A Numerical Investigation of the Effects of Compositional and Thermal Buoyancy on Transient Plumes in a Porous Layer

Abstract

We present a suite of high-resolution numerical model experiments conducted to investigate the effects of varying thermal and compositional buoyancy on the behavior and morphology of plumes in porous media. The calculations model the injection of fluid through a narrow opening into the base of a nonreactive, saturated, porous matrix with interstitial fluid of different temperature and/or solute concentration and are scaled to be comparable with previously published experimental results. Calculations are presented for the case of zero injection velocity (in which case heat and solute diffuse in from the boundary) and for small, nonzero injection velocity. Different combinations of thermal and compositional buoyancies result in various plume structures owing to the fact that solute and heat both diffuse and advect at different rates in porous media. Plumes with dominantly positive thermal buoyancy have large plume heads, while those with dominantly compositional buoyancy lack this feature and propagate more rapidly. When the injected fluid has positive compositional and negative thermal buoyancy, the initial flow spreads laterally along the base of the domain before a narrow straight-sided compositional plume emerges. For cases when the injected fluid has positive thermal buoyancy and negative compositional buoyancy, plumes initially rise upward before a dense solute “cap” forms, interrupting the flow. For sufficiently large positive thermal buoyancy, this cap breaks down and the flow becomes highly time dependent. The velocities and widths of the plumes are also presented in order to characterize the plumes formed in the different parameter regimes.