Internal waves generated by a translating and oscillating sphere
Dupont, Pascal ; Voisin, Bruno
At high Reynolds and Froude numbers, lee waves owing to the horizontal motion of a body in a stratified fluid are superseded by random waves generated by its wake. The origin of these waves lies in the buoyant collapse of the large-scale coherent structures of the wake, and can be modelled as a source moving at the velocity of the body and of strength oscillating at the frequency of vortex shedding. In the present paper two parallel studies of the associated wavefield are described. The first of these is theoretical and considers localized and extended models of the source, while the second is experimental and involves a vertically oscillating and horizontally translating sphere. Oscillation frequencies both smaller and larger than the Brunt-Väisälä frequency are considered, and reasonably good agreement between theory and experiment is obtained concerning, e.g. the shape of the surfaces of constant phase, the streamwise evolution of the wavelength, and the domain of existence of the waves. Calculations are then presented for a realistic turbulent wake, and comparison with available experimental results is performed.</p>
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