Intermittent Wave Breaking-induced Turbulence: a Synergy between High-fidelity Numerical Modeling and Field Observations

Morteza Derakhti, Applied Physics Laboratory University of Washington, Seattle, WA, United States, James M Thomson, Applied Physics Lab (UW), Seattle, WA, United States and James T Kirby Jr, University of Delaware, Civil and Environmental Engineering, Newark, DE, United States
Abstract:
Combining high-fidelity numerical modeling and field observations, we examine the characteristics of intermittent wave breaking-induced turbulence in intermediate and deep water during moderate to high sea states. We use a LES/VOF Eulerian-Eulerian polydisperse two-fluid model (Derakhti & Kirby, 2014, 2016) to simulate bubble entrainment and turbulent bubbly flow in short-crested wave breaking events. Bubble contributions to dissipation and momentum transfer between the water and air phases are considered. Field observations include wave breaking and turbulence measurements by surface following drifters (SWIFTs) obtained in the North Pacific Ocean (Schwendeman and Thomson 2015, Thomson et al, 2016). New observations of wave breaking and turbulence during high sea states are planned (Dec. 2019) and will be also presented.

In particular, we examine the spatial distribution of turbulent dissipation rates inside and outside of the bubble plumes associated with each breaking event. In addition, we reconcile the field measurements of SWIFTs with our numerical model results. Conversion of the model results to a surface-following reference frame, along with scaling of the model domain to match observations of whitecap coverage, are essential steps. We show that convergence of statistics occurs after approximately 1000-3000 randomly spaced observations in time and space relative to 3D breaking events. We further show important effects of obscuration of velocity measurements due to entrained bubbles on the estimated turbulent dissipation rates. Finally, we examine recent formulations that relate wave dissipation rates to the volume and kinematics of each bubble plume.