CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Software User Forums > ANSYS > FLUENT

velocity fluctuations for an unsteady simulation

Register Blogs Members List Search Today's Posts Mark Forums Read

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   March 11, 2011, 17:33
Default velocity fluctuations for an unsteady simulation
  #1
New Member
 
Join Date: Dec 2010
Posts: 13
Rep Power: 15
ajkratos is on a distinguished road
hi
is there any way in fluent to find velocity fluctuations to calculate turbulence kinetic energy for a transient/unsteady simulation? thanks
ajkratos is offline   Reply With Quote

Old   March 12, 2011, 06:31
Default
  #2
Senior Member
 
xrs333
Join Date: Aug 2010
Posts: 125
Rep Power: 16
xrs333 is on a distinguished road
Hi, you are actually talking about DNS of turbulent flow.
xrs333 is offline   Reply With Quote

Old   March 12, 2011, 07:00
Default
  #3
New Member
 
Join Date: Dec 2010
Posts: 13
Rep Power: 15
ajkratos is on a distinguished road
No I am performing LES and in post processing i only get an option for sub grid scale turbulence. So i figured out if i have velocity fluctuations i can calculate TKE using equation 1/2(u'^2+v'^2+w'^2) where u',v' and w' are the fluctuating components of the velocity. I also know that i can get fluctuating components by using u'=u-ubar where u is instanteanous velocty and ubar is the time averaged velocity. I m just not sure how to do it in fluent.
ajkratos is offline   Reply With Quote

Old   March 12, 2011, 07:13
Default
  #4
New Member
 
Join Date: Dec 2010
Posts: 13
Rep Power: 15
ajkratos is on a distinguished road
I have 1 idea in mind but not sure if it is correct. So to find velocity fluctuations at a point in the domain...i can turn on the data sampling which will alow me to find average velocity at a specific time and i also have instanteanous velocity at that time, now if i subtract average velocity from the instanteneous velocity am i correct to understand tht i will get fluctuating velocity at tht time at tht point?
ajkratos is offline   Reply With Quote

Old   March 12, 2011, 07:57
Default
  #5
Senior Member
 
xrs333
Join Date: Aug 2010
Posts: 125
Rep Power: 16
xrs333 is on a distinguished road
if you solve n-s eq. like that, you are performing DNS.
non of the turbulent models, including LES, solves for the instantaneous velocity.
xrs333 is offline   Reply With Quote

Old   March 12, 2011, 08:52
Default
  #6
New Member
 
Join Date: Dec 2010
Posts: 13
Rep Power: 15
ajkratos is on a distinguished road
thanks for ur reply. ok i understand wat u mean...but if i want to find mean TKE in LES wat shuld i do n by velocity fluctuations (u', v', w') i meant 'mean' velocity fluctuations. How do i find the fluctuating components of velocity in fluent? sorry if i m bein very confusing, i m confused myself
ajkratos is offline   Reply With Quote

Old   March 12, 2011, 17:24
Default
  #7
Senior Member
 
xrs333
Join Date: Aug 2010
Posts: 125
Rep Power: 16
xrs333 is on a distinguished road
you can use monitor or export during calculation (menu: file -> export -> ...) to collect transient data.
xrs333 is offline   Reply With Quote

Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Jet fan and Tunnel simulation ahlo7 CFX 9 November 13, 2019 05:54
unsteady velocity inlets thecfduser FLUENT 0 November 26, 2009 23:38
how can I speed up unsteady simulation Avinash_Chandra FLUENT 2 November 6, 2009 02:33
simulation of ceiling fan Raj FLUENT 0 October 3, 2008 06:21
Unsteady velocity Vidya Raja FLUENT 10 June 18, 2006 08:14


All times are GMT -4. The time now is 06:26.