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Plotting pressure difference contour at a surface

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Old   April 26, 2017, 11:15
Question Plotting pressure difference contour at a surface
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Pedro Zaterka
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Hello, I'm new to this forum, so sorry if this post doesn't quite meet with the standard ones here.

Nevertheless, I'm analysing a thin structure in ANSYS CFX and comparing it to a real wind tunnel result, the problem is that I need to get the difference between the pressures on the upper and bottom faces. I have already created different Named Selections for both faces, but I can't find the right CEL expression to plot the result I need.

I was thinking about an expression being the pressure at a surface at a coordenate (x1,y1, z1(Coordenate of the surface on that point)), z being the vertical axys for this analysis, minus the pressure at the other surface at the same (x1,y1, z2(Coordenade of the other surface)) but I couldn't quite find how to write it in the Expression tab. Also, the coordenate on the Z axys varies along the faces.

I also tried exporting it to Static Structural but I can't plot the contour for resulting applied pressure there, it only shows the vectors I've imported for each case (I applied both pressures on the upper face of the elements). Ploting on Ansys APDL also was shown unsuccesfull, so I think the answer is in CFD-Post.

To make it easy to visualize, I'm attaching the plotted pressure contours on both upper and bottom faces, as well as the named selections used. The ones I'm interested are "RooftopTop" and "RooftopBottom".

Named Selections:
Attachment 55614

Pressure contour at "RooftopBottom":
Attachment 55615

Pressure contour at "RooftopTop":
Attachment 55616

Thanks in advance,
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Old   April 26, 2017, 18:38
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Glenn Horrocks
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Your question is welcome. Your image attachments did not work, a FAQ on attaching images is here:

An easier way of doing this might be to do it in post-processing. In CFD-Post you could select the upper or lower surface and export the pressure data and nodal locations. You can then analyse this elsewhere to compare against your experimental results. But you will only be able to do this for time steps where you have saved a results file (including the mesh).
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cel, cel functions, pressure difference, structures

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