Vortex-wall interactions in elliptic impinging synthetic jets

Vortex structures and flow scenarios of noncircular vortex rings impinging onto walls were studied by conducting a large eddy simulation. Three orifice aspect ratios, ARs = 3, 5, and 7, and six dimensionless orifice-to-wall distances, in the range H = 0.71-1.90, were considered for elliptic impinging synthetic jets. At H = 0.95-1.19, the results exhibit different flow scenarios from those of circular vortex rings, which directly interact with the wall to produce a secondary vortex ring. New scenarios are attributed to mutual interactions between the primary vortex ring, the arc-shaped vortex, the wall, and the arc-shaped vortex is unique to noncircular vortex rings. These scenarios are further divided into two categories depending on whether the primary vortex ring can merge with the arc-shaped vortex, which is strongly affected by their separation distance and circulation ratio at the onset of vortex-wall interactions. For small separation distance and circulation ratio, the primary vortex ring swallows the arc-shaped vortex, leading to a strong crescent-shaped secondary vortex or a secondary vortex ring at different ARs. However, as the separation distance or circulation ratio increases, the interactions between the primary vortex ring and arc-shaped vortex weaken so that the latter escapes from entrainment by the primary vortex ring, leading to a weak crescent-shaped vortex. Finally, an AR-H map is constructed to illustrate the flow scenarios for all the cases. These findings provide new insights into the intricate dynamics of noncircular ring-wall interactions and may help us understand the heat transfer performance of noncircular impinging synthetic jets.