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| Titel |
Solute transport through a fracture with significant density effects and short of the asymptotic Taylor regime |
| VerfasserIn |
J. Bouquain, L. Michel, Y. Méheust, J.-P. Caudal, T. Le Borgne, J. de Bremond d'Ars, P. Davy |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250030603
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| Zusammenfassung |
| Contaminant transport in heterogeneous fractured aquifers occurs mostly through the
networks of intersecting fractures. Solute transport through individual fractures is often
studied considering a continuous inflow of solute. Here we investigate the spreading and
mixing of a finite amount of solute entering a fracture of constant aperture and with no
significant wall roughness. The shearing induced by contact conditions at the fracture
walls creates a dramatic spreading of the solute cloud, which is at the same time
broadened through micro-dispersion. After a long time, this process leads to the
well-known Taylor dispersion regime, in which the solute progresses along the fracture
according to a one-dimensional advection-dispersion equation, at an average velocity
identical to the average velocity of the fluid. In the configuration addressed by us, the
observation time ranges from the injection time to the time characteristic of the
asymptotic regime. We analyze solute concentration fields obtained either through
two-dimensional finite element simulations, or from data recorded on an analog
experimental setup, and characterize their longitudinal spreading in time, as well as
the solute mixing/dilution, using horizontal centered local second moments and
the corresponding horizontal effective concentration fields (following Dentz and
Carrera, Phys. Fluids, 19, 2007). The significant density/buoyancy effects present in
the experimental data are observed to delay the evolution towards the asymptotic
regime. Finite element numerical simulations in which flow- and transport- equations
are coupled through the relation between fluid buoyancy and solute concentration
provide an explanation to this experimental observation. Thus, buoyancy effects
impact solute transport in fracture even in the absence of fracture wall roughness. |
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