Chaotic advection in a complex annular geometry

The dynamics of Lagrangian particles in a complex geometry is studied, both experimentally and through a full numerical simulation of the Navier-Stokes equations. The geometry is an annulus whose walls can be rotated independently. Stationary cylindrical rods can be positioned within the annulus in several arrangements. A variety of heteroclinic orbits are found at low Reynolds numbers, where the fluid flow is steady. As the flow becomes unsteady to a time-periodic (two-dimensional) state, it spontaneously gives rise to heteroclinic tangles that provide the organizing structure for the chaotic motion of fluid particles.