Flow-field characteristics of a synthetic jet impinging on a circular cylinder in a free and constrained environment

Abstract

The flow field of a synthetic jet (SJ) impinging on a circular cylinder has been investigated while varying jet-cylinder separation distances in a free and constrained environment. For the free environment case, the cylinder was placed in the SJ flow field in a quiescent environment, and its separation distance downstream from the slot exit was varied. Whereas for the constrained environment case, two parallel sidewalls were mounted along the shorter side of the slot, and the cylinder was placed between these sidewalls. The slot width (w = 6.4 mm) and aspect ratio (25) were kept constant for both cases. The experimental results for the SJ impinging on a circular cylinder showed that the flow-field behavior differs significantly from that of a cylinder in uniform flow and is largely affected by the jet-cylinder separation distance and the operating environment, i.e., free or constrained. The plots of the pressure distribution and normalized standard deviation of the fluctuating pressure around the cylinder surface revealed higher flow fluctuations associated with SJ impingement. The flow visualization and the hot wire measurements further unveiled that no obvious vortex shedding occurs in the cylinder wake. However, evidence for vortex dipoles rising from the cylinder surface was found, on either side of the cylinder (perpendicular to the flow direction).