Preliminary identification of flow regimes in a mechanically oscillated planar jet

Abstract

A plate with a large aspect ratio nozzle was mechanically oscillated in a near sinusoidal fashion with three ratios of oscillation stroke to nozzle diameter, namely 10, 5 and 2.5. A set of 210 different flow conditions was investigated in the laminar Reynolds number regime and visualized utilizing both the hydrogen bubble and dye trace technique. Three flow regimes were identified with the transition between them being dependent on a Strouhal number based on oscillation stroke, which is equivalent to a relative velocity ration of the plate to the jet [V]/U. The first regime identified occurs in the highset velocity ratio region and has been termed the Wall Vortex regime. Here a vortex detaches from the jet at the end of each stroke and stays attached to the plate. A second flow regime, termed the Mushroom Vortex regime exists at lower velocity ratios. Here a counter-rotating vortex pair forms within the jet at the end of each stroke. The third regime is called the Weaving Jet regime. There the jet is ejected approximately normal to the plate but exhibits large-scale oscillations further downstream. All regimes were recorded and half sequences are presented here.