Urms of Vertical Velocity

hct · November 28, 2013, 04:38

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?

hct · December 5, 2013, 02:48

Anybody can help me on this?

jamalf64 · December 6, 2013, 11:10

Quote:

Originally Posted by hct

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

m zahid · November 17, 2014, 10:51

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

danielfc · November 17, 2014, 13:19

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.

November 28, 2013, 04:38	Urms of Vertical Velocity	#1
hct 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?

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December 5, 2013, 02:48		#2
hct New Member Join Date: Nov 2013 Posts: 2 Rep Power: 0	Anybody can help me on this?

November 17, 2014, 10:51	hi	#4
m zahid Member Qureshi M Z I Join Date: Sep 2013 Posts: 79 Rep Power: 12	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, 13:19		#5
danielfc New Member Join Date: Nov 2013 Posts: 11 Rep Power: 12	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.