Internal wave generation by turbulent wakes
Résumé
At high Froude and Reynolds numbers, lee waves generated by a body moving horizontally in a stratified fluid give way to ‘random’ internal waves generated by the turbulent wake. This paper considers the second type of waves, whose presence is attributed to the collapse of vortex loops or turbulent bursts, associated with the coherent vortex structures of the wake. A simple analytical model of the collapse is given, leading to two distinct analyses of the waves. At moderate cross-stream distances the individual effect of each loop or burst is observed; waves have the same structure as for an isolated impulsive point source. At large cross-stream distances the collective effect of the loops or bursts is observed; waves reduce to those generated by a source of mass moving with the body, and emitting fluid at the frequency of vortex shedding and at some of its harmonics. Here, only the fundamental frequency is taken into account, in which case the waves decompose into several systems and are confined within conical caustics. All of this agrees with available experimental results. More attention is finally paid to the shape of surfaces of constant phase.
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