Numerical and experimental analysis of the flow and transition of free synthetic jets

Abstract

In this paper, flow characteristics and the transition of synthetic jets are investigated numerically and experimentally. The investigated synthetic jets have a dimensionsless stroke length L-0/d of 146 and 167, an U-0 of 7.3 and 8.35 m s(-1) and a jet Reynolds number Re-U0 of 471 and 539. Novelty of this paper is the extensive analysis and explanation of why synthetic jets with L-0/d > 70 result to transition and turbulent flow: it is shown that the jets exhibit swirl which originates from the cavity. The rotation results in more rapid divergence and deceleration of the free jets. Both processes initially cause disruptions of the primary vortex and the secondary vortices, also vortex breakdown, and ultimately result in jet turbulence. Extension of the laminar region spatially and temporally is possible by increasing the height of the cavity.