# How to sample including value of boundary points

 Register Blogs Members List Search Today's Posts Mark Forums Read

 April 14, 2017, 18:29 How to sample including value of boundary points #1 New Member   TIAN Join Date: Apr 2017 Posts: 2 Rep Power: 0 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.

 April 15, 2017, 02:09 #2 Senior Member     Uwe Pilz Join Date: Feb 2017 Location: Leipzig, Germany Posts: 588 Rep Power: 9 You let sample calculate the values at a very short perpendicular line which doesn't contain your (0 0 0 ) point. __________________ Uwe Pilz -- Die der Hauptbewegung überlagerte Schwankungsbewegung ist in ihren Einzelheiten so hoffnungslos kompliziert, daß ihre theoretische Berechnung aussichtslos erscheint. (Hermann Schlichting, 1950)

April 17, 2017, 11:33
#3
New Member

TIAN
Join Date: Apr 2017
Posts: 2
Rep Power: 0
Quote:
 Originally Posted by piu58 You let sample calculate the values at a very short perpendicular line which doesn't contain your (0 0 0 ) point.

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.

 April 17, 2017, 14:27 #4 Senior Member     Uwe Pilz Join Date: Feb 2017 Location: Leipzig, Germany Posts: 588 Rep Power: 9 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. __________________ Uwe Pilz -- Die der Hauptbewegung überlagerte Schwankungsbewegung ist in ihren Einzelheiten so hoffnungslos kompliziert, daß ihre theoretische Berechnung aussichtslos erscheint. (Hermann Schlichting, 1950)

 Tags sample