A NUMERICAL STUDY ON GRAVITATIONAL INSTABILITIES OF DENSE AQUEOUS-PHASE PLUMES IN 3-DIMENSIONAL POROUS-MEDIA

Variations in the density of aqueous phase fluids flowing in a porous medium, resulting from spatial and temporal variations in the solute c oncentration, often gives rise to unstable flow and mixing. Numerical studies on unstable behavior of dense aqueous phase contaminant plumes in three-dimensional porous media are rare in the literature. In this study, a three-dimensional numerical model was used to simulate gravi tational instabilities in dense aqueous phase plumes. Our simulated re sults showed that physically realistic instabilities in dense plumes c an be generated by small random perturbations, including truncation/ro und-off errors. Although the numerical simulations were able to qualit atively reproduce the experimental results, they quantitatively undere stimated unstable behavior of dense plumes. For a given size of the co ntaminant source, the width of the porous medium had a significant eff ect on the occurrence and development of gravitational instabilities. Dense plumes are more unstable in the transverse than in the longitudi nal direction of the flow domain.