Sig Turbulence/Library Added Incompressible RAS Models/kOmegaSSTF
Contents
1 kOmegaSSTF incompressible RAS model
The kOmegaSSTF model was developed by:
Gyllenram, W. and Nilsson, H., Design and Validation of a Scale-Adaptive Filtering Technique for LRN Turbulence Modeling of Unsteady Flow, JFE, May 2008, Vol.130.
It sets an upper limit ( or lt below) to the modelled length scale (
or Lt below), applied to
:
where
.
should be greater than 1. The value 3 was determined in Gyllenram and Nilssson, Very Large Eddy Simulation of Draft Tube Flow, IAHR Symposium, Yokohama, 2006.
and
are the discetized time and length scales.
The filter is applied to the turbulent viscosity:
where is the length scale given by the turbulence model.
The implementation of the kOmegaSSTF model is the same as that for the kOmegaSST model, except for the following difference:
kOmegaSST:
// Re-calculate viscosity nut_ = a1_*k_/max(a1_*omega_, F2()*sqrt(S2));
kOmegaSSTF: (please help me implement this more general!)
// Compute Filter scalar alph = 3.0; //Should be in a dictionary scalarField Lt = sqrt(k_)/(betaStar_*omega_); scalarField lt = alph*Foam::max(Foam::pow(mesh_.V().field(), 1.0/3.0), (mag(U_)*runTime_.deltaT())->internalField()); // Re-calculate viscosity nut_.internalField() = Foam::min(Foam::pow(lt/Lt,4.0/3.0), 1.0)* (a1_*k_/max(a1_*omega_, F2()*sqrt(S2)))->internalField();
1.1 Usage
Modify the RASModel in constant/RASproperties to:
RASModel kOmegaSSTF;
and add to the same file:
kOmegaSSTFCoeffs { alphaK1 0.85034; alphaK2 1.0; alphaOmega1 0.5; alphaOmega2 0.85616; gamma1 0.5532; gamma2 0.4403; beta1 0.0750; beta2 0.0828; betaStar 0.09; a1 0.31; c1 10; Cmu 0.09; }
Make sure that the addedIncormpressibleRASModels library is linked to by adding at the end of the system/controlDict file:
libs ("libaddedIncompressibleRASModels.so");
1.2 Current limitations
- None :-)
- Note that this is a model for unsteady simulations. Steady simulations will most likely not converge to a steady solution.
1.3 Tutorial
In the kOmegaSSTF directory there is a pitzDaily tutorial
Run:
cd $WM_PROJECT_USER_DIR/src/turbulenceModels/RAS/incompressible/kOmegaSSTF/tutorials/pitzDaily blockMesh turbFoam >& log
One of the Dellenback Abrupt Expansion case-study cases also uses kOmegaSSTF by default.
1.4 Utility writekOmegaSSTFilter
In the kOmegaSSTF directory there is a utility named writekOmegaSSTFilter, which is used to write out the filter function, , for viewing in paraFoam or other manipulation.
Compile:
cd $WM_PROJECT_USER_DIR/src/turbulenceModels/RAS/incompressible/kOmegaSSTF/utilities/writekOmegaSSTFilter/ wmake
Run:
writekOmegaSSTFilter
2 Others
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