Flow and Heat Transfer Characteristics of Single Jet Impinging on Dimpled Surface

Based on combined particle image velocimetry (PIV) and numerical simulation, the flow and heat transfer characteristics of a single jet impinging on a dimpled surface for D_j/D = 0.318, 0.5, 1.045; δ/D = 0.1, 0.2, 0.3; Re_j = 5000, 10,000, 23,000, were investigated for the first time. The distance between jet nozzle and plate was fixed and equal to H/D = 2. The results show that the flow structures of the single jet impingement with dimpled target surface can be summarized into three typical conceptual flow structures. Particularly, the third flow structure in the form of a large toroidal vortex bound up with the dimple is the result of the centrifugal force of the flow deflection at the stagnation region and spherical centrifugal force of the deep dimple surface. The heat transfer area increases when the dimple relative depth increases. For the cases of D_j/D = 0.318 and 0.5, the area increasing dominate the heat transfer process, and the average Nusselt number increases with the increasing of dimple relative depth. For the cases with D_j/D = 1.045, the local Nusselt number reduction dominate the heat transfer process, the average Nusselt number decreases with the increasing of dimple relative depth. The average Nusselt number of the D_j/D = 0.318 and 0.5 cases is larger than the baseline case, while those of the D_j/D = 1.045 cases are smaller than the baseline case. Furthermore, the correlative expressions of the local Nusselt number, stagnation points Nusselt number and average Nusselt number are obtained.