LES and σ-coordinate RANS simulations of laboratory surface wave breaking

Kirby, James T.This dissertation presents a three-dimensional (3D) 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 can not 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 (VOF) based Eulerian-Eulerian polydisperse two- fluid model (Ma et al. 2011, Derakhti & Kirby 2014b) is used to study breaking-induced energy dissipation (chapter 2), bubble entrainment and liquid-bubble interaction (Derakhti & Kirby 2014b) in unsteady whitecaps as well as large-scale turbulent coherent structures and their interaction with dispersed bubbles in the surf zone (chapter 3). A 3D nonhydrostatic wave-resolving -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 -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 (chapter 4). The model capability and accuracy to reproduce the evolution of the free surface, velocity and vorticity fields and breaking-induced dissipation under regular and irregular breaking waves from surf zone to deep water is examined in detail (chapter 5).University of Delaware, Department of Civil and Environmental EngineeringPh.D