# Boundary conditions symmetryPlane vs zeroGradient

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 May 17, 2005, 10:04 What is the difference? If I m #1 Member   Luckyluke Join Date: Mar 2009 Posts: 51 Rep Power: 17 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.

 May 19, 2005, 10:10 Who give me a few words? ^_^ #2 Member   Luckyluke Join Date: Mar 2009 Posts: 51 Rep Power: 17 Who give me a few words? ^_^

 May 19, 2005, 10:14 zeroGradient sets the boundary #3 Senior Member   Join Date: Mar 2009 Posts: 854 Rep Power: 22 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.

January 15, 2012, 02:06
Desciption / maths of symmetryPlane boundary condition
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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 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

 April 16, 2012, 13:01 #5 New Member   Brendan Join Date: Dec 2011 Posts: 7 Rep Power: 14 I would also like to know the difference if there is anyone out there with an idea? Thanks

 April 23, 2012, 03:18 SymmetryPlane facts #6 Member   Mohammad Fereshtehpour Join Date: Jul 2011 Location: Iran Posts: 61 Rep Power: 14 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?

 December 7, 2012, 22:22 #7 New Member   Ali Q Raeini Join Date: Feb 2010 Posts: 24 Rep Power: 16 too late but, I had a quick look, apparently the boundary field is assigned in function: Foam::basicSymmetryFvPatchField::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.

 December 8, 2012, 08:51 #8 Member   Duong A. Hoang Join Date: Apr 2009 Location: Delft, Netherlands Posts: 93 Rep Power: 17 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 fumiya, vigneshTG, vishnu_240 and 12 others like this.

February 11, 2017, 09:12
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samane dortaj
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Quote:
 Originally Posted by henry 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.
Hi,
in tutorials,lagrangian,DPMFoam,goldschmidt, this BC is used for p and u, so we can use it for vectors.