Heat Transfer Enhancement by Delta-Wing Vortex Generators on a Flat Plate: Vortex Interactions with the Boundary Layer

New data are presented that demonstrate a 50% to 60% enhancement of average heat and mass transfer for flow over a flat plate at low Reynolds numbers, using delta-wing vortex generators. The mechanisms responsible for the enhancement are determined, and a single parameter for estimating their effect is established. Using a straightforward method for evaluating this parameter from flow visualization data, optimal delta-wing geometries were found for Reynolds numbers of 600, 800, and 1000 based on wing-chord length. The results were also used to develop a clearer understanding of the interactions between the vortex and boundary layer. When a high-circulation vortex is placed near the edge of the boundary layer, it effectively thins the boundary layer; the vortex advects free-stream fluid into the temperature or species boundary layer. Vortices should be generated in a common inflow arrangement so that induced velocities keep the vortices near the boundary layer.