Session EN - Geophysical Fluid Dynamics II.
ORAL session, Monday morning, November 24
Preakness, SMH
This paper concerns the elliptical instability of a flow in a rotating deformed sphere. The aim of our work is to experimentally analyse the characteristics of this instability and to provide a theoretical model which accounts for the observations. For this purpose, an elastic and transparent hollow sphere has been moulded in a silicone gel block. The flow is visualised using Kalliroscope flakes illuminated with a laser sheet as the sphere is set into rotation and compressed by two rollers. The elliptical instability occurs by the appearance of the so-called 'spin-over' mode whose growth rate and saturation amplitude are measured by video image analysis at different Ekman numbers. Growth rates are shown to be well predicted by the linear stability analysis. A nonlinear model is developed and shown to correctly describe the saturated regimes observed in the experiments. At low Ekman numbers, a secondary instability leading to an intermittent regime is also discovered.