Diffusion of Heat as a Passive Contaminant in a Slightly Pulsating jet
Results on the diffusion of a passive contaminant (heat) by a round jet subjected to small amplitude periodic forcing at the frequency of the preferred mode are presented. The instantaneous isotherm pattern show the growth of coherent structures in the mixing layer from the nozzle to a distance 3d0 downstream. The temperature in the core of these structures is approximately uniform whereas on both sides of the mixing layer a sharp temperature gradient gives rise to intense θ- fluctuations. The structures begin to lose their coherence beyond 3d0 and are partially blurred by the turbulence which is developing. It is nevertheless observed that the structures convected downstream have a strong influence on the temperature on the jet axis. The isotherms are slowly stretched and then rapidly compressed during a cycle. Hot fluid is ejected outwards from the axis on the leading edge of the structures and cold fluid is trapped inwards on the trailing edge.
KeywordsVortex Coherence Settling
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