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How to sample including value of boundary points

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Old   April 14, 2017, 18:29
Default How to sample including value of boundary points
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TML
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Hello,

I am running a 2D annular flow case, and I am trying to get velocity distribution at a certain location using sample utility. The problem is that the result gives by sample does not include the boundary point which should be (0 0 0) for a no-slip wall. I have tried cellPoint, cellPointFace, and cellPatchConstrained for the interpolationScheme, but none of them works.

This is my sampleDict:

FoamFile
{
version 2.0;
format ascii;
class dictionary;
object sampleDict;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

setFormat csv;


interpolationScheme cellPatchConstrained;


fields
(
Ux
);

sets
(
lineX1
{
type uniform;
axis y;

start (0.06 0.02 0); //inner wall
end (0.06 0.03 0); //outer wall
nPoints 40;
}

);
//************************************************** * //

Any help is appreciated!

Last edited by TML; April 17, 2017 at 11:34.
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Old   April 15, 2017, 02:09
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Uwe Pilz
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You let sample calculate the values at a very short perpendicular line which doesn't contain your (0 0 0 ) point.
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Old   April 17, 2017, 11:33
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Quote:
Originally Posted by piu58 View Post
You let sample calculate the values at a very short perpendicular line which doesn't contain your (0 0 0 ) point.
Thanks for the reply.

But my start and end point are on the inner and outer wall of the annular cylinder respectively, which should contain the (0 0 0) velocity.
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Old   April 17, 2017, 14:27
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Please keep in mind: The velocity is modeled, and the last calculated value is the one of the first cell beyond the boundary. Values inside this cell (toward the boundary) are extrapolated.
Beside this it depends form your wall function which velocity you get near the boundary. There is a contradiction between capturing the behavior of the flow very near the boundary and the overall approach of the boundary layer: Both can only covered with DNS.

It may be en-lighting of you look at the velocity at every cell around the cylinder and next the cell toward the flow.
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Die der Hauptbewegung überlagerte Schwankungsbewegung ist in ihren Einzelheiten so hoffnungslos kompliziert, daß ihre theoretische Berechnung aussichtslos erscheint. (Hermann Schlichting, 1950)
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