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Old   March 14, 2010, 08:03
Question Calculating pressure coefficient in OpenFoam
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Hi all,

I am simulating flow around Onera M6 wing.
How to calculate pressure coefficient around the wing.

Also I want to plot Pressure coefficient at various positions along the length of the wing. how to do it paraview.

regards
mecbe
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Old   December 11, 2010, 07:09
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Hi, if you want to calculate the Cp for later calculate Cl, Cd and Cm, you can do it very simply just adding a few lines in the controlDict file, otherwise I don´t know how to calculate the Cp.

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Old   January 27, 2011, 16:40
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In Paraview is easy.

- Extract Block (the body or wing)
- Plot on Plane Intersection

So it is done!

However, I do not know how to do it with sampling tools of openfoam at command line. Can anyone help?
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Old   January 27, 2011, 19:15
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Hi mecbe2002

Can you post your case? I am interested in external aerodynamics with OpenFOAM.

Basically, you'll haveto rebuilt the wing (vtk files) then with Paraview, you will add "slices" along the wingspan.

Thank you very much,
Minh
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Old   January 28, 2011, 02:51
Default Calculating pressure coefficient in OpenFoam
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hi all,

If you want to calculate the Cp from paraview, do the following procedure

1) convert the simulated results into vtk format
2) install the binary pack of paraview (later versions like 3.4, 3.6 or 3.8)
3) open the converted vtk format of the patches you want to calculate Cp (like wing, airfoil) in paraview
4) In paraview, at the left hand side, there is a function called split vertical command, click on that and click on spreadsheet view
5) after opening spread sheet view select the cells option or point option in paraview on right side of the paraview window
6) in that you wil get the pressures on all the cells on your patch
7) in the paraview window there is an option called file--------->export (export this into cvs file format)
8) open this cvs format in excell sheet and perform the calculations by using the formula Cp=(p-p0)/0.5*rho*v*v for 1 cell and drag all the values there...you wil get cp values for your patch


Regards

Naveen.K.M
CFD Engineer
National Aerospace Laboratories
Bangalore
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Old   January 28, 2011, 04:27
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hi,

regarding the last post: you might want to check for the "calculator" tool ... so you can perform your desired calculus within paraView.

neebwie
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Old   February 16, 2011, 06:39
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[QUOTE=naveen;292587]hi all,


4) In paraview, at the left hand side, there is a function called split vertical command, click on that and click on spreadsheet view

sorry, where are these functions?? i can't find them
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Old   February 16, 2011, 06:51
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for me this option is on the top right of my 3D screen (looks like an open book)

Last edited by mvoss; February 16, 2011 at 09:28.
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Old   April 15, 2012, 18:36
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hi naveen
i am simulating a membrane wing and looking at its aerodynamics . i was wondering how to plot Cp with openfoam itself?
have u got any idea about that?
regards
martin
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Old   April 19, 2012, 07:27
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Quote:
Originally Posted by chathanm View Post
hi naveen
i am simulating a membrane wing and looking at its aerodynamics . i was wondering how to plot Cp with openfoam itself?
have u got any idea about that?
regards
martin
Hello!

You can use gnuplot. Here a theme about how to use it
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Old   April 28, 2013, 10:49
Default how could we draw this cp value then?
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saeideh mohamadi
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Quote:
Originally Posted by naveen View Post
hi all,

If you want to calculate the Cp from paraview, do the following procedure

1) convert the simulated results into vtk format
2) install the binary pack of paraview (later versions like 3.4, 3.6 or 3.8)
3) open the converted vtk format of the patches you want to calculate Cp (like wing, airfoil) in paraview
4) In paraview, at the left hand side, there is a function called split vertical command, click on that and click on spreadsheet view
5) after opening spread sheet view select the cells option or point option in paraview on right side of the paraview window
6) in that you wil get the pressures on all the cells on your patch
7) in the paraview window there is an option called file--------->export (export this into cvs file format)
8) open this cvs format in excell sheet and perform the calculations by using the formula Cp=(p-p0)/0.5*rho*v*v for 1 cell and drag all the values there...you wil get cp values for your patch


Regards

Naveen.K.M
CFD Engineer
National Aerospace Laboratories
Bangalore
hi Naveen
would you please tell us after doing this steps, how could we draw the value of "cp"
as you know these value are foe y axis, what about x axis?
what should we put for x axis to draw the pressureCoeffs?
i am confused, please help me
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Old   April 29, 2013, 00:40
Default Calculating pressure coefficient in OpenFoam
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hi saeidehmohamadim,

