and the bounday layer thickness at separation to the -0.1. For a constant wall heat flux, the redeveloping thermal boundary layer has its effective origin two step heights downstream of reattachment. Downstream of reattachment the thermal boundary layer resembles an unheated starting length flat-plate boundary layer. The near-wall region controls the heat transfer rate throughout the flow. The heat transfer rate is seen to be a function of the thickness of the laminar layer, which thins in the reattachement region to less than 1/4 that under the redeveloping boundary layer. The flow near the wall under the recirculation bubble is a laminar-like flow with high levels of unsteadiness.