Nonlinear spin-up of a rotating stratified fluid: Theory

We consider the boundary layer that forms on the wall of a relating contain er of stratified fluid when altered from an initial state of rigid body rot ation. The container is taken to have a simple axisymmetric form with slopi ng walls. The introduction of a non-normal component of buoyancy into the v elocity boundary-layer is shown to have a considerable effect for certain g eometries. We introduce a similarity-type solution and solve the resulting unsteady boundary-layer equations numerically for three distinct classes of container geometry. Computational and asymptotic results are presented for a number of parameter values. By mapping the parameter space we show that the system may evolve to either a steady state, a double-structured growing boundary-layer or a finite-time breakdown depending on the container type, rotation change and stratification. In addition to extending the results o f Duck et al. (1997) to a more general container shape, we present evidence of a new finite-time breakdown associated with higher Schmidt numbers.