Characteristic behaviour of turbulence and transport phenomena at the stagnation region of an axi-symmetrical impinging jet

This paper presents the experimental results of the flow field and heat transfer characteristics in the stagnation region of a round, submerged, impinging jet. From the detailed observations of stagnation flow field with the aid of flow-visualization techniques, the structures of axi-symmetrical impinging jet have been clasified depending on H/D. When the impingement plate is placed in the transition region, the turbulence becomes most vigorous and there exist the coherent structures in large scales which have remarkable streamwise vorticities. These structures have been extensively investigated both qualitatively and quantitatively and their close relation is further confirmed with the natural distortion and coalescence of ring vortex filaments in the upstream shear layer. The effects of these large-scale eddy structures on the enhancement of heat transfer rate are also investigated successively and it is concluded that they are predominant in the passive quantity transports in the stagnation flow region. Finally, the vorticity amplification and heat transfer augmentation mechanisms are discussed in comparison with those of plane impinging jets.