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Velocity Fluctuations in Fluent

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Old   March 19, 2009, 02:30
Exclamation Velocity Fluctuations in Fluent
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Andrew
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Hi Everyone.

I'm running simulations using Fluent 6.2.16 for flow over an elastically mounted circular cylinder. I want to monitor and write to file the velocity fluctuations u', v' and w', but cannot seems to find these options anywhere within Fluent. I see that you can monitor the absolute velocity and relative velocities in all directions, but no fluctuations.

Does anybody know how I can monitor and record these parameters during a simulation? Are they available in the GUI within Fluent, or do I have to create an UDF to obtain the values?

Thanks.

Andrew
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Old   March 20, 2009, 03:31
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User Defined Function (UDF)?
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Old   March 20, 2009, 05:05
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Hi Paka,

Yeah, I meant User Defined Function.

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Old   March 20, 2009, 05:35
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That's what I'm saying, read tutorials about UDF, finally the idea should show up, unless someone else on this forum can provide you ready to go solution.

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Old   March 20, 2009, 05:38
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Thanks Paka.

I'll try to read through the UDF tutorials and manual to see if there is anything relating to fluctuating velocities.

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Old   March 21, 2009, 14:40
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what if you just monitor the absolut velocities and then calculate the deviations yourself by substracting the time-mean-value or simple doing a DFT on it? Is that what you want?

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Old   March 22, 2009, 17:17
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That's what I was thinking. As soon as you get familiar with UDF (which might look scary at the beginning), it should be relatively easy to write your own routine. It is easy to access velocity data, so this shouldn't be a big deal.

If you do not work on UNIX system, it means you use Windows, which means you need Microsoft C compiler, which means you need to spend money and get it - I absolutely do not support that idea . In this case, I would just dump velocity data into text file and then do post-processing on your own writing for example simple Python script.

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Old   March 22, 2009, 22:41
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Thanks Guys,

I appreciate the feedback. I will try to monitor the velocities into text files and post-process the data for fluctuating velocities using DFT or another method. This seems like the easiest option that Fluent will allow.

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