Large-Eddy Simulation of Flow over Two-Dimensional Obstacles: High Drag States and Mixing

Abstract

Abstract A three-dimensional large-eddy simulation (LES) model was used to examine how stratified flow interacts with bottom obstacles in the coastal ocean. Bottom terrain representing a 2D ridge was modeled using a finite-volume approach with ridge height (4.5 m) and width (∼30 m) and water depth (∼45 m) appropriate for coastal regions. Temperature and salinity profiles representative of coastal conditions giving constant buoyancy frequency were applied with flow velocities between 0.16 and 0.4 m s−1. Simulations using a free-slip lower boundary yielded flow responses ranging from transition flows with relatively high internal wave pressure drag to supercritical flow with relatively small internal wave drag. Cases with high wave drag exhibited strong lee-wave systems with wavelength of ∼100 m and regions of turbulent overturning. Application of bottom drag caused a 5–10-m-thick bottom boundary layer to form, which greatly reduced the strength of lee-wave systems in the transition cases. A final simulatio...