In past simulations of free-surface waves (both breaking and non-breaking) using RANS models, there have been a marked a collective tendency to over-estimate the turbulence levels. In cases involving breaking waves, this has even been most pronounced prior to breaking with turbulence levels pre-breaking of same order of magnitude as in the surf-zone. The underlying cause was originally identified by Mayer and Madsen (2000) who showed that turbulence production exists in potential flow waves. They further showed that if omega falls below a certain threshold, the model becomes unstable, leading to an exponential growth in both the eddy viscosity and turbulent kinetic energy.
In Larsen and Fuhrman (2018) it was proved that (1) standard two-equation closures (k-omega and k-epsilon) are unconditionally unstable and (2) they can be simply and elegantly stabilized, thus solving this long-standing wide-spread problem.
This repository contains formally stabilized versions of standard two-equation turbulence models for OpenFOAM-v1712 Additonally all versions in this repository, similar to the model in Larsen and Furhman (2018) also include a buoyancy production term. See e.g. Umlauf et al. (2003) or Burchard (2002) for more details.
For any usage of these models please refer to
@article{LarsenFuhrman2018,
title = {On the over-production of turbulence
beneath surface waves in {Reynolds-averaged Navier-Stokes} models},
language = {eng},
author = {Larsen, B. E. and Fuhrman, D. R.},
journal = {J. Fluid Mech.},
VOLUME={853},
pages = {419--460},
year = {2018},
doi = {10.1017/jfm.2018.577},
url= {https://doi.org/10.1017/jfm.2018.577}
}
We acknowledge financial support from the Independent Research Fund Denmark project SWASH: Simulating WAve Surf-zone Hydrodynamics and sea bed morphology, Grant no. 8022-00137B.
Source OpenFOAM-v1712:
source /home/$USER/OpenFOAM/OpenFOAM-v1712/etc/bashrc
In a linux terminal download the package with git by typing:
git clone https://github.com/BjarkeEltardLarsen/stabRAS_v1712.git
Create folder for turbulence model (if the folders already exist skip this part)
mkdir $WM_PROJECT_USER_DIR $WM_PROJECT_USER_DIR/src $WM_PROJECT_USER_DIR/src/TurbulenceModels $WM_PROJECT_USER_DIR/src/TurbulenceModels/turbulenceModels
Move the folder to the user source code
mv stabRAS_v1712 $WM_PROJECT_USER_DIR/src/TurbulenceModels/turbulenceModels/
Go to the directory and compile the turbulence models
cd $WM_PROJECT_USER_DIR/src/TurbulenceModels/turbulenceModels/stabRAS_v1712
wmake libso
Move the tutorials to the desired folder e.g FOAM_RUN
mv Tutorials $FOAM_RUN
The tutorials consist of eight different version of the compiled turbulence models. In each of these tutorials a wave is inialized in a domain which is exactly one wave length long with cyclic boundaries and a slip condition at the bed. This in other words an idealized case where the flow can considered very close to potential flow.
The cases ending with "Stab" have lambda2=0.05 and are stabilized version of the new turbulence models. In these cases the initial turbulence levels will decay in time.
Cases not ending with Stab corresponds to the standard models (with buoyancy production included) and here growth rather than decay in the turbulence level can be seen.
To run a tutorial go to the folder of the tutorials and choose one of the eight cases.
Make the RunScrip excecutable by
chmod +x RunScript
Then run the RunScript by typing (the tutorials will take a few ours depending on speed of the machine)
RunScript
The tutorials folder also contain a small animation, which shows the development in the turbulent kinetic energy for all eight tutorials.
Include the libary of the stabilized turbulence models in the system/controlDict folder
libs
(
"libstabRASModels.so"
);
Change the constant/turbulence Each of the four models can be chosen by uncommenting the desired model. If lambda2=0 the models default to their standard OpenFOAM implementation (but with the buoyancy production term added).
simulationType RAS;
RAS
{
RASModel kOmegaStab;
//RASModel kOmegaSSTStab;
//RASModel kEpsilonStab;
//RASModel RNGkEpsilonStab;
turbulence on;
printCoeffs on;
kOmegaStabCoeffs
{
lambda2 0.05;
}
kOmegaSSTStabCoeffs
{
lambda2 0.05;
}
kEpsilonStabCoeffs
{
lambda2 0.05;
}
RNGkEpsilonStabCoeffs
{
lambda2 0.05;
}
Burchard, H. Applied Turbulence modelling for Marine Waters Springer 2002
Larsen, B.E. and Fuhrman, D.R. On the over-production of turbulence beneath surface waves in RANS models J. Fluid Mech. 853. pp 419-460. https://doi.org/10.1017/jfm.2018.577 2018
Mayer, S. & Madsen, P.A. Simulation of breaking waves in the surf zone using a Navier-Stokes solver. In: Proc. 25th. ICCE, Sydney. Australia, pp. 928-941. 2000
Umlauf, L., Burchard, H. and Hutter, K. Extending the k-omega turbulence model towards oceanic applications Ocean Modelling. 5(3), 195-218 2003