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Old   April 28, 2013, 04:55
Default plot cp on airfoils
  #1
s.m
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saeideh mohamadi
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hi everyone,
i wana plot the pressureCoeffs on NACA4412 airfoil, i resd in the forum that i can use PlotOnIntersectionCurves in paraview, my question is that, how can i use PlotOnIntersectionCurves in paraview? i don't know what normal i should use, x y or z ? i put my VTK file of the airfoil and the forceCoeffs on it in the following, would you please please give me some advice to use PlotOnIntersectionCurves? thank you very very much
Attached Images
File Type: jpg sss.jpg (21.9 KB, 31 views)
Attached Files
File Type: gz airfoil_airfoil.tar.gz (17.8 KB, 17 views)
File Type: gz forceCoeffs.tar.gz (6.5 KB, 16 views)
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Old   April 28, 2013, 08:53
Default plot cp on airfoils
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saeideh mohamadi
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Quote:
Originally Posted by musahossein View Post
Many thanks for your explanation. Now I get the picture.
hi musahossein and wyldckat
i am working on airfoils and i need to plot the "pressureCoeffs" on the airfoil. as you said i add these lines to my controlDict and i get the result with two format vtk and raw for the latestTime,i'll put them in attachment, how should i plot this result???
please help me
wallPressure
{
type surfaces;
functionObjectLibs ("libsampling.so");
surfaceFormat raw; // vtk;
outputControl outputTime;
interpolationScheme cellPoint;

fields (
p
);
surfaces
(
airfoil_airfoil
{
type patch;
patches ("airfoil.*");
interpolate true;
triangulate false;
}
Attached Files
File Type: gz p_airfoil_airfoil.vtk.tar.gz (8.2 KB, 19 views)
File Type: gz p_airfoil_airfoil.raw.tar.gz (5.5 KB, 8 views)
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Old   April 28, 2013, 10:36
Default plot cp on airfoils
  #3
s.m
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saeideh mohamadi
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hi Dear Foamers
anybody isn't here to say me how can i plot "pressureCoeffs" on a airfoil?????
i am tired of looking for the answer of this question everywhere
i found many way to plot this figure but none of didn't give me a final result.
please please help me,
thank you very much
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Old   April 28, 2013, 13:28
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Bruno Santos
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Hi Saeideh Mohamadi,

I moved the second post from sampleDict and controlDict and the first one from the ParaView forum, because you've opened this new thread and it made more sense to keep these questions together.

  1. Start ParaView and open the VTK file you attached.
  2. Select the item "p_airfoil_airfoil.vtk" on the "Pipeline Browser".
  3. Then on the menu, choose "Filters -> Alphabetical -> Plot On Intersection Curves".
  4. Click on the "Y Normal" button and then on the "Apply" button.
  5. Attached is an example of what it looks like.
Best regards,
Bruno
Attached Images
File Type: jpg Screenshot from 2013-04-28 17:23:04.jpg (46.1 KB, 136 views)

Last edited by wyldckat; April 28, 2013 at 13:33. Reason: more info on the moves
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Old   April 29, 2013, 13:16
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saeideh mohamadi
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Quote:
Originally Posted by wyldckat View Post
Hi Saeideh Mohamadi,

I moved the second post from sampleDict and controlDict and the first one from the ParaView forum, because you've opened this new thread and it made more sense to keep these questions together.

  1. Start ParaView and open the VTK file you attached.
  2. Select the item "p_airfoil_airfoil.vtk" on the "Pipeline Browser".
  3. Then on the menu, choose "Filters -> Alphabetical -> Plot On Intersection Curves".
  4. Click on the "Y Normal" button and then on the "Apply" button.
  5. Attached is an example of what it looks like.
Best regards,
Bruno
hi wyldckat, thanks a lot, i did what you said me, and i get a figure similar to your fingure.
i have a question from the figure that is resulted from "Plot On Intersection Curves" in the paraview, what is the value of x axis stand for?
is it chord length? i mean your chord length is 2.5 that the x axis show us 2.5?
i want comparison my result with experimental result, so i need to figure that "y axis" is "pressureCoeffs" and the "x axis" is e.g "x/chord" if the chord is along the x axis.
thanks again for giving me advise dear wyldcka
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Old   April 29, 2013, 18:28
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Hi Saeideh Mohamadi,

Sorry, I forgot to mention that you can configure in the tab "Display", the values to be plotted on the graph. There you can choose what values to be used for X and what values to be used for Y.

As for calculating specific values, such as the "x/chord", you'll need to first apply the filter "Calculator". In other words:
  1. Open the VTK file.
  2. Apply the filter "Calculator" and specify that you want to calculate "CoordsX/2.5".
  3. Then apply the filter "Plot On Intersection Curves".
For more information about the "Calculator" filter: http://www.paraview.org/Wiki/ParaVie...ide/Calculator

Best regards,
Bruno
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Old   April 30, 2013, 10:43
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saeideh mohamadi
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Quote:
Originally Posted by wyldckat View Post
Hi Saeideh Mohamadi,

Sorry, I forgot to mention that you can configure in the tab "Display", the values to be plotted on the graph. There you can choose what values to be used for X and what values to be used for Y.

As for calculating specific values, such as the "x/chord", you'll need to first apply the filter "Calculator". In other words:
  1. Open the VTK file.
  2. Apply the filter "Calculator" and specify that you want to calculate "CoordsX/2.5".
  3. Then apply the filter "Plot On Intersection Curves".
For more information about the "Calculator" filter: http://www.paraview.org/Wiki/ParaVie...ide/Calculator

Best regards,
Bruno
hi Bruno, thank you very much for kind guiding us

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 i have a question,
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) ?
i mean that for using the calculator that is in the paraview, i should write
" p/0.5*Uinlet^2" ?
your answer really help me, thanks again Bruno.
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Old   April 30, 2013, 18:52
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Hi Saeideh,

Yes, in incompressible solvers the "p" field is actually "pressure/rho" and it is relative to the global pressure, so basically it is "pressure gauge / rho" as you wrote.

