Convective heat transfer from a spherical concave surface due to swirling impinging jets issuing from a circular pipe

Impinging jet heat transfer from curved surfaces is available in many industrial applications, such as cooling of gas turbine leading edge and deicing of airplane wing leading edge (heating). Most of the published studies on this topic involve non-swirling jet impingement from flat surfaces. Swirling jets are also used in some applications with the anticipation of heat transfer augmentation. Swirling impinging jet flow characteristics are significantly different from that of the non-swirling jet. However, fundamental studies of swirling jet impingement onto curved surfaces are very limited. As such, flow dynamics and convective heat transfer from a heated concave surface due to swirling impinging jets from a circular nozzle are numerically investigated using the RANS approach and the realizable k-epsilon turbulence model. Various flow and geometric parameters, such as the jet Reynolds number (Re) in the range of 11,600-35,000; the swirl number (Sw) in the range of 0-2.4; and the jet-tosurface separation distance (H) of 0.5-8 times the nozzle diameter, at a fixed impingement surface curvature (diameter) are studied. The results show that two counter-rotating recirculation zones appear near the target surface for near-field impingement (H <= 1) and higher swirl numbers (Sw >= 1.2), whereas for far-field impingements (H > 2), they are formed inside and outside of the main jet stream. An intense surface heat transfer zone develops only for near-field impingement in the range 1 <= S <= 3 at higher swirl numbers, where S is the distance along the impingement surface from the domain axis. More uniform thermal distribution along the curved surface is found for far-field impingement at Sw >= 0.8. Whilst the transitional Sw and H for Re = 11,600 are 0.8 and 2 respectively, the transitional Sw and H for Re = 35,000 are 0.8-1.2 and 4, respectively. Maximum heat transfer zones are found to be correlated with strong turbulence. Correlations are developed for the average Nusselt number as a function of the jet Reynolds number, jet exit to impingement surface separation distance, and swirling strength.