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Old   March 4, 2008, 09:15
Default Vorticity Direction
  #1
Sham
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Hi all,

I am simulating an oscillating cylinder and observing the vorticities. Does anyone know how to view the velocity in which the clock wise and anti clockwise vorticity direction gives you diff colour in the contour plot? This will make it easy to differentiate between positive and negative vorticity direction.

Sham
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Old   March 4, 2008, 23:47
Default Re: Vorticity Direction
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NRD
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Hello,

Your question is not entirely clear to me. However, if you want to look at the direction in which the vortices are rotating (i.e. whether clockwise or counter-clockwise) why not plot the velocity vectors?
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Old   March 7, 2008, 01:58
Default Re: Vorticity Direction
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John Young
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Hi Sham, I'm assuming your problem is 2D, where fluent only provides the vorticity magnitude. To get around this you can define a Custom Field Function (see sect 30.5.1 of the user guide) for the vorticity which is du/dy - dv/dx. John
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Old   March 22, 2008, 04:41
Default Re: Vorticity Direction
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Sham
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John,

Could you pls explain a little bit more how can I use the Custom Field Function to define the vorticity direction and show it in diff colour? I am modelling a 2D cylinder in free stream.

Sham.
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Old   March 24, 2008, 17:15
Default Re: Vorticity Direction
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John Young
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Hi Sham,

Go to the "Define" menu, pick "Custom Field Function". Then in the "Field Functions" drop-down box, pick "Derivatives", select "dX-Velocity/dy" from the second drop-down box, click "Select", then the "-" button, then select "dY-Velocity/dx" and click "Select".

Now choose a name for your new variable (e.g. "Vorticity-signed"), then click "Define".

When you go to plot contours, choose "Custom Field Functions", and your new variable will be available. Note that most of the vorticity will be in the boundary layer, so you will probably have to take it off "Auto Range" and pick some lower values to see anything at all in the wake. Positive values represent rotation in one direction, negative values in the other.

Hope that helps, John

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Old   March 25, 2008, 00:08
Default Re: Vorticity Direction
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Sham
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John,

Thanks a lot. It works.

Sham.
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Old   May 19, 2011, 16:27
Question VORTICITY calculation in unstructured grid?
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anil
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I have one doubt regarding the vorticity calculation in FLUENT. In a forum i found the vorticity calculation is by du/dy-dv/dx. But this is valid for structured mesh only according to theory and how can it be valid for unstructured grids. Is there any method (Algorithm) by which Fluent calculates the vorticity for unstructured grid?.
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