Objectives: The objective of the proposed research is to determine the length and time scales of evolving high Rayleigh number (Ra) thermal convection in subsurface porous media. The specific hypothesis that will be tested is that flow patterns have several interacting scales of motion occurring simultaneously that influence each other. The smallest scales are individual plumes that peel away from a thermal boundary layer, while the largest scales are on the order of the size of the experimental apparatus. The length and time scales of motion, as well as temporal heat transfer can be understood in terms of the local (boundary layer) and global (system) Rayleigh numbers, the Nusselt number, the Peclet number, as well as the heterogeneity of the media. Scientific merit: Thermal convection is an important transport process that can result in high heat flow rates in regions of the Earth's crust. While much focus in porous media has been on the closed convection cells that result in confined media at low Rayleigh numbers, little research, and no fundamental experiments, have been conducted in parameter space where the cells themselves become unstable and transition to a turbulent regime. Methods: A series of experiments will be conducted in a sand-filled laboratory test cell with dimensions 1 m tall x 1 m wide x 2 cm thick. Bedding patterns will be constructed using translucent silica sands of varying sizes (100 ?m to 7 mm). An array of approximately 75 thermocouples will be installed around the center of the cell to capture cm-scale temperature (hence flow) motion. Large-scale motion will be visualized by dissolving thermochromic liquid crystals in the working solution (water); these crystals change color (red-green-blue) as a function of temperature.
Broader impacts: This research will form the dissertation portion of a Ph.D. student's curricula at the University of Nevada, Reno. This research is part of a larger goal of C. Cooper to develop methods to understand the importance of subsurface fluid mechanics as a geologic agent.
