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April 23, 2009, 05:01 |
Velocity profiles near walls?
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#1 |
New Member
Join Date: Mar 2009
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Hi,
I ran in the last days some simulations in pipe geometries. In ParaView I to wanted to plot the velovity profiles (y: Velovity, x: Radius). In the center of the tube everything worked great. But near the walls I had a region where the velocity was everywhere the same. I thought I had a problem with my simulation. So I took the tutorial cavity for icoFoam, altered it a bit to see the profile well and ran it. The same profile. In the centre was everything good and nearer to the walls I had a jump to the wall velocity. Actually I expected a smooth raise of the velocity to the wall. In my simulation the geometry is much smaller and the region near the wall therefore much bigger than here. Thats not what I expected or what it should be. I attached the two pictures with the profiles and marked the regions. Thanks for help. |
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April 23, 2009, 10:03 |
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#2 |
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Problem solved....almost.
When I use Sample from OpenFoam and import the Data to Excel I get a good smooth profile. Do not know why ParaView creates such profiles. Any sugestions why? |
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April 23, 2009, 11:09 |
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#3 |
Senior Member
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Hi Hectux,
Try to increase the number of points in the x-y plot, and see if it helps. Regards, Jose Santos |
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April 23, 2009, 15:37 |
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#4 |
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Yes. Thats probably the problem. But I cannot find the funkction to increase the number of points.
With SampleDict it was no problem to set 10 oder 500 points. |
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April 24, 2009, 05:46 |
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#6 |
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Ok.
First there is an example file of SampleDict in $FOAM_UTILITIES/postProcessing/sampling/sample There is a complete SampleDict file with every functions. You will find a better description in the UsersGuide of OpenFOAM. The SampleDict is saved in the system folder. Often you have to create a file on your own: My SampleDict is quite simple but it works well for me: /*--------------------------------*- C++ -*----------------------------------*\ | ========= | | | \\ / F ield | OpenFOAM: The Open Source CFD Toolbox | | \\ / O peration | Version: 1.5 | | \\ / A nd | Web: http://www.OpenFOAM.org | | \\/ M anipulation | | \*---------------------------------------------------------------------------*/ FoamFile { version 2.0; format ascii; class dictionary; object sampleDict; } // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * // interpolationScheme cellPoint; setFormat raw; sets ( profile { type uniform; axis y; start (0 -5e-4 2e-3); end (0 5e-4 2e-3); nPoints 500; } ); surfaces (); fields ( U ); // ************************************************** *********************** // What it does: Creates a line with evenly distributed 500 points. Start point (0 -5e-4 2e-3) end points (0 5e-4 2e-3). Thats a cut through the center of my pipe. With fields: U I get a file which I can import to e.g. Excel or Spreadsheet. So I have 4 colums. First: The coordinates of my points, second: Ux component of the velocity vector in that point, third: Uy, fourth Uz. I had to change the punctuation from "." to "," in Excel but that should be no problem, I think ;-) |
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April 24, 2009, 09:35 |
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#7 | |
Senior Member
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Quote:
Regards, Jose Santos |
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April 24, 2009, 19:33 |
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#8 |
Member
Nugroho Adi
Join Date: Mar 2009
Location: norway
Posts: 79
Rep Power: 17 |
Dear Hectux
thanks for your tutorial, thousand thanks. regarding plotting, maybe you can use xmgrace tool sudo apt-get install xmgrace this software really easy to use compare excell (at least for me) |
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May 20, 2009, 10:37 |
help with xmgrace
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#9 |
Member
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Hello Hectux,
I read your post and have not been able to get xmgrace to plot anything. I installed and when I run a sampledict and have sets files filled, I run xmgrace and the postprocessing window opens, however, i am not able to bring up any plots? Can you say what is needed to get the data showing? Thanks for any advice, Lori Holmes |
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May 21, 2009, 10:42 |
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#10 |
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Sorry, I am not using xmgrace. I am still using Excel.
I suggest you write mahaputra an private message. |
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May 21, 2009, 10:49 |
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#11 |
Member
Nugroho Adi
Join Date: Mar 2009
Location: norway
Posts: 79
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Hei lth
follow this : Use: Data/Import/ASCII. Choose the logs directory and remove '.dat' from the filter. Then you can plot whatever you like in the logs directory. hope this help cheers |
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May 21, 2009, 10:51 |
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#12 | |
Member
Nugroho Adi
Join Date: Mar 2009
Location: norway
Posts: 79
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Quote:
http://www.cfd-online.com/Forums/ope...-plotting.html |
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