Experimental studies of pinned and unpinned reaction fronts in two-dimensional, vortex-dominated flows

We present experiments that study the propagation and pinning of reaction fronts in laminar, two-dimensional fluid flows. The flows are forced using magnetohydrodynamic techniques and are composed of vortex chains and arrays with or without an imposed wind. The reaction fronts are produced by the excitable, ferroin-catalyzed Belousov-Zhabotinsky chemical reaction. We consider how the addition of time-periodic oscillations of the flow can affect the pinning of reaction fronts.\footnote{P.W. Megson, M.L. Najarian, K.E. Lilienthal and T.H. Solomon, Phys. Fluids {\bf 27}, 023601 (2015).} Furthermore, we measure the speed at which reaction fronts propagate in the flow, looking for scaling of the measured front propagation speed with the non-dimensional reaction-diffusion (no flow) speed. We analyze all of these results by considering the role of one-way barriers produced by ``burning invariant manifolds.''\footnote{J. Mahoney, D. Bargteil, M. Kingsbury, K. Mitchell and T. Solomon, Europhys. Lett. {\bf 98}, 44005 (2012).}