Abstract
Internal waves generated by the turbulent wake of a sphere travelling horizontally through a linearly stratified fluid were studied using shadowgraph and particle-streak photography. The Reynolds and internal Froude number ranges considered were 2,000 ≤ Re ≤ 12,900 and 2.0 ≤ Fi ≤ 28.0, respectively. Two quite distinct flow regimes based on the structure of the turbulent wake were identified. In one, the wake is characterized by “large-scale coherent structures”. In the other, the wake, as viewed on a side-view shadowgraph, grows in a roughly symmetric fashion to a maximum height and then collapses slowly; such flows are termed the “smallscale structures” regime.
Wave lengths and maximum wave heights of the internal waves were measured as functions of Nt and Fi, where N is the Brunt-Väisälä frequency and t the time. It was found that the wave lengths scale well with the streamwise dimension of the spiralling coherent structures. The maximum amplitude of the internal waves were found to scale with the vertical dimension of the turbulent wake, upon varying the internal Froude number.
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Lin, Q., Boyer, D.L. & Fernando, H.J.S. Internal waves generated by the turbulent wake of a sphere. Experiments in Fluids 15, 147–154 (1993). https://doi.org/10.1007/BF00190954
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DOI: https://doi.org/10.1007/BF00190954