Scattering by Source-Type Flows in Disordered Media

Scattering through natural porous formations (by far the most ubiquitous example of disordered media) represents a formidable tool to identify effective flow and transport properties. In particular, we are interested here in the scattering of a passive scalar as determined by a steady velocity field which is generated by a line of singularity. The velocity undergoes to erratic spatial variations, and concurrently the evolution of the scattering is conveniently described within a stochastic framework that regards the conductivity of the hosting medium as a stationary, Gaussian, random field. Unlike the similar one for uniform (in the mean) flow-fields, the problem at stake results much more complex. Central for the present study is the fluctuation of the driving field, that is computed in closed (analytical) form as large time limit of the same quantity in the unsteady state flow regime. The structure of the second-order moment X_rr, quantifying the scattering along the radial direction, is explained by the rapid change of the distance along which the velocities of two fluid particles become uncorrelated. Moreover, two approximate, analytical expressions are shown to be quite accurate into reproducing the full simulations of X_rr. Finally, the same problem is encountered in other fields, belonging both to the classical and to the quantum physics. As such, our results lend themselves to be used within a context much wider than that exploited in the present study.