A NEW VIEW OF TURBULENT FLOW OVER SOLUBLE BEDROCK FORMS

When investigating flow over soluble bedrock, numerical models are frequently used to illuminate the role of driving geomorphological processes, including dissolution, mechanical erosion, and the transport of solutes, and sediment. The role and interactions of which are not yet fully understood. The morphogenesis of scallops is an outstanding puzzle as current chemical theory prohibits the variability in dissolution rate necessary for scallops to develop. Most numerical models used to study these processes utilize simplifying assumptions in order to ensure tractability. This means that the fine scale behaviors associated with the driving processes are not modeled. While Computational Fluid Dynamics (CFD) enables relaxation of these assumptions, the majority of CFD studies use simplifying design decisions to avoid the computational cost of directly modeling turbulence. These decisions often mean that the effects of sub-grid scale turbulence are ignored for the sake of computational speed. Within soluble bedrock systems, the evolution of morphologies on the reach-scale and smaller can be driven by contrasts in dissolution rate and the distribution of turbulent effects over such scales.

To improve our understanding of the role of turbulence in the development of morphologies in soluble bedrock systems, such as scallops and flutes, we incorporate Large-Eddy Simulation (LES) into our CFD models using the lattice-Boltzmann method. By using LES, sub-grid scale turbulent effects are modeled and incorporated into the flow dynamics. By resolving these effects, our models have produced turbulent structures that have heretofore not been present in studies of flow over scallops and flutes using CFD models. These turbulent structures can enhance the transport of solute away from the fluid-solid interface, which can increase the dissolution rate. This represents a partial means for resolving the conundrum surrounding scallop morphogenesis.