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-   -   how to plot Cp for unsteady flow past a cylinder (https://www.cfd-online.com/Forums/openfoam-solving/116309-how-plot-cp-unsteady-flow-past-cylinder.html)

 rogerliu April 16, 2013 20:41

how to plot Cp for unsteady flow past a cylinder

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!

 fredo490 April 16, 2013 22:49

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:
http://www.nti.tul.cz/cz/images/0/09...culator-15.png

 immortality April 16, 2013 23:20

hi
What expression for example is suitable for total pressure?

 rogerliu April 17, 2013 00:04

one more question

Quote:
 Originally Posted by fredo490 (Post 421087) 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: http://www.nti.tul.cz/cz/images/0/09...culator-15.png
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!

 fredo490 April 17, 2013 00:09

3 Attachment(s)
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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