Disorder-Induced Capillary Bursts Control Intermittency in Slow Imbibition

A multiscale analysis of the spatially averaged velocity of an imbibition front V-l(t) measured at scale l reveals that the slow front dynamics is intermittent: the distributions of Delta V-l(tau) = V-l(t+tau) - V-l(t) evolve continuously through time scales tau, from heavy-tailed to Gaussian-reached at a time lag tau(c) set by the extent of the medium heterogeneities. Intermittency results from capillary bursts triggered from the smallest scale of the disorder up to the scale l(c) at which viscous dissipation becomes dominant. The effective number of degrees of freedom of the front l/l(c) controls its intensity.