Axisymmetric jet impingement on a dimpled surface: Effect of impingement location on flow field characteristics

Few studies have investigated the flow characteristics of jets impinging on dimpled surfaces that may increase or decrease their heat transfer capabilities. Here, particle image velocimetry (PIV) measurements have been performed on a round jet (diameter D) impinging on a surface having large spherical dimples (opening size d), D/d = 0.83. In particular, the effect of jet impingement location on the flow field was investigated. Impingement of the jet centered on the dimple as well as on the flat surface between the dimples (isthmus), was compared to impingement on a smooth surface. Measurements were performed at three Reynolds numbers, = 1,352, 6,268 and 12,342 at a stand-off distance of 4.8D. Results showed that the flow field in the developing wall jet strongly changed for isthmus impingement while for dimple and smooth impingement it was similar. However, outer-layer self-similarity was not attained in the developing wall jet. Furthermore, secondary vortex generation as a result of primary vortex impingement, was the same for smooth and dimple impingement while for isthmus impingement, secondary vortices were created through the generation of an unsteady separation bubble.