Farhadzadeh, A. and Gangai, J., 2017. Numerical modeling of coastal storms for ice-free and ice-covered Lake Erie. Lake Erie is the shallowest among the Great Lakes. Because of its shallow depth and because predominant wind direction in the area is along the lake's longitudinal axis, eastern and western Lake Erie experience significant storm surge that are usually followed by seiches. The lake warms in summer and quickly freezes over in winter when it often develops extensive surface ice. The surface ice, in turn, can modify wind setup and waves and even hinder wave propagation in areas where the surface ice is densely concentrated. In the following, a coupled numerical model for storm surge and wave is utilized for the simulation of Lake Erie coastal storms under ice-free and ice-covered lake conditions. Six extreme events, affecting both eastern and western Lake Erie, are selected for presentation here. A high resolution mesh is developed using the National Oceanic and Atmospheric Administratio...

Computational modeling of open-channel flows at low Froude ($\mathsf{F}$ ) numbers is often carried out using the rigid-lid assumption to prescribe the water surface location. However, the presence of wall-mounted hydraulic structures could cause $\mathsf{F}$ to locally exceed unity, inducing a transition from subcritical to supercritical flow, locally accelerate the flow generating high-energy turbulent eddies at a constriction region, and lead to the formation of backwater at upstream regions. Under such circumstances, the rigid-lid assumption may not be adequate to obtain reliable flow field simulations. Previous investigation to examine the effect of a rigid-lid assumption on large-eddy simulation (LES) of a low-Reynolds open-channel flow showed that the second-order turbulent statistics are altered depending on the free-surface resolving method. In this work, we seek to study the rigid-lid effect on high-Reynolds LES applicable to natural river flows. We employed an in-house Virtual Flow Simulator (VFS-Geophysics) model in its LES mode to simulate the flow field in a similar test case that is scaled up to obtain a high Reynolds of $7.9\times {10}^4$ . We performed LES evaluating the two free-surface resolving approaches: rigid-lid and level-set. The flow field and free-surface computations were validated using a series of measured data that we obtained by carrying out laboratory experiments. Our LES results indicate that at near-bed regions of the flume and around the bridge abutment, both the first- and second-order turbulent statistics are influenced by the method selected to prescribe the water surface.

Barchans are an important signature of turbulent atmospheric and aquatic flows on parts of the Earth’s surface where the supply of sediments is scarce. Khosronejad and Sotiropoulos [“On the genesis and evolution of barchan dunes: Morphodynamics,” J. Fluid Mech. 815, 117–148 (2017)] demonstrated that high-fidelity hydro-morphodynamic large-eddy simulation (LES) can replicate sub-aqueous barchan fields exhibiting the geometric features and morphodynamic interactions observed in nature. Herein, we first validate the ability of our LES method to simulate mean flow and turbulence statistics over a frozen barchan dune created in a control laboratory experiment. We then analyze our high-fidelity LES datasets to elucidate the hydrodynamic phenomena that drive the previously identified morphodynamic interactions at various stages of subaqueous barchan dune evolution, from flatbed to quasi-equilibrium. We uncover and quantify the hydrodynamic mechanisms that cause (i) the initiation of crescent microfeatures on the initial flatbed; (ii) the development of three-dimensional barchan dunes; and (iii) several other phenomena that occur during the barchan field maturation, such as the birth of new small barchans and the exposure of the underlying bedrock in the wake of the barchans. Defining a dimensionless timescale, i.e., the saturation timescale, as a function of the saturation length scale, we attempt to categorize for the first time various temporal stages of barchan field development. We show that the barchan field has specific characteristics corresponding to each of the barchan stage developments in terms of both the flow field and the bed topology. Comparing the simulation results of transverse and barchan dunes, we illustrate that the two dune types have similar topographic and hydrodynamics characteristics until bedrock exposure occurs.