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How to set the inlet velocity profile with fluctuations in Gaussian distribution

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Old   May 11, 2020, 12:38
Default How to set the inlet velocity profile with fluctuations in Gaussian distribution
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gen pei
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Dear All,

I am trying to perform a DNS of the flow over a flat plate (turbulent boundary layer) using StarCCM+.

For the inlet BC, I want to superimpose the time-varying velocity fluctuations in Gaussian distribution on the mean velocity profile. I am just wondering what the best way is to do it in StarCCM+? I can think of two ways that may do the trick, but really need your help to refine the ideas. Please correct me if I made mistake.

1) Using the field function to define the velocity as a function of time. But I am not sure if it is possible to set the fluctuations in Gaussian distribution in StarCCM+. I searched for it at Steve Portal and seems there is no functions/operators can do something like the normal distribution function.

2) Using the Table (x,y,z,t). This approach definitely can work but may be relatively troublesome. I am thinking of using Matlab to generate the whole time-varying velocity profile through the simulation time and import it to the StarCCM+. It should work but seems quite inconvenient as the DNS requires extremely small time step, and the table can easily has large size.

I am wondering if you have any better ideas or advice for this. I really need your insights. Thank you!

Regards,
Gary
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Old   May 11, 2020, 18:53
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Indeed there is no rng in Star field functions. You have to use a table.

An alternative might be to use a .java macro which gives you access to functions in java-land. But I still have no clue how to give random vectors in space and time.

If you are doing no-SGS LES/DES, you have the synthetic turbulence generator which accomplishes the same feat.
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Old   May 11, 2020, 21:13
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Dear LuckyTran,

Thank you so much for the insights. I guess I will try to use the table generated by Matlab.

Regards,
Gary
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Old   May 12, 2020, 02:56
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i would be doing it as a c user function since libraries will also be available in c and it will be very fast and better than a massive imported table
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Old   May 12, 2020, 04:02
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That's honestly a much better idea. It completely crossed my mind since it's a (relatively) newer feature that I haven't used yet.

From the tree diagram, Tools=> User Code and you can import a library. You should be able to yoink a code from somewhere with relative ease.


Knowing this, now I am excited because there are a bunch of functions I've been wanting to code for Star. =)
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Old   May 12, 2020, 04:12
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glad to remind you and the feature has been there for at least a decade after looking at some old c++ ucode of mine
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Old   May 18, 2020, 22:38
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Dear Ping,

Thank you so much for your reply. It is extremely helpful!

Regards,
Gen Pei
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dns, inlet boundary condition, turbulent inflow, velocity fluctuations

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