Numerical Investigation of Vortical Structures and Heat Transfer in Elliptic Impinging Synthetic Jets

This study aims to understand the mechanism by which vortices influence heat transfer in noncircular impinging jets. Large-eddy simulations are conducted for elliptic impinging synthetic jets with orifice aspect ratios of 3 and 5, compared to a circular case at a constant wall temperature and orifice-to-wall distance. The elliptic cases exhibit different heat transfer characteristics from the circular case because of their unique vortex–wall interactions. During the stage of strong vortex–wall interactions, in the major axis plane, the primary vortex ring moves closer to the wall and strengthens by merging with an arc-shaped vortex. In the minor axis plane, the arc-shaped vortex impinges on the wall much earlier and becomes stronger. These indicate stronger downwash and deeper penetration of the thermal boundary layer in the elliptic cases. During the stage of the vortex ring spreading, heat transfer is influenced by vortex interactions. In the circular case, heated fluid undergoes re-entrainment along with the secondary/tertiary vortices from the wall back to the jet flow, resulting in a decrease in local heat transfer. However, this effect diminishes in elliptic jets. Based on these flow characteristics, the elliptic cases effectively improve the instantaneous heat transfer and produce much larger time-averaged heat transfer areas.