Non-axisymmetric shear layers in precessing fluid ellipsoidal shells

The motion of fluid in a slowly precessing ellipsoidal shell is calculated numerically. A novel spectral method is employed which uses a decomposition in spherical harmonics but enforces boundary conditions on oblate surfaces . Internal shear layers appear in the simulated flows either because the el lipticities of inner and outer boundaries differ, or because Ekman layers b reak down. The structure of these layers and their orientation with respect to the axis of precession depends on the relative magnitudes of pressure a nd viscous torques exerted by the boundaries on the fluid.