Physics of the cigarette filter: fluid flow through structures with randomly-placed obstacles

This talk briefly reviews the subject of fluid flow through disordered media. In particular, we focus on the sorts of considerations that may be necessary to move statistical physics from the description of idealized flows in the limit of zero Reynolds number to more realistic flows of real fluids moving at a nonzero velocity, where inertia effects mean that dangling ends are explored and the backbone is not entirely explored by the fluid. We discuss several intriguing features, such as the surprisingly sharp change in behavior from a localized to delocalized flow structure (distribution of flow velocities) that seems to occur at a critical value of Re which is orders of magnitude smaller than the critical value of Re where turbulence sets in.