Results are Presented from an experimental study of fluid in a rotating cylinder which was subjected to precessional forcing. The primary objective was to determine the validity of the linear and inviscid approximations which are commonly adopted in numerical models of the problem. A miniature laser Doppler velocimeter was used to make quantitative measurements of the flow dynamics under a variety of forcing conditions. These ranged from impulsive forcing to continuous forcing at the fundamental resonance of the system. Inertial waves were excited in the fluid in each case, with the extent of nonlinear behaviour increasing from one forcing regime to the next. Good agreement was found with the predictions of linear theory in the weaker forcing regimes. For stronger forcing, it was possible to determine the approximate duration of linear behaviour before the onset of nonlinear dynamics. Viscous effects were found to be relatively weak when the frequency of precessional forcing was away from resonance. However, there was evidence of strong boundary-layer phenomena when conditions of resonance were approached.

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.

We report the results of an experimental and numerical study of the creation of stagnation points in a rotating cylinder of fluid where one endwall is rotated. Good agreement is found with previous results where the stagnation points are formed on the free core of the primary columnar vortex. The effect of adding a small cylinder along the center of the flow is then investigated and the phenomena are found to be robust despite the qualitative change in the boundary conditions. Finally, we show that sloping the inner cylinder has a dramatic effect on the recirculation such that it can either be intensified or suppressed.