Les and sigma-coordinate rans simulations of laboratory surface wave breaking

This dissertation presents a three-dimensional (3-D) numerical study of the turbulent bubbly flow in surface breaking waves, from steepness-limited unsteady breaking in deep water to depth-limited breaking in the surf zone. Because of available computational resources, the whole range of the relevant scales cannot be resolved in a single high-resolution framework. Instead, two different frameworks are chosen to study the relevant physics from small scales through field scales. In the first framework, a Volume-of-Fluid based Eulerian-Eulerian polydisperse two-fluid model (Ma et al. 2011, Derakhti & Kirby 2014) is used to study breaking-induced energy dissipation, bubble entrainment and liquid-bubble interaction in unsteady whitecaps as well as large-scale turbulent coherent structures and their interaction with dispersed bubbles in the surf zone. A 3-D non-hydrostatic wave-resolving sigma-coordinate framework is chosen as the lower-resolution framework. We derive a new set of equations, in conservative form, describing the kinematics and dynamics of continuous and dispersed phases in a multiphase mixture in a surface- and terrain-following sigma-coordinate system, together with exact surface and bottom boundary conditions for the velocity and dynamic pressure fields as well as a Neumann-type boundary condition for scalar fluxes. The model capability and accuracy to reproduce the evolution of the free surface, velocity and vorticity fields and breaking-induced dissipation in regular and irregular breaking waves from the surf zone to deep water is examined in detail.