Flow field and thermal behaviour in swirling and non-swirling turbulent impinging jets

Results show the effects of swirl on impingement heat transfer depend on impingement distance. In the near-field (H = 2D), high jet turbulence (u'u' and w'w') close to the surface (0.8 mm upstream) correlate very well with Nusselt number peaks resolved on the heated surface. The occurrence of any pockets of low turbulent kinetic energy (k) near the surface may cause localised Nu trough, which can also be correlated with the presence of swirl induced recirculation zones if they stabilise on the surface. Alternatively, in the case of far-field impingement (H = 6D), swirl causes wider jet spread and hence turbulence levels are reduced. At this distance, non-swirling jets thus yield higher Nu zones at the surface.