The heat transfer mechanism of a swirling impinging jet in the stagnation region

Heat transfer mechanism of a swirling impinging jet in the stagnation region has been experimentally examined, using a combined technique of particle image velocimetry (PIV) and laser induced fluorescence (LIF) for the simultaneous measurements of velocity and temperature fields. The present study indicated that the radial width of the jet was stretched with increasing swirl number Sw, and that this stretching phenomena contributes to radially the maximum local heat transfer coefficient. At the stagnation region, the flow near the heated surface was mixed intermittently by reverse flows toward upstream, and spatial distributions of temperature were well correlated with instantaneous velocity vector maps. The dynamic behavior of recirculation zones, which were attributed to swirl number Sw and impinging distance, mainly determined the turbulent heat transfer at the stagnation region.