Many flows feature a strong vorticity: tornadoes, hurricanes, aircraft wakes ... Vortices also play a key role in the energy cascade of classical and quantum turbulence. Kelvin waves are elementary perturbations of such vortices - helical waves propagating along the vortex line.
Many theoretical works have predicted their behaviour but no experimental confirmation has been reported so far.
By designing an original experimental set up, consisting in a bathtub vortex without rotation of the tank, we measured the Kelvin wave dispersion relation, with good resolution, for the first time. Their spectral signature is very rich and includes several wave modes. They all match the theoretical predictions.
We then turn to investigating Kelvin wave turbulence - a phenomenon carrying energy towards small scales through nonlinear wave interactions.
It paves the way to the experimental study of solitons and the dynamics of an array of vortices, whose collective motion is known as 'Tkachenko waves'.
By Geoffrey Vallis
By Luca Melzi
By Beatrice Pelloni
