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Old   June 16, 2010, 06:05
Default Circulation
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I am simulating a 3D piston/cylinder vortex ring generator in ANSYS CFX. I wonder how can I calculate the circulation in CFX? I want to calculate the vortex ring circulation and the total circulation discharged fron the piston.
The renolds number is higher than 2000

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Old   June 16, 2010, 08:28
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Can you describe what you are trying to model? A drawing would help.
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Old   June 16, 2010, 09:15
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In this article (ref. pic:0) they have done it experimentally. I want to do it in ANSYS CFX. pic 1 is the schematic of the apparatus. the vortix ring is in pic 2. in pic three the vector velocity field and vorticity contour is there. and pic 4 shows the circulation.
I want to know how can i calculate circulation in cfx.

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File Type: jpg 1.JPG (24.3 KB, 50 views)
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File Type: jpg 4.JPG (51.5 KB, 46 views)
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Old   June 16, 2010, 18:41
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So you have done the simulation and you want to post-process the results to get a representative circulation? The paper you refer to should define how they measure circulation. You will have to use their definition for comparable results.
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Old   June 16, 2010, 20:41
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They define it in this way:
"For each case, the maximum circulation of the vortex formed (of either positive or negative sense) was
measured by integrating the vorticity within an iso-vorticity contour (of a given sense)
of 1 s
1."

But I dont know how to do it in ANSYS CFX?
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Old   June 16, 2010, 20:48
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This is all stuff you can do in CFD-Post.

Make a user surface defined by a contour of vorticity=1 [1/s]. Then do a surface integral of vorticity on that user surface using the function calculator. Easy.
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Old   June 17, 2010, 01:21
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thank you very much for yur help.
So if I get you correctly:
I define a plane and plot vorticity on that plane (with the vorticity magnitude of 1 s-1)
then I should define the integral of vorticity on that contour.

can you please tell me how do I define the surface integral for vorticity in the calculator of cfd-post?

Once again thanks for your help
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Old   June 17, 2010, 08:20
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The CFX tutorials show how to do this sort of post processing.
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Old   June 17, 2010, 22:15
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Do you know any tutorial on this i could look?
I would appreciate it if you can refernce any to me

regards
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Old   November 23, 2012, 07:03
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"For each case, the maximum circulation of the vortex formed (of either positive or negative sense) was
measured by integrating the vorticity within an iso-vorticity contour (of a given sense)
of 1 s
1."

If I am not mistaken you should be able to define an iso-surface which is defined my vorticity magnitude. This should then be coloured by surface integral or area integral of vorticity magnitude. The area or surface integral of the vorticity may be defined as an expression and then a scalar variable if it is not present in the set of standard results.


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