Finite-size effects in parametric subharmonic instability

Baptiste Bourget (1) , Hélène Scolan (1) , Thierry Dauxois (1) , Michael Le Bars (2) , Philippe Odier (1) , Sylvain Joubaud (1)

1 Phys-ENS - Laboratoire de Physique de l'ENS Lyon
2 IRPHE - Institut de Recherche sur les Phénomènes Hors Equilibre

The parametric subharmonic instability in stratified fluids depends on the frequency and the amplitude of the primary plane wave. In this paper, we present experimental and numerical results emphasizing that the finite width of the beam also plays an important role on this triadic instability. A new theoretical approach based on a simple energy balance is developed and compared to numerical and experimental results. Because of the finite width of the primary wave beam, the secondary pair of waves can leave the interaction zone which affects the transfer of energy. Experimental and numerical results are in good agreement with the prediction of this theory, which brings new insights on energy transfers in the ocean where internal waves with finite-width beams are dominant.

Domaines: Dynamique des Fluides [physics.flu-dyn]; Mécanique des fluides [physics.class-ph]; Mécanique des fluides [physics.class-ph]; Océan, Atmosphère

Baptiste Bourget, Hélène Scolan, Thierry Dauxois, Michael Le Bars, Philippe Odier, et al.. Finite-size effects in parametric subharmonic instability. Journal of Fluid Mechanics Digital Archive, 2014, 759, pp.739-750. ⟨10.1017/jfm.2014.550⟩. ⟨ensl-01064683⟩