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.
- CYLINDRICAL CAVITY