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

Marco Dentz (1) , Daniel R. Lester (2) , Tanguy Le Borgne (3) , Felipe P.J. de Barros (4)

1 IDAEA - Institute of Environmental Assessment and Water Research
2 RMIT University - Royal Melbourne Institute of Technology University
3 GR - Géosciences Rennes
4 Sonny Astani Department of Civil and Environmental Engineering

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.

Domains: Fluid mechanics [physics.class-ph]

Marco Dentz, Daniel R. Lester, Tanguy Le Borgne, Felipe P.J. de Barros. Coupled continuous-time random walks for fluid stretching in two-dimensional heterogeneous media. Physical Review E , 2016, 94 (6), pp.061102(R). ⟨10.1103/PhysRevE.94.061102⟩. ⟨insu-02442398⟩