Coupled continuous-time random walks for fluid stretching in two-dimensional heterogeneous media

We study the relation between flow structure and fluid deformation in steady flows through two-dimensional heterogeneous media, which are characterized by a broad spectrum of stretching behaviors, ranging from sub- to superlinear. We analyze these behaviors from first principles, which uncovers intermittent shear events to be at the origin of subexponential stretching. We derive explicit expressions for Lagrangian deformation and demonstrate that stretching obeys a coupled continuous-time random walk, which for broad distributions of flow velocities becomes a Lévy walk. The derived model provides a direct link between the flow and deformation statistics, and a natural way to quantify the impact of intermittent shear events on the stretching behavior. © 2016 American Physical Society.MD acknowledges the support of the European Research Council (ERC) through the project MHetScale (contract number 617511). TLB acknowledges Agence National de Recherche (ANR) funding through the project ANR-14-CE04-0003-01.Peer reviewe