Numerical investigation of the heat transfer performance of pulsating jet impingement onto a dimpled/protruded surface

The SST turbulent model coupled with γ- Re θ was adopted in the present numerical research of the cooling performance of pulsating jet impingement onto dimpled/protruded surfaces. The turbulent model has been experimentally validated and it proves that the coupled turbulent model can well predict jet impingement. User Defined Function was used in the investigation. Grid independence validation has been performed and a set of structured grids was employed with y +<1. The results show the area-averaged Nu varies with the same pulsating frequency in different target morphology cases. The pulsating amplitude for the f = 80 Hz cases shows the largest value among all the cases. Both the area-averaged Nu and the area-averaged time-averaged Nu increase with the increasing pulsating velocity ratio and decrease with the increasing pulsating frequency. The heat transfer performance is clearly enhanced in the stagnation and secondary impingement regions in the protruded cases. Thus, the time-averaged Nu in all the protruded cases is higher than that in the flat cases. The secondary impingement also leads to a higher local Nu outside of the dimple edge compared with the flat case. The local stagnation Nu varies with the same frequency as the pulsating jet impingement. The pulsating amplitude of the local stagnation Nu shows the largest value in the protruded surface case. The largest value shows the smallest time in one cycle for the protruded surface cases. The local stagnation time-averaged Nu increases with the pulsating velocity ratio and frequency in both dimpled and flat cases, while it remains almost unchanged in the protruded case. The rate of increase in the dimpled cases is higher than that in the flat case. The case with lower pulsating frequency and higher pulsating velocity in the protruded target surface shows better heat transfer enhancement performance in the comparison.