FLOW STRUCTURE AND HEAT-TRANSFER IN A CHANNEL WITH MULTIPLE LONGITUDINAL VORTEX GENERATORS

Experimental results of flow structure and heat transfer enhancement by longitudinal vortices in plane channels built by parallel plates in the transition flow regime are presented. The longitudinal vortices are generated by single and double rows of delta half-wing vortex generators punched out of the channel wall. The investigations are performed by a laser light sheet technique for flow visualization and unsteady liquid-crystal thermography for local heat transfer measurements. For an aligned arrangement of two rows of vortex generators, the experiments show that the flow structure in the wake of the second row is qualitatively similar to that of the first row. The peak value of the span-averaged Nusselt number at the wake of the second row is strongly dependent on the spacing of the two rows. For streamwise distances between the two rows of about seven channel heights this peak value is larger than the peak value of the span-averaged Nusselt number at the wake of the first row.