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August 16, 2011, 07:25 
root mean square velocity

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August 17, 2011, 08:24 

#3 
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Matthias Voß
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switch the post to the fluent branch...?


August 17, 2011, 18:38 

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Glenn Horrocks
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You can do this in CFX using the transient statistics. Look on the output tab in CFXPre.


February 13, 2013, 09:24 

#6  
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Mina
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Quote:
I need to plot rms value of the stream wise velocity fluctuation in my fluid domain(√(u' u' )) . since before running the transient case i specify velocity in the transinet statistics. so in my variables i have velocity correlation uu.Trnavg. is that sqrt(velocity correlation uu) representing (√(u' u' )) ? 

February 13, 2013, 09:28 
phase averaging data in CFX

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Mina
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another question:
when you specify velocity or other variables in the transinet statistics. in variables you have variable.Trnavg. which means data has been average over the whole simulated time. but if you want to do phase averaging or make data averaged over just few periods of time is that possible? 

February 13, 2013, 18:12 

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Glenn Horrocks
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If you want only partial time averaging or phase averaging you will have to export it and do it yourself.


February 14, 2013, 06:53 

#9  
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Mina
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Quote:
what about "velocity correlation uu" is that representing (u' u' )? or is sqrt(velocity correlation uu. Trnavg) representing (√(u' u' ))? i want to plot the rms value of velocity fluctuation, is that the right way? Last edited by Mina_Shahi; February 14, 2013 at 07:17. 

February 14, 2013, 17:12 

#10 
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Glenn Horrocks
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If you are using a turbulence model then you can get u'u' from the turbulence intensity or the Reynolds Stresses (if a RSM). You can also do the Trnavg functions on these variables.
Be careful with averaging of these functions. Note that sqrt(transient average(u'u')) does NOT equal transient average(sqrt(u'u')). 

February 17, 2013, 06:40 

#11  
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Mina
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Quote:
thank you for your answer, i am a bit confused with that! in the Transient statistics there are different options: 1/ Arithmetic Average 2/ Root Mean Square and .... In my transient simulation i used the first option Arithmetic Average and then as a variable i selected velocity ... now as i mentioned previously i am interested in the rms axial velocity. so i am plotting the sqrt(velocity correlation uu. Trnavg) which i am not sure if it gives me rms axial velocity or not ! that is my first question !!! i think i had to go for the Root Mean Square in the Transient statistics option, am i right? if the transient calculation finished is that a way to get Root Mean Square values? which one i should look for? apparently sqrt(velocity correlation uu. Trnavg) gives sqrt(transient average(u'u')) 

February 17, 2013, 06:50 

#12 
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Glenn Horrocks
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Read the documentation on the "velocity correlation uu" variable. It is not the axial velocity.


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