Graduation Year
2013
Document Type
Dissertation
Degree
Ph.D.
Degree Granting Department
Civil and Environmental Engineering
Major Professor
Andrés E. Tejada-Martínez
Keywords
KPP, Numerical simulation, RANS Parametrization, Stokes Drift velocity, Tidal Channel, Turbulent Channel
Abstract
Langmuir turbulence in the upper ocean is generated by the interaction between the wind-driven shear current and the Stokes drift velocity induced by surface gravity waves. In homogenous (neutrally stratified) shallow water, the largest scales of Langmuir turbulence are characterized by full-depth Langmuir circulation (LC). LC consists of parallel counter-rotating vortices aligned roughly in the direction of the wind. In shallow coastal shelves, LC has been observed engulfing the entire water column, interacting with the boundary layer and serving as an important mechanism for sediment re-suspension.
In this research, large-eddy simulations (LES) of Langmuir turbulence with full-depth LC in a wind-driven shear current have revealed deviations from classical log-layer dynamics in the surface and bottom of the water column. For example, mixing due to full-depth LC induces a large wake region eroding the classical bottom (bed) log-law velocity profile. Meanwhile, near the surface, Stokes drift shear serves to intensify small scale eddies leading to enhanced mixing and disruption of the surface velocity log-law.
The modified surface and bottom log-layer dynamics induced by Langmuir turbulence and full-depth LC have important implications on Reynolds-averaged Navier-Stokes simulations (RANSS) of the general coastal ocean circulation. Turbulence models in RANSS are typically calibrated under the assumption of log-layer dynamics, which could potentially be invalid during occurrence of Langmuir turbulence and associated full-depth LC. A K-Profile Parameterization (KPP) of the Reynolds shear stress in RANSS is introduced capturing the basic mechanisms by which shallow water Langmuir turbulence and full-depth LC impact the mean flow. Single water column RANS simulations with the new parameterization are presented showing good agreement with LES
Scholar Commons Citation
Sinha, Nityanand, "Towards RANS Parameterization of Vertical Mixing by Langmuir Turbulence in Shallow Coastal Shelves" (2013). USF Tampa Graduate Theses and Dissertations.
https://digitalcommons.usf.edu/etd/4945
