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May 17, 2005, 10:04 
What is the difference? If I m

#1 
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Luckyluke
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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 
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Luckyluke
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Who give me a few words? ^_^


May 19, 2005, 10:14 
zeroGradient sets the boundary

#3 
Senior Member
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zeroGradient sets the boundary value to the nearwall cell value whereas a symmetryPlane is a symmetryplane which is the same thing for scalars but not for vectors or tensors.


January 15, 2012, 03:06 
Desciption / maths of symmetryPlane boundary condition

#4  
New Member
Join Date: Mar 2011
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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:
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 
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Brendan
Join Date: Dec 2011
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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

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, 23:22 

#7 
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Ali Q Raeini
Join Date: Feb 2010
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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. 

December 8, 2012, 09:51 

#8 
Member

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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