Modelling the effect of roughness density on turbulent forced convection

Abstract

By examining a systematic set of direct numerical simulations, we develop a model which captures the effect of roughness density on global and local heat transfer in forced convection. The surfaces considered are zero-skewed three-dimensional sinusoidal rough walls with solidities, Λ (defined as the frontal area divided by the total plan area), ranging from low Λ=0.09, medium Λ=0.18 to high Λ=0.36. For each solidity, we vary the roughness height characterised by the roughness Reynolds number, k+, from transitionally rough to fully rough conditions. The findings indicate that, as the fully rough regime is approached, there is a pronounced breakdown in the analogy between heat and momentum tra..