title: Stretching, coalescence, and mixing in porous media.
abstract: We study scalar mixing in heterogeneous conductivity fields, whose structural disorder varies from weak to strong. A range of stretching regimes is observed, depending on the level of structural heterogeneity, measured by the log-conductivity field variance. We propose a unified framework to quantify the overall concentration distribution predicting its shape and rate of deformation as it progresses toward uniformity in the medium. The scalar mixture is represented by a set of stretched lamellae whose rate of diffusive smoothing is locally enhanced by kinematic stretching. Overlap between the lamellae is enforced by confinement of the scalar line support within the dispersion area. Based on these elementary processes, we derive analytical expressions for the concentration distribution, resulting from the interplay between stretching, diffusion, and random overlaps, holding for all field heterogeneities, residence times, and Péclet numbers.
authors.affiliation: Geosciences Rennes, UMR 6118, Université de Rennes 1, CNRS, 35042 Rennes, France.
authors.forename: Tanguy
authors.initials: T
authors.lastname: Le Borgne
authors.affiliation: Spanish National Research Council (IDAEA-CSIC), 08034 Barcelona, Spain.
authors.forename: Marco
authors.initials: M
authors.lastname: Dentz
authors.affiliation: Institut de Recherche sur les Phénomènes Hors Equilibre, Aix-Marseille Université, 13384 Marseille Cedex 13, France.
authors.forename: Emmanuel
authors.initials: E
authors.lastname: Villermaux