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-   -   Boundary conditions symmetryPlane vs zeroGradient (http://www.cfd-online.com/Forums/openfoam-solving/60595-boundary-conditions-symmetryplane-vs-zerogradient.html)

luckyluke May 17, 2005 10:04

What is the difference? If I m
 
What is the difference? If I model the RT instability in a box, what conditions should be set to left,right,top and bottom boundaries for gamma?

Thanks.

luckyluke May 19, 2005 10:10

Who give me a few words? ^_^
 
Who give me a few words? ^_^

henry May 19, 2005 10:14

zeroGradient sets the boundary
 
zeroGradient sets the boundary value to the near-wall cell value whereas a symmetryPlane is a symmetry-plane which is the same thing for scalars but not for vectors or tensors.

RygeltheXVI January 15, 2012 03:06

Desciption / maths of symmetryPlane boundary condition
 
Hail,

I'm trying to work out description of what he symmetryPlane boundary condition actually is. I haven't had any luck with either the user nor programmers guide.

This thread gives the most mathematical description that I can find online but is still incomplete:
Quote:

Originally Posted by henry (Post 194427)
zeroGradient sets the boundary value to the near-wall cell value whereas a symmetryPlane is a symmetry-plane which is the same thing for scalars but not for vectors or tensors.

What is it for vectors? (If it was just normal component zero, then it would be the same as a slip boundary condition).

I have tried but have no luck interpreting the source code: and even then I don't know which one to look at (I don't know which of /src/finiteVolume/fields/fvPatchFields/basic/basicSymmetry or /src/finiteVolume/fields/fvPatchFields/constraint/symmetry [if either, it could be another one] corresponds to symmertyPlane).

If anyone knows which, or preferably a description of what the symmetryPlane boundary condition does, it would be very much appreciated.

Many Thanks
Rygel

guitarbren April 16, 2012 13:01

I would also like to know the difference if there is anyone out there with an idea?
Thanks

MOHAMMAD67 April 23, 2012 03:18

SymmetryPlane facts
 
Dear Foamers
Is there anyone here help us to have more information about that? I obserevd some differences between the results of the model with and without symmetryPlane?

aliqasemi December 7, 2012 23:22

too late but, I had a quick look, apparently the boundary field is assigned in function: Foam::basicSymmetryFvPatchField<Type>::evaluate. It makes use of transform boundary condition, and I didn't decode it thoroughly. However, my speculation is as follows:

For vector fields, the value of the field on the patches with type "symmetryPlane" are calculated by projecting the patchInternalField to the patch. They are calculated as the average of the patchInternalField values and their mirrors in the patch faces.

duongquaphim December 8, 2012 09:51

Hi,

For zeroGradient, both scalar and vector field are set as the value of the cell near the patch by setting surface normal gradient to 0: grad(f) = (f_P - f_N)/delta = 0 (programmerGuide page 40).

With symmetryPlane, for a scalar, the computation is similar to zeroGradient. For a vector, to make it simple, all components parallel to the patch is mirrored while the normal component is set to zero. Looking at the code of OpenFOAM at src/finiteVolume/fields/fvPatchFields/basic/basicSymmetry, I think they use transformation matrix to compute the new value on the BC. The method can be find in http://en.wikipedia.org/wiki/Householder_transformation

Regards,

Duong


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