Inertia-induced coherent structures in a time-periodic viscous flow

Three-dimensional advection of passive tracers in time-periodic viscous flows serves as model problem for laminar mixing. An important issue in this context is the response of invariant surfaces (typically tori or spheres) in thetracer-path topology that may occur in the non-inertial limit (Re=0) of such flows to fluid inertia (Re>0). These surfaces form transport barriers and their destruction (by e.g. inertia) is imperative for efficient mixing. Flows with invariant tori have been studied extensively; flows with invariant surfaces other than tori have not. Non-toroidal cases are likely in practice and may behave differently from the toroidal case, however. The presented study concerns a flow with spheroidal invariant surfaces and investigates the changes in topology during transition from a non-inertial state (inefficient mixing) towards an inertial state devoid of transport barriers (efficient mixing).