Flow structures and heat transfer characteristics in fan flows with and without delta-wing vortex generators

Abstract

Effects of an external delta-wing vortex generator on the flow and heat transfer characteristics in fan flows and uniform flows were experimentally investigated and compared. A heated plate, installed on the bottom wall of a duct, was used as the heat transfer surface. Three-component mean and fluctuating velocity measurements were conducted using a laser Doppler velocimetry to characterize the flow structures and to obtain the near-wall flow parameters, including the axial mean velocity, axial vorticity and turbulent kinetic energy. Temperatures on the heat transfer surface were measured using thermocouples to obtain the Nusselt numbers. Results show that the external delta-wing vortex generator in fan flows has little overall effect on the near-wall averaged axial mean velocity and axial vorticity, but increases the turbulent kinetic energy, in the investigated X/ D ranges. The increase in the turbulent kinetic energy by the delta-wing has little effect on heat transfer in the inherently vortical fan flows. Consequently, the delta-wing vortex generator in fan flows has little effect on the heat transfer augmentation.