Corrugated walls are widely used as passive devices for heat and mass transfer enhancement; they are most effective when operated at transitional and turbulent Reynolds numbers. In the present study, direct numerical simulation is used to investigate the unsteady
forced convection in sinusoidal, symmetric wavy channels. A novel numerical method is
employed for the simulations; it is meant for fully developed flows in periodic ducts of
prescribed wall temperature. The algorithm is free of iterative procedures; it accounts for
the effects of streamwise diffusion and can be used for unsteady problems. Results of two
simulations in the transitional regime for Reynolds numbers based on average duct
height and average velocity of Re= 481 and Re= 872 are reported. Time averaged and
instantaneous velocity and temperature fields together with second-order statistics are
interpreted in order to describe the mechanism associated with heat transfer augmentation. Heat flux distributions locate the most active areas in heat transfer and reveal the
effects of convective mixing. Slanted traveling waves of high temperature are identified;
peak values of Nusselt number are attained when the high-temperature fluid of the waves
reaches the converging walls.
