Some properties of generalized age-distribution equations in fluid dynamics (Q2706091)

From authors' summary: The concept of age in fluid dynamics is analyzed in the case of tracer advection-diffusion equation. From the general solution for a uniform velocity field, it is shown that unexpected symmetry properties arise for the age field. In particular, for a point release, the age field is isotropic, regardless of the direction of the flow and the value of diffusion coefficient. The analysis is then extended to situations with time-varying flows, where the symmetry can be broken under some circumstances. Finally, we present a method by which a time-dependent problem can be used to assess the stationary concentration distribution function, providing details about the propagation of younger and older materials at a given location.