Slip vs. Symmetry boundary condition

Madeleine P. Vincent · March 6, 2015, 14:57

Hi all,

I am interested in the difference in OpenFOAM between a slip and a symmetry boundary condition for simpleFoam and pisoFoam, version 2.2.

Specifically, this is for a far field edge that should see flow almost entirely parallel to the wall. In this case I am looking at steady, incompressible flow, though later I will be looking at unsteady.

Does OpenFOAM calculate the two boundary conditions differently?

In this post:

http://www.cfd-online.com/Forums/ope...condition.html

it says that they are treated identically (except for perhaps pre- and post-processing).

However, when I switch my far-field BC's to slip from symmetry, the results are slightly different (in this case using simpleFoam). Thus I don't agree with the statements made in the post above.

[Perhaps OF has changed since that post was made, which would be an explanation.]

Does anyone have a good explanation?

Thanks,
Madeleine.

Andela · December 20, 2016, 08:38

Dear all,

I am also interested in answer, so if anybody can explain it it would be nice.

Regards

alexeym · December 20, 2016, 12:07

Hi,

Just take a look at two files:

1. $FOAM_SRC/finiteVolume/fields/fvPatchFields/basic/basicSymmetry/basicSymmetryFvPatchField.H
2. $FOAM_SRC/finiteVolume/fields/fvPatchFields/derived/slip/slipFvPatchField.H

slip is a child of basicSymmetry.

"the results are slightly different" from the post you are reviving means nothing without concrete numbers and figures.

March 6, 2015, 14:57	Slip vs. Symmetry boundary condition	#1
Madeleine P. Vincent New Member Madeleine P. Vincent Join Date: May 2011 Posts: 29 Rep Power: 15	Hi all, I am interested in the difference in OpenFOAM between a slip and a symmetry boundary condition for simpleFoam and pisoFoam, version 2.2. Specifically, this is for a far field edge that should see flow almost entirely parallel to the wall. In this case I am looking at steady, incompressible flow, though later I will be looking at unsteady. Does OpenFOAM calculate the two boundary conditions differently? In this post: http://www.cfd-online.com/Forums/ope...condition.html it says that they are treated identically (except for perhaps pre- and post-processing). However, when I switch my far-field BC's to slip from symmetry, the results are slightly different (in this case using simpleFoam). Thus I don't agree with the statements made in the post above. [Perhaps OF has changed since that post was made, which would be an explanation.] Does anyone have a good explanation? Thanks, Madeleine.

December 20, 2016, 08:38		#2
Andela New Member Marija Bervida Join Date: Mar 2016 Location: Slovenia Posts: 9 Rep Power: 10	Dear all, I am also interested in answer, so if anybody can explain it it would be nice. Regards __________________ Things are not what they seem; nor are they otherwise.

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December 20, 2016, 12:07		#3
alexeym Senior Member Alexey Matveichev Join Date: Aug 2011 Location: Nancy, France Posts: 1,938 Rep Power: 39	Hi, Just take a look at two files: 1. $FOAM_SRC/finiteVolume/fields/fvPatchFields/basic/basicSymmetry/basicSymmetryFvPatchField.H 2. $FOAM_SRC/finiteVolume/fields/fvPatchFields/derived/slip/slipFvPatchField.H slip is a child of basicSymmetry. "the results are slightly different" from the post you are reviving means nothing without concrete numbers and figures.