Browsing by Subject "Advection"

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  • Afonso, M.M.; Mazzino, A.; Muratore-Ginanneschi, P. (2013)
    We perform an analytical study of the inertial-particle dynamics in the limit of small but finite inertia, in incompressible flows, exploring two specific issues. First, by means of a multiscale expansion, we analyse the particle effective diffusivity, and in particular its dependence on Brownian diffusivity, gravity and particle-to-fluid density ratio. We identify some cases of anomalous diffusion. Secondly, we investigate the concentration of particles continuously emitted from a point source with a given exit velocity distribution. The anisotropy of the latter turns out to be a necessary factor for the presence of a correction (with respect to the corresponding tracer case) at order square root of the Stokes number. In both cases, we obtain forced advection-diffusion equations for auxiliary quantities in the physical space, thus simplifying the problem from the full phase space to a system which can easily be solved numerically. Copyright © ETC 2013 - 14th European Turbulence Conference.All rights reserved.
  • Kuva, J.; Voutilainen, M.; Mattila, K. (2019)
    The time domain-random walk method was developed further for simulating mass transfer in fracture flows together with matrix diffusion in surrounding porous media. Specifically, a time domain-random walk scheme was developed for numerically approximating solutions of the advection-diffusion equation when the diffusion coefficient exhibits significant spatial variation or even discontinuities. The proposed scheme relies on second-order accurate, central-difference approximations of the advective and diffusive fluxes. The scheme was verified by comparing simulated results against analytical solutions in flow configurations involving a rectangular channel connected on one side with a porous matrix. Simulations with several flow rates, diffusion coefficients, and matrix porosities indicate good agreement between the numerical approximations and analytical solutions.