In the cvs format you have the values for x axis, check the column by name po (this as same value as x axis) ie chord length wise dimensions....
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Old   April 29, 2013, 13:03
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Quote:
Originally Posted by naveen View Post
hi saeidehmohamadim,

In the cvs format you have the values for x axis, check the column by name po (this as same value as x axis) ie chord length wise dimensions....
thank you very much naveen,
in the .CSV file i have a column with name "p" and also have 3 column with name "point:0" , "point:1" , "point:3" , which point should i use for drawing my pressurecoeffs?

i put my .csv file in the attachment, would you please look at it and tell me what should i do?
i really don't know,thanks a lot again
Attached Files
File Type: gz vtkairfoil.csv.tar.gz (11.4 KB, 32 views)

Last edited by s.m; April 30, 2013 at 02:17.
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Old   April 30, 2013, 00:34
Default Calculating pressure coefficient in OpenFoam
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dear saeidehmohamadim,

You should take the pressure values on only on the airfoil surface from the paraview (.csv) format on.you should take the slice position on the airfoil because it wil be 3D. Can you tell how many points are there in the airfoil surface then i can tell how to plot the cp vs. x/c for airfoil.
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Old   April 30, 2013, 10:10
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Quote:
Originally Posted by naveen View Post
dear saeidehmohamadim,

You should take the pressure values on only on the airfoil surface from the paraview (.csv) format on.you should take the slice position on the airfoil because it wil be 3D. Can you tell how many points are there in the airfoil surface then i can tell how to plot the cp vs. x/c for airfoil.
hi naveen, thank you for guiding me, i take a slice on the surface that airfoil is, but nothing does change. i don't anderstand your question, i put my blockMeshDict and boundary in following:
please tell me how to plot the cp vs. x/c for airfoil, thanks a gain
Attached Files
File Type: txt blockMeshDict.txt (69.5 KB, 34 views)
File Type: txt boundary.txt (1.5 KB, 23 views)
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Old   April 30, 2013, 10:50
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Quote:
Originally Posted by naveen View Post
hi all,

If you want to calculate the Cp from paraview, do the following procedure

1) convert the simulated results into vtk format
2) install the binary pack of paraview (later versions like 3.4, 3.6 or 3.8)
3) open the converted vtk format of the patches you want to calculate Cp (like wing, airfoil) in paraview
4) In paraview, at the left hand side, there is a function called split vertical command, click on that and click on spreadsheet view
5) after opening spread sheet view select the cells option or point option in paraview on right side of the paraview window
6) in that you wil get the pressures on all the cells on your patch
7) in the paraview window there is an option called file--------->export (export this into cvs file format)
8) open this cvs format in excell sheet and perform the calculations by using the formula Cp=(p-p0)/0.5*rho*v*v for 1 cell and drag all the values there...you wil get cp values for your patch


Regards

Naveen.K.M
CFD Engineer
National Aerospace Laboratories
Bangalore
Hi Naveen,
i have a question about the 8) step:
i read in a forum; the pressure value that openFoam gives us after finishing the analysis, is "p/rho" not only "p", is it right?
now my question is,
as i solve the incompressible flow over an airfoil, so the pressure that i give after finishing the analysis is "gauge pressure", therefore the theoretical formula for cp that is
" cp=(p-pinf)/(0.5*rho*Uinlet^2) " is reduced for my analysis to
" cp=(p guage)/(0.5*Uinlet^2) ??

thanks a lot for kind helping
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Old   August 2, 2013, 05:54
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Dear saeidehmohamadi,

I believe you are right, you shall use cp=(p guage)/(0.5*Uinlet^2)

sincerely,

Paulinyi
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Old   August 2, 2013, 05:58
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Quote:
Originally Posted by lfpaulinyi View Post
Dear saeidehmohamadi,

I believe you are right, you shall use cp=(p guage)/(0.5*Uinlet^2)

sincerely,

Paulinyi
Thank you dear luis.
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Old   August 19, 2013, 12:27
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hello s.m can you please tell me here what do you really mean by p gauge i mean when calculating through paraView. thanks !
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Old   August 19, 2013, 13:02
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Quote:
Originally Posted by faraz22 View Post
hello s.m can you please tell me here what do you really mean by p gauge i mean when calculating through paraView. thanks !

Hi
For the incompressible analysis in openFoam, the pressure that is given after finishing the analysis is "gauge pressure" , means "pressure/rho"
because in this analysis openFoam set "gauge pressure /rho" in 0 folder.

But for compressible analysis openFoam set "absolute pressure" in 0 folder, and it also give you "absolute pressure after finishing the analysis, what you see in the paraview.
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