Quantifying Mixing in Confined Stratified Aquifer Flows
Abstract
Spatial variability in a flow field leads to spreading of a transported tracer. The action of microdispersion is to smooth out any gradients that exist in the system. The combined effect of these two phenomena leads to an 'effective' enhanced mixing that can be asymptotically quantified by an effective dispersion coefficient (i.e. Taylor dispersion). Mixing plays a fundamental role in driving chemical reactions. However, at preasymptotic times it is considerably more difficult to accurately quantify these effects by an effective dispersion coefficient as spreading and mixing are not the same (but intricately related). Mixing can be characterized by the scalar dissipation rate. The latter measures the destruction of concentration variance and thus is an indicator for the degree of mixing of a system. We study preasymptotic solute mixing in terms of explicit analytical expressions for the scalar dissipation rate and numerical random walk simulations. Our results shed some new light on the mechanisms that lead to large scale mixing and allow for a distinction between solute spreading and mixing at preasymptotic times.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2009
- Bibcode:
- 2009AGUFM.H34D..05B
- Keywords:
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- 1829 HYDROLOGY / Groundwater hydrology;
- 1832 HYDROLOGY / Groundwater transport;
- 1869 HYDROLOGY / Stochastic hydrology