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Urms of Vertical Velocity

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Old   November 28, 2013, 05:38
Default Urms of Vertical Velocity
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hct
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I am running a steady state CFD of windflow over a process plant.

I would like to track the root-mean-square of vertical velocity or the standard deviation of vertical velocity fluctuations in FLUENT.

However, there is no such option in FLUENT.

Since we know that

U'=√(1(u_x'^2+u_y'^2+u_z'^2)/3)=√(2k/3) , where k = turbulent kinetic energy

and that for RANS model (what I am using) assumes isotropic reynold stresses (where u_x'=u_y'=u_z') , we can come to the following formula,

√(1(3u'^2)/3)=√(2k/3)
k=3u^2/2

Which means that if i am looking for a standard deviation of vertical velocity fluctuation value of 1.75m/s, I can look for a value of 4.59 J/kg in the turbulent kinetic energy plot.

Am I interpreting this correctly?
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Old   December 5, 2013, 03:48
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Anybody can help me on this?
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Old   December 6, 2013, 12:10
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Jamal Foroozesh
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Quote:
Originally Posted by hct View Post
Anybody can help me on this?
You must run your simulation unsteady. in unsteady problems, fluent have Urms in "unsteady statistics" option.
I hope this help you.

Best Regards

Jamal
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Old   November 17, 2014, 11:51
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Qureshi M Z I
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i want to calculate the Reynolds stresses (space averaging) at steady state . if any body know the steps in fluent or any book and reference material. please share this.
thanks

regards
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Old   November 17, 2014, 14:19
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hct,

Maybe it is too late to help you, but considering your question, it seems like you are dealing with helideck design, since CAP437 recommends a maximum vertical velocity standard deviation criterion of 1,75m/s.

Your interpretation of the kinetic turbulent energy is reasonable and I have used the same approach in the paper OMAE2010-20686, including comparisons with experiments. My advice is to use this simplification carefully, since it gives you a good overview of the turbulence field, but it may result in large errors if considered locally.
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