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Experimental investigation of double-diffusive groundwater fingers

Published online by Cambridge University Press:  21 April 2006

Paul T. Imhoff  and
Theodore Green
Paul T. Imhoff
Affiliation:
Department of Civil Engineering, Princeton University, Princeton, NJ 08544, USA
Theodore Green
Affiliation:
Department of Civil and Environmental Engineering, University of Wisconsin, Madison, WI 53706, USA
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Abstract

Using a sand-tank model and the salt-sugar system, double-diffusive fingers formed in a saturated porous medium. In contrast to the quasi-steady fingering typically observed in a viscous fluid, the fingering here was quite unsteady. The fingers’ structure was observed, and measurements of the sugar flux indicate that double-diffusive groundwater fingers can transport solutes at rates as much as two orders of magnitude larger than those associated with molecular diffusion in motionless groundwater. The buoyancy-flux ratio, r = αFT/βFS, increased from r = 0.65 ± 0.02 (at Rρ = 1.02) to r = 0.81 ± 0.06 (at Rρ = 1.50), where Rρ is the density-anomaly ratio. (Using the salt-sugar system in a viscous fluid, r was previously shown to decrease with increasing Rρ.) The buoyancy flux due to sugar varied approximately as R−5.6ρ, which is almost identical with the variation found for salt-sugar fingers in a viscous fluid. The model of Green (1984) was applied to the experiments and predicted buoyancy-flux ratios and finger widths that were in fairly good agreement with the measured values, although the predicted buoyancy fluxes due to sugar were significantly larger than the measured fluxes.

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 188 , March 1988 , pp. 363 - 382
Copyright
© 1988 Cambridge University Press

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