Direct Numerical Simulation of Turbulent Flow and Heat transfer over Riblets

Riblets are well known as a passive mean for drag reduction in turbulent flow conditions, but their effectiveness for heat transfer is quite controversial, since the available experimental and theoretical investigations did not clearly establish whether riblets, with different cross sections, produce a net variation in heat transfer in comparison to the flat plate value. In this paper, we report our preliminary numerical results for fully developed laminar and turbulent flow and heat transfer in a channel with triangular riblets. The study is performed by means of direct numerical simulation at a Reynolds number, based on the wall-shear velocity, Re = 10 and Re = 180 for the laminar and turbulent case, respectively, for a fluid with a Prandtl number Pr = 0.71. Two different ribbed channels are considered, under a constant heat flux boundary condition. The results obtained are in general agreement, for the flow and turbulent quantities, with past experimental and numerical studies, but the predicted heat transfer efficiency, in the turbulent regime, is significantly lower than some of the experimental studies.