Flow structure and local Nusselt number variations in a channel with dimples and protrusions on opposite walls

Flow structure characteristics are presented for a channel with a dimpled surface on one wall, both with and without protrusions (with the same shapes as the dimples) on the opposite wall. Channel aspect ratio is 16, ratio of channel height to dimple print diameter is 0.5, and Reynolds numbers based on channel height range from 380 to 30,000. Instantaneous flow visualization images and surveys of time-averaged flow structure show that the protrusions result in added vortical, secondary flow structures and flow mixing. As a result, local friction factors and local Nusselt numbers are augmented compared to a channel with no protrusions on the top wall. For Nusselt numbers, such augmentations are present near the downstream edges of dimple rims mostly near dimple diagonals, as well as on flat surfaces immediately downstream of dimple rims.