Plumes and gravity currents are primarily vertical and horizontal flows, respectively, and driven due to buoyancy/density differences between two fluids. In porous media, such flows occur during carbon
sequestration, geothermal energy recovery or contaminant transport in groundwater. Density-driven flows, in general, result in mixing between the fluids due to molecular diffusion, however, in porous media the mixing gets enhanced due to mechanical dispersion caused by tortuous paths. Here we examine the effects of mechanical dispersion on the density and buoyancy-driven flows in porous media.Gravity currents in porous media have been studied extensively with an assumption that a sharp interface exist between the gravity current and ambient fluid, meaning that no mixing occurs between the two fluids.However, based on our laboratory experiments we demonstrate otherwise that a sharp interface model is inconsistent because, in reality, mixing occurs. Moreover, the scale of mixing gets enhanced significantly when the medium is heterogeneous. Motivated from the experimental findings, we also derive new theoretical results for modelling gravity current flows in porous media and associated mixing.
On the other hand, theoretical models for mixing in plumes already exist in literature, however, they only consider the effects of molecular diffusion. Given the high Peclet number in majority of subsurface flows, mechanical dispersion is usually dominant over molecular diffusion. We derive a new similarity solution for plumes in porous media and show that the rate of entrainment from ambient to the plume is several order greater in magnitude than that predicted by previous models using molecular diffusion. We verify our analytical results using similitude laboratory experiments.
Dr. Sahu is currently working as a Postdoctoral Research Associate at the University of Cambridge with Dr. Jerome Neufeld in the BP Institute for Multiphase Flow (Dec. 2017-Jun. 2020), where he is investigating the effects of mixing due to dispersion in gravity currents in porous media in the context of Carbon Capture and Sequestration (CCS). Before moving to Cambridge, he pursued PhD in Mechanical Engineering under the guidance of Dr. Morris Flynn at the University of Alberta,Canada (Aug. 2012-Aug. 2016). Prior to starting his PhD, he worked in General Electric Co. (GE) for a year. Before then, he pursued Master of Engineering from the Indian Institute of Science, Bangalore and undergraduate degree from Bhilai Institute of Technology, Durg, Chhattisgarh, both in Mechanical Engineering.