Vortex–wall interactions in elliptic impinging synthetic jets

Abstract

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.