Abstract
The characteristics of large-scale coherent structures were investigated for a two-dimensional turbulent (Re=22000) jet undergoing self-sustained oscillations due to the interactions with the leading edge of a flat plate. The edge was placed 20 times the jet initial thickness away from the nozzle exit, x1/be=20. The flow in this geometry was characterized by periodic oscillations, or edgetone, whose length scale reaches a distance between nozzle and leading edge. The X-probe hot wire data were filtered and phase-averaged to discriminate the periodic velocity fluctuation components from the steady and the non-periodic components. The spatial distribution of the vorticity derived from the periodic velocity components indicate clearly the generation of large-scale coherent structures at the frequency of the jet oscillations. Each coherent structure, or a fluid volume with a correlated vorticity, increased monotonically its lateral extent and the maximum magnitude of vorticity in it, as it was transported toward the edge. The contribution of the periodic velocity flucutuations to the Reynolds stress and the turbulence energy production by far overweighed that of the non-periodic fiuctuations in 10≤x1/be≤30. The coherent structures indicated monotonic decay along the flat plate.
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