# how to plot Cp for unsteady flow past a cylinder

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 April 16, 2013, 20:41 how to plot Cp for unsteady flow past a cylinder #1 New Member   Roger Liu Join Date: Nov 2012 Posts: 8 Rep Power: 5 how to plot Cp for unsteady flow past a cylinder? I use pimpleFoam to calculate Cd and Cl. but how to calculate Cp? and finally plot it vs. X Position Thanks!

 April 16, 2013, 22:49 #2 Senior Member   HECKMANN Frédéric Join Date: Jul 2010 Posts: 237 Rep Power: 9 You can use Paraview to plot this. Just open your case, then use the calculator to compute the Cp by your own. Just apply the formula drom Cp. The calculator looks like this:

 April 16, 2013, 23:20 #3 Senior Member     Ehsan Join Date: Oct 2012 Location: Iran Posts: 2,209 Rep Power: 19 hi What expression for example is suitable for total pressure?

April 17, 2013, 00:04
one more question
#4
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Roger Liu
Join Date: Nov 2012
Posts: 8
Rep Power: 5
Quote:
 Originally Posted by fredo490 You can use Paraview to plot this. Just open your case, then use the calculator to compute the Cp by your own. Just apply the formula drom Cp. The calculator looks like this:
but the Cp I want to plot (vs. X position) is just around the object (e.g. cylinder), how can I capture the pressure value on the cylinder surface??

Thanks!

April 17, 2013, 00:09
#5
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HECKMANN Frédéric
Join Date: Jul 2010
Posts: 237
Rep Power: 9
1) open your case with the wall only (or any patch)
2) use the calculator to get Cp
Cp = (P - P_inf) / (1/2 * rho_inf * V_inf ^ 2)
If you have a decomposed part, you need to select the step 1 (and not 0) to do the calculation. It seems that there is a bug if you use the first step.
3) use the filters -> plot on intersection curve to get the curve.

You can also use the sampling function from openfoam but I never use it so I don't have any example. http://www.openfoam.com/features/run...processing.php
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