
[Sponsors] 
August 16, 2011, 07:25 
root mean square velocity

#1 
Super Moderator


August 17, 2011, 08:24 

#3 
Senior Member
Matthias Voß
Join Date: Mar 2009
Location: Berlin, Germany
Posts: 446
Rep Power: 13 
switch the post to the fluent branch...?


August 17, 2011, 18:38 

#5 
Super Moderator
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 13,322
Rep Power: 103 
You can do this in CFX using the transient statistics. Look on the output tab in CFXPre.


February 13, 2013, 09:24 

#6  
Member
Mina
Join Date: Apr 2011
Posts: 88
Rep Power: 8 
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

#7 
Member
Mina
Join Date: Apr 2011
Posts: 88
Rep Power: 8 
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 

#8 
Super Moderator
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 13,322
Rep Power: 103 
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  
Member
Mina
Join Date: Apr 2011
Posts: 88
Rep Power: 8 
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 
Super Moderator
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 13,322
Rep Power: 103 
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  
Member
Mina
Join Date: Apr 2011
Posts: 88
Rep Power: 8 
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 
Super Moderator
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 13,322
Rep Power: 103 
Read the documentation on the "velocity correlation uu" variable. It is not the axial velocity.


June 1, 2016, 08:58 
Any suggestions on how to do it?

#13 
New Member
Nazanin Ansari
Join Date: Sep 2013
Posts: 10
Rep Power: 5 
Hello, i want also plot the rms values of the velocity and i am really confused reading this thread:
i don't find the options you named under transient simulation in Output tab by ANSYS CFXPre Is it possible to plot these fluctuations using SST model?  I am also doing the simulations with RSM models, how is that possiblr to plot?  I do not find the variables with Atrnave function! Could you please help me? 

Thread Tools  
Display Modes  


Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
UDF error  parabolic velocity profile  3D turbine  Zaqie  Fluent UDF and Scheme Programming  9  June 25, 2016 19:08 
Fully developed 3d velocity profile: Square inlet!  Taru  FLUENT  6  September 14, 2015 08:38 
help with UDF for contact angle based on contact line velocity  gandesk  Fluent UDF and Scheme Programming  14  October 29, 2012 14:58 
how to compute relative velocity from absolute?  spk  Main CFD Forum  3  July 9, 2010 08:42 
what the result is negatif pressure at inlet  chong chee nan  FLUENT  0  December 29, 2001 06:13 