Heat transfer enhancement by delta-wing-generated tip vortices in flat-plate and developing channel flows

Using delta wings placed at the leading edge of a flat plate, streamwise vortices are generated that modify the flow; the same wings are also used to modify a developing channel flow. Local and average measurements of convection coefficients are obtained using naphthalene sublimation, and the structure of the vortices is studied using flow visualization and vortex strength measurements. The pressure drop penalty associated with the heat transfer enhancement of the channel flow is also investigated. In regions where a vortex induces a surface-normal inflow, the local heat transfer coefficients are found to increase by as much as 300 percent over the baseline flow, depending on vortex strength and location relative to the boundary layer. Vortex strength increases with Reynolds number, wing aspect ratio, and wing attack angle, and the vortex strength decays as the vortex is carried downstream. Considering the complete channel surface, the largest spatially averaged heat average heat transfer enhancement is 55 percent; it is accompanied by a 100 percent increase in the pressure drop relative to the same channel flow with no delta-wing vortex generator.