DNS of Heat Transfer in a Transitional Channel Flow Accompanied by a Turbulent Puff-like Structure

Abstract — Direct numerical simulation of heat transfer in a fully developed channel flow has been carried out in a range of low Reynolds numbers from Reτ = 180 to 60 with emphasis on the puff-like structure. For Reτ ≤ 80 with the largest box of 51.2δ × 2δ × 22.5δ, the turbulent puff in a channel is observed and significantly affects the momentum and heat transports. The spatial structure of the equilibrium puff is examined with taking account of two different thermal boundary conditions. It is revealed that there exists a localized strong turbulent region, in which the secondary flow is induced by the puff. In consequence, at the present lowest Reynolds number as low as Reτ = 60, the flow remains turbulent and the larger Nusselt numbers than those without puff is obtained. 1