Wave turbulence

By using a stereoscopic imaging technique, we could obtain a space-time resolved measurement of wave turbulence at the surface of water in a 13-m diameter tank. Wave are excited by meter-sized wedge wave makers that are close to omnidirectional. A frequency-wavenumber analysis shows that a turbulent regime develops that is made of a superposition of free waves and bound waves as expected for gravity surface waves. These bound waves result from triadic nonlinear interaction that provide energy to Fourier modes that are not lying on the linear dispersion relation (and thus non resonant). By performing a filtering in the Fourier space, we can remove the bound wave contribution to keep only the free wave one and we show, first, that the observed weak turbulence is indeed weakly nonlinear and, second, that the filtered field is much closer to Gaussian statistics. Furthermore the observed intermittency is strongly reduced so that the free-wave field is close to Gaussian at all scales.

Wave turbulence occurs in various domains of physics (plasma physics, elasticity, or fluid mechanics) but is far to be completely understood, notably for ocean surface waves. By using a large-diameter centrifuge, we are able to tune the gravity field up to 20 times the Earth acceleration. This new technique then allows us to report the first observation of gravity wave turbulence on the surface of a fluid in hyper-gravity environment. This is also a unique solution to significantly expands the inertial range of gravity wave turbulence in laboratory. Wave turbulence properties are then reported as function of the gravity level, and we show that the usual energy transfer by nonlinear wave interactions are modified by large-scale container modes.