NUMERICAL PREDICTIONS OF FLOW STRUCTURE AND LOCAL NUSSELT NUMBER RATIOS ALONG AND ABOVE DIMPLED SURFACES WITH DIFFERENT DIMPLE DEPTHS IN A CHANNEL

Abstract

Turbulent air flows in channels with dimples placed on the bottom wall are numerically predicted and compared using version 6.0.12 of FLUENT with a realizable k-ε model and no wall function. Three different dimple depths, δ/D = 0.1, 0.2, and 0.3, are considered. Steady-state predictions of fluid within and near different dimples show the presence of different vortex pairs. These include centrally located vortex pairs as well as vortex pairs located near the spanwise edges of individual dimples, which become stronger as dimple depth increases. Magnitudes of eddy diffusivity for momentum and eddy diffusivity for heat are augmented at the same locations, and also increase as dimple depth increases. Such characteristics are due to advection of reattaching and recirculating flow from locations within the dimple cavities, as well as to the strong instantaneous secondary flows and mixing within the vortex pairs. Local Nusselt number ratio data also show the highest augmentations, and the highest local values that increase with dimple depth at surface locations beneath the different vortex pairs, especially within the downstream portions of dimples, as well as near dimple spanwise and downstream edges.

The work reported in this article was sponsored by the National Science Foundation, grant NSF-GOALI CTS-0086011. Dr. Stefan Thynell and Dr. Richard Smith were the NSF Program monitors.