USING COMPUTATIONAL FLUID DYNAMICS TO MODEL THE FLUID-SOLID INTERFACE IN KARST CONDUIT SYSTEMS

Numerical models are frequently used to investigate the processes occurring in karst systems, including dissolution and the transport of solute, sediment and contaminants. However, the role and interactions between driving processes occurring in karst aquifers are not yet fully understood. Numerical models used to study these processes typically utilize simplifying assumptions in order to ensure tractability. Most notably, within numerical models of speleogenesis, the treatment of dissolution using fracture or pipe flow equations, with an assumed uniform rate within each segment of the network, means that the fine scale behaviors associated with dissolution at the fluid-solid (F-S) interface are not modeled. Within natural caves the evolution of morphologies on the reach-scale and smaller can be driven by contrasts in dissolution rates over such scales. Within most speleogenesis models, this variability in dissolution rate at small scales does not occur, and the resulting detailed morphological features cannot manifest along the conduits. Models that do attempt to simulate dissolution processes along the F-S interface have not yet been developed to a point where the spatial and temporal resolutions are sufficient to capture the desired behavior.

Through the use of computational fluid dynamics, the processes occurring at the F-S interface can be modeled on a finer scale than in almost all existing studies. Resolving fine scale behavior at the F-S interface, such as the diffusive boundary layer, is particularly important when examining the small scale structures that result from complex F-S interactions that evolve over time. This is an important consideration in karst systems, where surface features, such as scallops, develop over the course of system maturation. Though many such morphologies are used in the interpretation of past processes of speleogenesis, a quantitative understanding of their formation and evolution remains elusive.