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-   -   question on nonuniform BC (http://www.cfd-online.com/Forums/openfoam-pre-processing/67213-question-nonuniform-bc.html)

grig August 7, 2009 05:58

question on nonuniform BC
 
Hi, I have a question about setting up nonuniform BC's in OF. Namely, when specifying the whole list of values, are these numbers assigned to the points in the center of each boundary cell face or are these values assigned for the whole boundary cell face? Thanks:)

grig August 11, 2009 04:06

Does anyone have an idea? I am new to OF and this would really help... I would also ask if blockMesh can be used to create unstructured grids? Sorry if the questions seem lame. Thanks!

henrik August 11, 2009 04:53

Dear Grig,

1) Yes, blockMesh can be used to create unstructured grids using the the mergePatchPairs keyword. You can find an example in

$FOAM_TUT/simpleFoam/pitzDaily3Block/constant/polyMesh/blockMeshDict

But I am not sure whether this is what you are after.

2) Yes, the values are assigned at the face centers and in order of the face list. If you have a function that describes your boundary, you either write your own BC or use "groovyBC":

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

If you have the values at some arbitrary points, you may want to use "timeVaryingMappedFixedValue" used here:

$FOAM_TUT/simpleFoam/pitzDailyExptInlet

Henrik

grig August 11, 2009 05:00

Thank you very much for the reply. So, if the values are assigned for the face center, than are they also interpolated over the whole boundary cell face during solving?! I am asking this because I want to implement a certain velocity value in a particular boundary cell and it seems to me that the values shown in paraFoam are 4 times lower all the time?!
I will have a look at the mergePatchPairs example.

Thank you again!

henrik August 11, 2009 05:13

Dear Grig,

with cell and faces your are at the atomic level of the finite volume method which assumes that that face and cell values are uniform.

Henrik

grig August 11, 2009 05:19

Ok, then there must be some other problem because, talking specifically, I assigned to only one boundary (wall) cell a velocity of 10 m/s, but when I visualize in paraFoam it shows around 2.5. This why I am a bit puzzled...

Best,
Grig

henrik August 11, 2009 08:39

Dear Grig,

make sure that you plot the cell values. That's the fat icon rather than the pointy one in paraview's field selector. Each cell/face should then get a unique color - no shading.

Alternatively, have a look into the output files to work out what the exact value is.

Henrik

grig August 11, 2009 09:07

Thanks, I will have a look. Best, Grig.

tamsilian May 26, 2010 11:56

help about groovyBC
 
Hi sir/madam
i simulated polymer in extruder(screw mill) by ViscoElastic fluidFoam,Jovani. According to my geometry, velocity vectors in boundary condition are changed .As result i should code variables condition in 0File>> U>> movingWalls.do you know that GroovyBC was compiled to OpenFoam as defualt or i have to compile it?and how to compile groovyBC to OpenFoam v.1.6?if anybody coded one geometry by groovyBC this is thanksful to sent it me by tamsilian@gmail.com.
Thanks in advanced your help


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