 |
| Titel |
Vorticity and upscaled dispersion in 3D heterogeneous porous media |
| VerfasserIn |
Mariaines Di Dato, Gabriele Chiogna, Felipe de Barros, Alberto Bellin, Aldo Fiori |
| Konferenz |
EGU General Assembly 2015
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250104135
|
| Publikation (Nr.) |
 EGU/EGU2015-3560.pdf |
|
|
|
|
|
| Zusammenfassung |
| Modeling flow in porous media is relevant for many environmental, energy and industrial
applications. From an environmental perspective, the relevance of porous media flow
becomes evident in subsurface hydrology. In general, flow in natural porous media is
creeping, yet the large variability in the hydraulic conductivity values encountered in natural
aquifers leads to highly heterogeneous flow fields. This natural variability in the
conductivity field will affect both dilution rates of chemical species and reactive mixing. A
physical consequence of this heterogeneity is also the presence of a various localized
kinematical features such as straining, shearing and vorticity in aquifers, which will
influence the shape of solute clouds and its fate and transport. This work aims in
fundamentally characterizing the vorticity field in spatially heterogeneous flow fields as a
function of their statistical properties in order to analyze the impact on transport
processes. In our study, three-dimensional porous formations are constructed with an
ensemble of N independent, non-overlapping spheroidal inclusions submerged into an
homogeneous matrix, of conductivity K0. The inclusions are randomly located in
a domain of volume W and are fully characterized by the geometry of spheroid
(oblate or prolate), their conductivity K (random and drawn from a given probability
density function fκ), the centroid location ¯x, the axes ratio e, the orientation of
the rotational axis (α1,α2) and the volume w. Under the assumption of diluted
medium, the flow problem is solved analitically by means of only two parameters: the
conductivity contrast κ = K/K0 and the volume fraction n = Nw/W . Through
the variation of these parameters of the problem, it is possible to approximate the
structure of natural heterogeneous porous media. Using a random distribution of the
orientation of the inclusions, we create media defined by the same global anisotropy
f = Iz/Ix but different micro-structure (inclusion’s type and shape). The purpose of this
work is to study how different micro-structures impact the vorticity. The analysis is
carried on for a binary medium, as a function of conductivity contrast κ, and for
heterogeneous ensemble of inclusions with a lognomal distribution of κ, as a function of
heterogeneity degree Ïăln κ2. Inclusion’s type and shape have a great influence on the
vorticity field: in media defined by the same volume fraction and anisotropy degree,
thinner inclusions yield more vorticity, therefore the smaller is e the greater is the
vorticity. This effect is more evident if inclusions are more conductive, due to flow
focusing effects. We demonstrate that the statistical anisotropy of the medium plays an
important role: the smaller is the statistical anisotropy ratio, the higher is the vorticity
produced by the mixture of inclusions. Furthermore, considering heterogeneous
mixture of inclusions, it is showed that vorticity growths with increasing the variance
of the conductivity contrast distribution. In addition to analyzing the rotational
properties of the spatially variable flow field, we illustrate how the global vorticity of the
medium affects solute transport. This is achieved by evaluating the upscaled dispersion
coefficients. |
|
|
|
|
|
|