Frozen fronts in cellular flows

We present experiments showing that cellular flows often freeze the motion of chemical fronts in the presence of an opposing uniform wind. Fronts pin to the vortex structure in a chain of counter-rotating vortices for a wide range of imposed wind speeds that grows nonlinearly with the strength of the underlying vorticity. The same phenomenon is observed in a two-dimensional, spatially-disordered array of vortices, indicating that the ability to pin fronts is a general property of vortices. We further investigate the strength of the pinning with the addition of a time-periodic (oscillatory) wind, introducing chaotic advection and potential effects of mode-locking. These results demonstrate that any general theory of advection-reaction-diffusion dynamics will have to account for the tendency of cellular structures to pin fronts.