Effects of multiple trapezoidal vortex generators on flow and surface cooling

Flow and heat transfer experiments have been conducted to study the effects of multiple trapezoidal vortex generators on flow structure and surface cooling. The resulting vortical structures and their surface cooling effects in the wake region of the VGs were studied using planar particle image velocimetry (PIV) and infrared (IR) thermography. PIV was used to determine the mean flow distribution and shear rate of flowing air near the wall, while IR thermography was used to measure surface temperature. Experiments were performed at a fixed Reynolds number of 4800 based on the hydraulic diameter of the duct. The width-to-spacing ratio (WTS) of the VGs have been varied to understand the role of the down-flow motion of the counter-rotating vortex pairs (CVPs) on local heat transfer enhancement. Experimental results reveal that a significant cooling effect is obtained when the induced flow by the CVP is accelerated in the streamwise direction within the boundary layer while the vortices are kept adjacent to the surface. Results to date also show that heat transfer enhancement can be correlated to the local shear rate measured near the wall (y⁺ < 5).