standard kEpsilon, kqRWallFunction and epsilonWallFunction (why should give value ?)
Dear foamers:
I have been confused by the k and epsilon wall boundary condition in tutorials/imcompressible/simpleFoam/pitzDaily/0. It write like this: upperWall { type kqRWallFunction; value uniform 0.375; } upperWall { type epsilonWallFunction; value uniform 14.855; } in general, standard k-epsilon model, in the wall using wall function, that means k can be got by solving k equation(using dk/dn=0 in the wall), then epsilon or velocity can be got through empirical formular. But I don't understand the exact meaning of kqRWallFunction and epsilonWallFunction, why should give a value here. I want to know it is neglected automaticly when using kEpsilon model. Or if I use zeroGradient for k and epsilon in the wall will be better ? Thanks for your reply. |
I have try, if use zeroGradient for k and epsilon in the wall, the result a little not good. why ?
I remember that in OpenFOAM-1.5 , just use zeroGradient for k and epsilon in the wall. kqRWallFunction and epsilonWallFunction just begin to use in 1.6 version. I am confused. If OpenFOAM use standard wall function for kEpsilon model ? |
Take a look at the file in your OpenFOAM dictionary:
OpenFOAM-1.6/src/turbulenceModels/incompressible/RAS/RASModel/RASModel.C at line 148. Maby it can help you. |
input kqRWallFuntion meaning
Hi,
Can you please explane me the meaning of the input I have to give to (for exemple turbulent kinetic energy) near walls: { type kqRWallFunction; value uniform 0.001; } how to use k-epsilon without wall function (corresponding to Enhanced wall treatment in fluent)? thanks |
kqRWall Functions
Hello Panda,
I am trying to use the same wall function but I am not able to understand what it stands for. Did you figure out the answer to the question you asked here? My function is defined as below. { type kqRWallFunction; value uniform 0.375; } } This is similar to Omega, { type omegaWallFunction; Cmu 0.09; kappa 0.41; E 9.8; beta1 0.075; value uniform 3.5; } Where do I find all these coefficients? How does changing them has an impact on the overall solution. I looked at the file name given above, but I didn't get it. Thanks, Subhkirti. |
Try Doxygen
You can search Doxygen to find where functions are defined. Here's the Doxygen definition of kqRWallFunction from Doxygen:
Detailed Description template<class Type> class Foam::incompressible::RASModels::kqRWallFunctionFv PatDetailed Description template<class Type> class Foam::incompressible::RASModels::kqRWallFunctionFv PatchField< Type > Boundary condition for turbulence k, Q, and R when using wall functions. Simply acts as a zero gradient condition. Source files kqRWallFunctionFvPatchField.H kqRWallFunctionFvPatchField.C Definition at line 50 of file kqRWallFunctionFvPatchField.H. chField< Type > Boundary condition for turbulence k, Q, and R when using wall functions. Simply acts as a zero gradient condition. Source files kqRWallFunctionFvPatchField.H kqRWallFunctionFvPatchField.C Definition at line 50 of file kqRWallFunctionFvPatchField.H. Turbulence model standard coefficients are defined in source code. For example, look in /src/turbulenceModels/incompressible/RAS/kEpsilon/kEpsilon.C. If you want to change the coefficients, it's easy to do in the RASProperties file in /constant directory of your simulation. To modify K-Epsilon coefficients, insert the following lines after turbulence on: kEpsilonCoeffs { Cmu x.x; C1 y.y; C2 z.z; } This will change the three listed coefficient values and leave the default values for the others. Alan |
meaning of the value of kqRWallFunction
Hello,
Can anybody explain me which is the meaning of the "value uniform" one sets on the wallFunction for k? wall { type kqRWallFunction; value uniform 0.00735; } Thank you for your help! |
Hi Jose,
I had the same question and got an answer here: http://www.cfd-online.com/Forums/ope...lon-omega.html The value specified with a wall function is kind of an initial guess. Greetings Gerard P.S.: Sorry for the misspelling of you name, I am not used to the keys I use at this moment. |
kqRWallFunction
Hi Foamers,
I have a question about the standard wall function. I read that at high Reynolds number in the closest cell to the wall we should calculate the k by this equation: k= sqr (utau)/Cmu25 but I have seen that everywhere it is recommended to use kqRWallFunction that in fact gives the zeroGradient boundary condition. Could anybody help me to understand this? Regards, Amir |
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