Spontaneous occurence of inertial waves in a rotating liquid metal flow.

The dynamics of free inertial waves inside a cylindrical volume was investigated experimentally in this study. The liquid metal GaInSn was chosen as fluid in order to enable a contactless stimulation of the flow inside the cylinder by means of a rotating magnetic field which generates a supercritical rotating motion of the liquid. The experiment demonstrates that inertial waves may be excited spontaneously by turbulent structures in the rotating flow. A prominent feature of our experimental configuration is the interaction between the inertial modes and the secondary flow arising from the Ekman transport. We observed the formation of inertial waves even without any external triggering in form of deliberate disturbances of the rotating flow field. The reason for such a spontaneous excitation of inertial waves can be explained by the existence of Taylor-Görtler vortices at the sidewall of the vessel. These TG-vortices are conveyed by the secondary flow towards the top and bottom of the vessel where they dissipate in the Bödewadt layer. Such a vortex dissipation in the Bödewadt layer leads to a perturbation of the Ekman pumping resulting in the excitation of an inertial wave.