Effectiveness of stirring measures in an axisymmetric rotating annulus flow

Lagrangian stirring in a thermally driven rotating annulus is investigated numerically using a Navier-Stokes model and a second order Runge-Kutta integration routine. The stirring properties are investigated using finite scale Lyapunov exponents, Lagrangian coherent structures and a leaking method. The ability of these measures to identify transport barriers, regions of well and poorly stirred flow, and stable and unstable manifolds is investigated, as well as the stirring properties of the annulus flow. It is found that finite scale Lyapunov exponents characterise the stirring properties of flows occurring in the rotating annulus more efficiently than the leaking method or Lagrangian coherent structures. The strength of the stirring varies monotonically with thermal forcing amplitude, but non-monotonically with forcing frequency. The flows investigated are axisymmetric (i.e. two dimensional) and time dependent.