HEAT TRANSFER PERFORMANCE OF A WAVY CHANNEL AND RELATED TURBULENCE STRUCTRE

Direct numerical simulation was performed for a low- Reynolds number turbulent flow of air over wavy surfaces and related heat transfer. Computationally targeted is an infinite channel having non-slip wavy and slip flat surfaces. The wave amplitude ratio, 2a/ α, is changed from 0 to 0.1 keeping the pressure drop constant. When the flat surface is deformed to sinusoidal shape, mean flow rate is seriously decreased with mild enhancement of heat transfer. Pumping power saving by the surface deformation was suggested so that the bulk Nusselt number for 2a/ α =0.1 was four times as large as that for flat plate consuming the same pumping power. Various kinds of turbulence statistics for flow and temperature fields for 2a/ α =0.1 are presented in order to clarify structures of scalar transport near the wavy surface. Local Nusselt number is high on the ascending part of wavy surface, and its peak locates between reattachment point and the wave crest. Two-dimensional display of statistics revealed that high value of heat transfer coefficient even for low flow rate occurs due to mean flow acceleration and activated turbulent transport normal to the wall near the reattachment point. Correlation between normal heat flux and normal component of velocity fluctuation suggested that enhanced redistribution of kinetic energy is essential to activation of turbulent transport.