Experimental studies of front propagation and mode-locking in an advection-reaction-diffusion system

Experiments are presented on reaction processes in a cellular, time-periodic fluid flow composed of a chain of oscillating vortices. Previous studies have shown that mixing of passive impurities in this flow is chaotic. Chemical fronts are studied in this flow using the excitable regime of the ruthenium-catalyzed Belousov-Zhabotinsky reaction. The velocities of the fronts are measured as a function of both the frequency and the amplitude of the external forcing. Arnol'd tongues are observed, where the propagating front mode-locks to the forcing, resulting in regimes where the front propagates an integer number of vortices in an integer number of drive periods. Overlapping of the tongues results in dual-locked behavior where the propagation velocity switches between two locked values