A three-dimensional physical model for verification of variable-density flow codes

Flow and transport in saturated porous media are influenced or even dominated by the effects of density flow if solute concentration gradients are high. The numerical codes used in the simulation of these nonlinear phenomena have to be tested in order to ensure their reliability. A series of laboratory experiments with well-defined experimental parameters for two typical variable-density flow problems were performed to obtain the data required for benchmarking. A Nuclear Magnetic Resonance Imaging technique was used to measure the three-dimensional salt concentration distribution in a porous medium, including its time evolution. The first problem studied was an unstable density layering of denser saltwater above less dense freshwater, and the onset of finger instabilities was observed. The second case was a stable layering of saltwater below freshwater influenced by discharge of water at the top and resulting in a time-dependent upconing. Numerical simulations of the problems were performed with three different variable-density flow codes and compared with the experimental results.