# Urms of Vertical Velocity

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 November 28, 2013, 05:38 Urms of Vertical Velocity #1 New Member   Join Date: Nov 2013 Posts: 2 Rep Power: 0 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?

 December 5, 2013, 03:48 #2 New Member   Join Date: Nov 2013 Posts: 2 Rep Power: 0 Anybody can help me on this?

December 6, 2013, 12:10
#3
Senior Member

Jamal Foroozesh
Join Date: Oct 2012
Location: Iran
Posts: 141
Rep Power: 7
Quote:
 Originally Posted by hct Anybody can help me on this?

Best Regards

Jamal

 November 17, 2014, 11:51 hi #4 Member   Qureshi M Z I Join Date: Sep 2013 Posts: 75 Rep Power: 6 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

 November 17, 2014, 14:19 #5 New Member   Join Date: Nov 2013 Posts: 11 Rep Power: 5 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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