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Karman vortex - steady state solution with RANS ?

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Old   September 27, 2018, 14:46
Default Karman vortex - steady state solution with RANS ?
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Hi,

I am wondering if I can get a steady simulation of a karman vortex simulation?

So in reality this phenomenon is highly unsteady. But in my CFD I am not interested to see the vortex. I am interested in getting a steady state solution.

Is this possible with RANS?

If I look at this video:
https://www.youtube.com/watch?v=57-URbKeWME

I think I will always see some vortex and vortex detachment, even in a RANS?

So if I am interested in an steady solution I should calculate maybe with URANS and take the mean of my velocities over time?

Thank you for your help

Cellzone
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Old   September 27, 2018, 16:16
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Quote:
Originally Posted by CellZone View Post
Hi,

I am wondering if I can get a steady simulation of a karman vortex simulation?

So in reality this phenomenon is highly unsteady. But in my CFD I am not interested to see the vortex. I am interested in getting a steady state solution.

Is this possible with RANS?

If I look at this video:
https://www.youtube.com/watch?v=57-URbKeWME

I think I will always see some vortex and vortex detachment, even in a RANS?

So if I am interested in an steady solution I should calculate maybe with URANS and take the mean of my velocities over time?

Thank you for your help

Cellzone

Yes, the RANS formulation is based on a statistically averaging that makes the solution steady.
In a similar way, you could consider the example of the laminar vortex shedding with alternating vortices. If you perform explicitly the time average of the transient solution, you will get a steady solution with two symmetric vortices.
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Old   September 28, 2018, 02:18
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RANS eliminates (real) turbulence, but ist dies not eliminate vortices at all. You may use for your task.
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Old   September 28, 2018, 04:01
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RANS eliminates (real) turbulence, but ist dies not eliminate vortices at all. You may use for your task.


That depends on the solver - if the steady RANS equations are used or not.
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Old   September 28, 2018, 04:11
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RANS means one solves always the statistically steady averaged variable, URANS introduces a time variation of the mean variable. However that does not mean that the two formulations are similar in the modelling.
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