Numerical Analysis of Flow Structure Above Dimpled Surfaces with Different Depths in a Channel

Turbulent air flow characteristics in channels of three different dimple depth (delta/D=0.1, 0.2, and 0.3) placed on the bottom wall are numerically predicted using FLUENT for Reynolds number based on the channel height, Re (H)=20,000, and the ratio of channel height to dimple print diameter, H/D=1.0. The turbulence model employed is a realizable k-epsilon model with no wall function. Steady-state analyses of fluid within and near different dimple depths demonstrate the existence of different vortex pairs. These vortex pairs are investigated at the central position of dimples as well as near the spanwise edge of individual dimples, and become stronger as dimple depth increases. In addition, steady-state results show that the streamwise vorticity distributions, which are associated with the flow recirculation zones positioned within the upstream halves of each dimple, are higher in magnitude and cover larger spatial extents as the dimple depth increases. Magnitudes of eddy diffusivity for momentum and eddy diffusivity for heat are also augmented by the vorticity concentrations within and downstream of individual dimples as the dimple depth increases. Such characteristics are due to the advection of reattaching and recirculating flow within the dimple cavities, as well as to the strong instantaneous secondary flows and mixing within the vortex pairs.