Insights into the local heat transfer of a submerged impinging jet: Influence of local flow acceleration and vortex-wall interaction

The present study of low Reynolds number submerged impinging jets, re-examines the cause of peaks in the radial distribution of the Nusselt number by way of a direct numerical simulation. Two peaks, commonly named the inner and the outer, were particularly studied. The laminar flow behavior within a Reynolds number range of 392 ? Re ?  1804 as well as different velocity inlet profiles (parabolic, 7th power, uniform) were examined under axisymmetric conditions. The inner peak was found to be associated to the radial distribution of the radial flow acceleration, which is strongly influenced by the velocity profile of the incoming jet. Based on an energy balance, a critical inflow velocity near the wall for the presence of the inner peak was derived analytically. The uniform velocity profile generates strong radial acceleration, which leads to the required inflow and the occurrence of the inner peak. The outer peak was found to be related to the appearance of large scale vortices and their interaction with the heated wall. However, in order to generate such large scale vortices a fluctuating inlet velocity was required. Both peaks, existing under laminar flow conditions, were found not to be related to turbulence, as is widely assumed in literature.