Azimuthal flow associated with inertial wave resonance in a precessing cylinder

A series of experiments has been carried out on low-viscosity fluid in a right-circular cylinder that rotates rapidly at a constant speed about its axis of symmetry. This axis in turn is made to undergo less rapid precession about a second axis passing through the centroid of the cylinder. The linear inviscid response of the fluid to such forcing can be expressed as a spectrum of inertial wave modes. However, there are several interesting features of the problem that are associated with nonlinear and viscous effects. One such phenomenon is the appearance of an azimuthal flow under conditions that are related to the underlying linear inertial wave behaviour. Results are presented concerning the manner in which this flow depends on the various experimental parameters. Dynamical properties of the circulation following the onset of forcing have also been investigated. The flow at forcing frequencies close to the fundamental inertial wave resonance was found to have a vortex-like structure, and this led to data that suggest that hydrodynamic instabilities may play a part in the observed breakdown to turbulent motion in regimes of strong forcing.