The turbulent dynamics of quasi-steady spilling breakers: Theory and experiments

This dissertation provides a detailed description of the turbulence structure and its effects on the mean flow of fully-formed quasi-steady spilling breakers. Laboratory experiments are conducted for an air-entraining turbulent hydraulic jump in Froude similitude with saturated surf-zone breakers. Particle image velocimetry measurements are used to investigate the mean and turbulent structure of the flow, with particular attention to the surface intermittency. The streamwise variation of the turbulent length scales and growth rates in the breaker shear layer are in good agreement with values found in mixing layers. The combined effects of flow-deceleration and adverse pressure gradient upstream of the foot of the breaker are responsible for the separation of the shear layer causing breaking. A theoretical model is developed for the evolution of the turbulent dynamics in a spilling breaking wave. The theoretical model provides an accurate mathematical incorporation of the effects of the two-phase surface layer, unsteadiness, curvature, rotation, and non-hydrostatic effects. Evolution equations are derived for the mean flow and turbulent kinetic energy in the breaker shear layer. Several physical mechanisms of the flow in different regimes are studied through geometric and kinematic scaling assumptions and comparisons made with experimental observations. The governing equations are then integrated across the shear layer to develop boundary conditions for the irrotational flow underneath. Coherent turbulent structures are analyzed through kinematic and statistical techniques applied to the experimental data. The sizes and topologies of these structures provide valuable insights into the dominant modes of turbulence in the breaker shear layer.