Effects of vortex generators on the jet impingement heat transfer at different cross-flow Reynolds numbers

Experiments are carried out to investigate the effects of vortex generators on the jet impingement heat transfer in cross-flow. This study is a continuation of our previous research (Wang et al., 2015). In the present paper, the jet Reynolds number is fixed at 15,000 and the cross-flow Reynolds number varies from 40,000 to 64,000. The nozzle-to-surface distance to jet diameter ratio is 4.0. A vortex generator pair (VGP), placed in the cross-flow channel and upstream of the jet exit, is to enhance the impingement heat transfer. Both delta winglet (DW) and rectangular winglet (RW) are applied with different heights. Measurements of detailed heat transfer distributions on the impingement wall are conducted. Results show that the presence of VGP substantially augments the impingement heat transfer in cross-flow for all the cases, and its effect depends on the shape of the VGP, the height of the VGP, and also the cross-flow Reynolds number. The RW provides better heat transfer enhancement than the DW due to stronger vortical flow. The enhancement also increases monotonically with the height of the VGP. In addition, the averaged Nusselt number and pressure drop of the jet and cross-flow at different cross-flow Reynolds numbers are included. It is found that the favorable effects of the VGP are more significant as the cross-flow Reynolds number increases. Some PIV measurements were carried out. The flow structures and heat transfer mechanisms are discussed.