# Probes location

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 January 27, 2015, 13:43 Probes location #1 New Member   Join Date: Jan 2015 Posts: 5 Rep Power: 2 Dears. I am trying to keep track of the velocity through time in one of my simulations (simplefoam). I am using the probes utility, but the location is working in a different than I thought. I defined a location of (0.013 0 0) in a wall boundary where I have set the boundary condition of (0 0 0) velocity, but I am getting values of velocity different from zero. How can I understand this?

January 27, 2015, 15:30
#2
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Armin
Join Date: Feb 2011
Location: Helsinki, Finland
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Quote:
 Originally Posted by veronica2015 I defined a location of (0.013 0 0) in a wall boundary where I have set the boundary condition of (0 0 0) velocity, but I am getting values of velocity different from zero. How can I understand this?
With the probe utility you cannot specify a point exactly on the boundary; or if you really should manage to set the probe location exactly on the boundary, OpenFOAM will most like crash.

Here some explanations: The probe utility takes a given location and tries to find the cell that contains this location. Meaning the location has to be inside a cell for this to work.
The sampled value at the probe location is then obtained by interpolation. By default the cell center value is interpolated to the probe location, but you can specify different interpolation schemes in probesDict via the keyword interpolationScheme.

So, even if you pick a location that is very close to the boundary (as in your case), OpenFOAM will interpolate the cell value to this location, which may well differ from zero due to the interpolation.

Also note that if you specify your velocity boundary condition as fixedValue, the value will certainly be fixed, so no need to set a probe exactly on the boundary. You can check it in ParaView.

-Armin

 January 27, 2015, 16:05 #3 New Member   Join Date: Jan 2015 Posts: 5 Rep Power: 2 Thank you very much for your explanation

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