Three-dimensional physical benchmark experiments to test variable-density flow models
Flow and transport in saturated porous media may be influenced, or even dominated, by phenomena of variable-density flow, if solute concentration gradients are high. The numerical codes used for simulation of these situations have to be tested in order to ensure their reliability. A series of laboratory experiments with well-defined experimental parameters for a typical variable-density problem were performed to provide data for such a test. A Nuclear Magnetic Resonance Imaging technique was used, which was appropriate for measuring the three-dimensional salt concentration distribution in a porous medium, including its evolution with time. Two experiments were conducted with 1 and 10% salt mass fraction as initial salt concentration contrasts. These key experiments were accompanied by supplementary ones to determine experimental parameters and to check the behaviour for intermediate initial salt concentrations. The set-up involved a stable layering of the saltwater below freshwater, affected by recharge and discharge of water at the top. The situation is comparable to the upconing of a saltwater-freshwater interface due to pumping. Numerical simulations were performed with a variable-density flow code and the results compared with those from the laboratory experiments. Finally, it is illustrated how these experimental data can be used as a benchmark test for variable-density flow models.
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