Early development of buoyant convection in porous media*

Vertical buoyancy-driven flows are usually termed as plumes. In porous media, plumes form when there is density gradient between two or more fluids, for example during groundwater contamination or carbon sequestration. Plumes have been studied theoretically to a large extent, but its evolution has not properly been analysed experimentally. Most studies in literature have focused on long-term behaviour assuming the plume to be fully developed. However, early time evolution of plumes is different from that in late times as the flow here is influenced equally by the transverse and longitudinal components of velocity and concentrations. We present light attenuation based table top experiments investigating the early development of plumes by changing the permeability of the medium and the density and flow rate of injection. We find that plumes initially form a blob shape, slowly turn into 'slightly elongated' and then eventually into 'fully elongated' shape. We quantify the time scales of transitions from one shape to the other as functions of the experimental variables. We also measure the length and volume of the plumes and find that they evolve as a power law on time.