Fluid flow and convective heat transfer of combined swirling and straight impinging jet arrays

Impinging swirling jets generate interesting flow fields. In this paper, the flow and heat transfer characteristics of a staggered combination of straight and swirling jets are reported in order to access flow details and to show complex flow structures as well as the strong coupling between the feeding and the exhaust phases experienced by the cooling air. Herein, numerical and experimental study are conducted for a given jet-to-jet distance s/D = 5 and nozzle-to-plate distance of HID = 4 to allow for the understanding of the thermo-fluid dynamic of multiple jets with swirl. The jets were arranged as a staggered array. The swirling jet assembly consists of a blade-type swirl generator. The different blade orientations give jets with different swirl intensities. Results obtained with swirling impinging jets are compared with those obtained with a circularimpinging jets in the same testing conditions. They supply information on the behavior of the resulting flow field. The flow patterns on an impinged surface are also visualized using oil film technique. Both the numerical and experimental analysis shows the cell topology and the resulting fountain flow at the impingement. It is found that every jet possesses an independent cooling area on the impingement plate. The dependence of heat transfer rate and uniformity on the swirl is also explained. In particular, this study shows that the swirl motion can affect mixing at a short distance from the nozzles exit but it rapidly loses its intensity which limits the contribution to wall interference. (C) 2014 Elsevier Ltd. All rights reserved.