Internal wave structure emitted by a horizontally oscillating sphere

Evgeny V. Ermanyuk (1) , Jan-Bert Flór (2) , Bruno Voisin (2)

1 LIH - Lavrentyev Institute of Hydrodynamics
2 LEGI - Laboratoire des Écoulements Géophysiques et Industriels [Grenoble]

An oscillating body in a stratified fluid generates a double cone-shaped internal-wave pattern, the 3D analogue of the classic St.Andrew-cross. For sufficiently low frequency and large amplitude oscillations, higher-order wave harmonics may be generated along with the fundamental one. We present an experimental study of the 3D structure of first- and second-order wave fields emitted by a horizontally oscillating sphere. In contrast to the axisymmetric wave pattern found for a vertically oscillating sphere, for horizontal oscillations, the first- and higher-order-harmonic waves have different distributions of wave amplitudes in the azimuthal direction. The amplitude of the first-order waves is shown to follow the cosine dependence on the azimuthal angle, in accordance with theoretical predictions. The azimuthal distribution of the amplitude of the second-order waves gives evidence of a quadrupolar distribution, with four preferential directions of wave radiation in a horizontal plane, along the direction of oscillation and normal to it. Noteworthy is that the amplitudes of these second-order waves may exceed the amplitude of first-order waves.

Domaines: Mécanique des fluides [physics.class-ph]; Mécanique des fluides [physics.class-ph]

Evgeny V. Ermanyuk, Jan-Bert Flór, Bruno Voisin. Internal wave structure emitted by a horizontally oscillating sphere. 62nd Annual Meeting of the APS Division of Fluid Dynamics, Nov 2009, Minneapolis, United States. ⟨hal-00583103⟩