Turbulent flow structure and heat transfer mechanisms over surface vortex structures of micro V-shaped ribs and dimples

Abstract

Turbulent flow and heat transfer characteristics in the channels with surface vortex structures of micro V-shaped ribs, dimples, and their hybrid structures have been investigated by carrying out delayed detached eddy simulations (DDES) at the Reynolds number of 50,500. It is found that, for the micro V-shaped rib, lower turbulent mixing is produced behind the leeward rib region, while the stronger longitudinal vortex pairs induced by the V-shaped ribs enhance the convective transport of heat. For the dimple, the shed vortices and the shear-layer vortices increase the near-wall turbulent mixing. The complex secondary flows induced by the flow separation, attachment and ejection increase the convective transport of heat. However, the flow separation produces a dead-air zone limiting the further increase of heat transfer enhancement. For the micro V-shaped rib-dimple hybrid structure, the strong downwash flow induced by the micro V rib breaks the recirculation zone inside the downstream dimple and the dimple here works as a vortex amplifier, which produces much stronger longitudinal vortex pairs. This process enhances both the turbulent mixing and convective transport of heat. Therefore, the micro V-shaped rib-dimple hybrid structure provides even more pronounced heat transfer enhancement.