CMS-Flow:Subgrid Turbulence Model
In CMS-Flow eddy viscosity is calculated as the sum of a base value , the current-related eddy viscosity and the wave-related eddy viscosity
The base value for the eddy viscosity is approximately equal to the kinematic eddy viscosity can be changed using the advanced cards (Click [here] for further details).
Current-Related Eddy Viscosity Component
There are four options for the current-related eddy viscosity: FALCONER, PARABOLIC, SUBGRID, and MIXING-LENGTH. The default turbulence model is the subgrid model, but may be changed with the advanced card TURBULENCE_MODEL.
The Falconer (1980) equation is the method is the default method used in the previous version of CMS, known as M2D. The first is the Falconer (1980) equation given by
where is the bottom friction coefficient, is the depth-averaged current velocity, and is the total water depth.
The second option is the parabolic model given by
where is approximately equal to .
Subgrid Turbulence Model
The third option for calculating is the subgrid turbulence model given by
where and are empirical coefficients related the turbulence produced by the bed and horizontal velocity gradients, and is the average grid area. is approximately equal to 0.0667 (default) but may vary from 0.01-0.2. is equal to approximately the square of the Smagorinsky coefficient and may vary from 0.1 to 0.5 (default is 0.4). is equal to
The subgrid turbulence model parameters may be changed in the advanced cards EDDY_VISCOSITY_BOTTOM, and EDDY_VISCOSITY_HORIZONTAL.
Mixing Length Model
Wave-Related Eddy Viscosity
The wave component of the eddy viscosity is calculated as
where is an empirical coefficient with a default value of 0.5 but may vary between 0.25 and 1.0. is the significant wave height and is bottom orbital velocity based on the significant wave height. may be changed using the advanced card EDDY_VISCOSITY_WAVE.
Outside of the surf zone the bottom orbital velocity is calculated as
where is the significant wave height, is the peak wave period, is the wave number. Inside the surf zone, the turbulence due to wave breaking is considered by increasing the bottom orbital velocity as
- LARSON, M.; HANSON, H., and KRAUS, N. C., 2003. Numerical modeling of beach topography change. Advances in Coastal Modeling, V.C. Lakhan (eds.), Elsevier Oceanography Series, 67, Amsterdam, The Netherlands, 337-365.