And yes, it makes perfect sense the symbolic calculation you've made... although you forgot the parenthesis on the last equation:
Code:
p/(0.5*Uinlet^2)
Best regards,
Bruno
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Old   May 1, 2013, 13:09
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saeideh mohamadi
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Quote:
Originally Posted by wyldckat View Post
Hi Saeideh,

Yes, in incompressible solvers the "p" field is actually "pressure/rho" and it is relative to the global pressure, so basically it is "pressure gauge / rho" as you wrote.

And yes, it makes perfect sense the symbolic calculation you've made... although you forgot the parenthesis on the last equation:
Code:
p/(0.5*Uinlet^2)
Best regards,
Bruno
tank you very very much Dear Bruno
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Old   December 3, 2013, 10:21
Default plot cp on airfoils
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Hello

I tried to follow the instructions of this thread.

Poorely I get an error-message when I use Saeideh MohamadiŽs code for the wallPressure function.
The Run-time Post-processing code:
Code:
wallPressure
      {
        type surfaces;
        functionObjectLibs ("libsampling.so");
        surfaceFormat vtk; // raw;
        outputControl timeStep;
        outputInterval 2;
        interpolationScheme cellPoint;

        fields (p);
      surfaces (BLADE
        {
           type patch;
       patches ("BLADE");
         interpolate true;
         triangulate false;
       } ); }
The error-message:
Code:
--> FOAM FATAL ERROR: 
More than one patch accessing the same transform but not of the same sign.
patch:SYM1 transform:0 sign:1  current transforms:(1 0 0)

    From function Foam::label Foam::globalIndexAndTransform::addToTransformIndex
(
const label,
const label,
const bool
) const

    in file lnInclude/globalIndexAndTransformI.H at line 240.

FOAM exiting
The error message refers to one of my periodic boundaries "SYM1"
I get the same error message when I use foamToVTK. So I wonder how to get the surface-information of the airfoil!

My questions now are:
1. How can I make wallpressure work or anyhow get information of the surface-pressure, or if the next one is easier to solve
2. Is there another possibility to plot cp on airfoils

Thank you very much

Best regards Tobi

Last edited by Tobias Adam; December 4, 2013 at 08:49.
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Old   December 11, 2013, 11:05
Wink Next problem to be solved
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Hey
I solved my problem as I did not do the steps with the VTK-file, but with my normal Foam-file.
To be sure to get the data of the airfoil I only activated the mesh-region "BLADE" in the mesh-region window.
I generated Values for cp with the calculator filter and did the Plot On Intersection Curves as described above.

Poorely I still donŽt know how to rescale the x-axis, so that I get x/chord-length ( y/chord-length for my case).
Furthermore IŽd like to plot the graphs for the suction- and pressure-side separately (in one diagram).
Is there any possibility to do so?

Best regards Tobi
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Old   January 5, 2014, 16:38
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Greetings Tobias,

Quote:
Originally Posted by Tobias Adam View Post
Poorely I still donŽt know how to rescale the x-axis, so that I get x/chord-length ( y/chord-length for my case).
Furthermore IŽd like to plot the graphs for the suction- and pressure-side separately (in one diagram).
Is there any possibility to do so?
In theory:
  1. Use the calculator to calculate the position over X by the chord value, as shown in the first attachment.
  2. In the second attachment is shown how to configure the first plot.
  3. In the third attachment is shown how to configure the second plot. You can rename the name for the legend. Simply double click on the name under the column "Legend Name".
Best regards,
Bruno
Attached Images
File Type: jpg Screenshot from 2014-01-05 20:34:33.jpg (48.8 KB, 49 views)
File Type: jpg Screenshot from 2014-01-05 20:35:16.jpg (48.0 KB, 48 views)
File Type: jpg Screenshot from 2014-01-05 20:35:19.jpg (48.2 KB, 42 views)
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Old   January 15, 2014, 09:18
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Hello everyone :-)

Thank you Bruno for your help! I still didnŽt achieve to seperate the two plots, but nevertheless the plot looks quite good.

IŽve got one last question to this topic:

Is there a possibility to get the data arrays, which are used for the plot, as coupled point data in a data sheet with two rows? One row for the cp and one for the y/chord?
IŽd like to use it in a calculator program like excel to compare my cp values with values from older simulations.

Thanks for your help!

Best regard Tobias :-)
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Old   January 16, 2014, 15:57
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Hi Tobias,

Quote:
Originally Posted by Tobias Adam View Post
Is there a possibility to get the data arrays, which are used for the plot, as coupled point data in a data sheet with two rows? One row for the cp and one for the y/chord?
IŽd like to use it in a calculator program like excel to compare my cp values with values from older simulations.
Have you tried:
  1. Select the plot data entry on the "Pipeline Browser", respective to the plot you are seeing.
  2. Menu -> File -> Save Data
  3. Save as ".csv"
  4. Open the CSV file in Excel or Open/LibreOffice Calc.
Best regards,
Bruno
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Old   January 17, 2014, 08:18
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Tobias Adam
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Hi Bruno,

Thanks again for your advice, it helped me a lot!
IŽm sorry for making demands on your time! This problem was realy easy to solve!

Kind regards,
Tobi
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