STRANGE BUT REAL !!!!about the velocity at wall BCs

mohammad · September 4, 2014, 22:54

Hello everyone,

I was trying to explore some simple thing.
I created a simple duct, and then simple inlet outlet and walls.
amazingly, when I extracted the nodal velocity values on all wall BCs using FILE>Export>.... , they are not zero.!!!! ( walls are no-slip, though)

I extracted the velocity contours on the wall, they are zero. I shared this problem with my supervisor. and he told me that they values are being calculated on each cell centet point and then interpolated on the vertices...

Is that correct???

cfdseeker · September 5, 2014, 04:59

Yes, the at the walls are represented by volumes and actual boundaries of these volumes away from walls. So you see velocity on the wall. If you want it zero, choose hybrid velocity instead of conservative in CFD Post. http://www.cfd-online.com/Wiki/Ansys..._inaccurate.3F

ghorrocks · September 5, 2014, 06:41

I think the FAQ you were trying to reference was this one: http://www.cfd-online.com/Wiki/Ansys...t_the_walls.3F

September 4, 2014, 22:54	STRANGE BUT REAL !!!!about the velocity at wall BCs	#1
mohammad Senior Member mohammad Join Date: Dec 2010 Location: UK Posts: 245 Rep Power: 16	Hello everyone, I was trying to explore some simple thing. I created a simple duct, and then simple inlet outlet and walls. amazingly, when I extracted the nodal velocity values on all wall BCs using FILE>Export>.... , they are not zero.!!!! ( walls are no-slip, though) I extracted the velocity contours on the wall, they are zero. I shared this problem with my supervisor. and he told me that they values are being calculated on each cell centet point and then interpolated on the vertices... Is that correct??? Last edited by mohammad; September 5, 2014 at 05:30.

September 5, 2014, 04:59		#2
cfdseeker New Member Join Date: Aug 2014 Posts: 15 Rep Power: 11	Yes, the at the walls are represented by volumes and actual boundaries of these volumes away from walls. So you see velocity on the wall. If you want it zero, choose hybrid velocity instead of conservative in CFD Post. http://www.cfd-online.com/Wiki/Ansys..._inaccurate.3F mohammad likes this.

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September 5, 2014, 06:41		#3
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,696 Rep Power: 143	I think the FAQ you were trying to reference was this one: http://www.cfd-online.com/Wiki/Ansys...t_the_walls.3F