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Succession of resonances to achieve internal wave turbulence

We study experimentally the interaction of nonlinear internal waves in a stratified fluid confined in a trapezoidal tank. The set-up has been designed to produce internal wave turbulence from monochromatic and polychromatic forcing through three processes. The first is a linear transfer in wavelength obtained by wave reflection on inclined slopes, leading to an internal wave attractor which has a broad wavenumber spectrum. Second is the broad banded time-frequency spectrum of the trapezoidal geometry, as shown by the impulse response of the system. The third one is a nonlinear transfer in frequencies and wavevectors via triadic interactions, which results at large forcing amplitudes in a power law decay of the wavenumber power spectrum. This first experimental spectrum of internal wave turbulence displays a $k^{-3}$ behavior.