Experimental studies of reactions and front propagation in laminar fluid flows

We present studies of the effects of vortex-dominated fluid flows on the dynamics of the oscillatory or excitable Belousov-Zhabotinsky reaction. The results of these experiments have applications for advection-reaction-diffusion dynamics in a wide range of systems including microfluidic chemical reactors, cellular-scale processes in biological systems, and blooms of phytoplankton in the oceans. Much of our work is focused on understanding how reaction fronts propagate in fluid flows. To analyze and predict the behavior of the fronts, we generalize tools developed to describe passive mixing. In particular, the concept of an invariant manifold is extended to account for reactive burning. These ``burning invariant manifolds'' (BIMs) are barriers that locally block the motion of reaction fronts. Unlike invariant manifolds for passive transport, however, the BIMs are barriers for front propagation in one direction only. These ideas are tested and illustrated experimentally in two-dimensional flows composed of a chain of alternating vortices, a spatially-random flow, and vortex flows with imposed winds. We are also extending these studies to three-dimensional flows.