CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > CFX

how to get the turbulence intensities, length scales, draw power spectra?

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

Reply
 
LinkBack Thread Tools Display Modes
Old   March 9, 2012, 00:13
Default how to get the turbulence intensities, length scales, draw power spectra?
  #1
New Member
 
Join Date: Mar 2012
Posts: 2
Rep Power: 0
Stan_Mech is on a distinguished road
Hello everyone,

how can I plot the turbulence intensity along a line, length scales and time scales and power spectra at certain location?

also anybody knows about turbulent production, how can i plot these too along a line?

Thanks,
Stan_Mech is offline   Reply With Quote

Old   March 9, 2012, 05:12
Default
  #2
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 10,831
Rep Power: 85
ghorrocks has a spectacular aura aboutghorrocks has a spectacular aura aboutghorrocks has a spectacular aura about
Turbulence intensity - easy, just plot k along a line feature.
Length/time scales - you will have to define a variable for your length/time scale, but that is easy to plot along a line feature.
Turb production - again define a variable which describes this and plot it.

The above ones you can do in a 2 eqn turbulence model This next one requires an LES style model:

Power spectra - To do this you need to use transient statistics, but to do a proper spectra you will need to use a monitor point and export the data and do post-processing elsewhere.
ghorrocks is offline   Reply With Quote

Old   March 9, 2012, 11:33
Default
  #3
New Member
 
Join Date: Mar 2012
Posts: 2
Rep Power: 0
Stan_Mech is on a distinguished road
Quote:
Originally Posted by ghorrocks View Post
Turbulence intensity - easy, just plot k along a line feature.
Length/time scales - you will have to define a variable for your length/time scale, but that is easy to plot along a line feature.
Turb production - again define a variable which describes this and plot it.

The above ones you can do in a 2 eqn turbulence model This next one requires an LES style model:

Power spectra - To do this you need to use transient statistics, but to do a proper spectra you will need to use a monitor point and export the data and do post-processing elsewhere.
thanks,

Thanks,

would K be representative of turbulence intensity? or should i process it because k=0.5(3*u^2) (assuming its isentropic) but the intensity is u/U_mean

for defining a variable for the length scales you mean from statistics equation, what would be the variable, where can i place it?

for the power spectra, why specially LES? ,can I use other models like SST or k epsilon
Stan_Mech is offline   Reply With Quote

Old   March 10, 2012, 05:44
Default
  #4
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 10,831
Rep Power: 85
ghorrocks has a spectacular aura aboutghorrocks has a spectacular aura aboutghorrocks has a spectacular aura about
Sorry, I misunderstood your initial question. People often refer to k as turbulence intensity. But if you are looking for % turbulence intensity then define a variable and plot that. Still very easy.

k is directly linked to turbulence intensity.

In a 2 eqn turbulence model if you have two turbulence parameters (say k and epsilon) then you can derive all other turbulence parameters such as length scales from that. You just need to know how they are related. "Turbulence Modelling for CFD" by Wilcox is a good one and has all the relationships.

2 eqn turbulence models assume a single length and time scale represents the turbulence at that location. You cannot get a spectrum from that.
ghorrocks is offline   Reply With Quote

Reply

Thread Tools
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 On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Discussion: Reason of Turbulence!! Wen Long Main CFD Forum 3 May 15, 2009 09:52
length scales in turbulence bajjal Main CFD Forum 9 May 24, 2006 02:19
how does the wake length depend on turbulence bf Main CFD Forum 1 April 13, 2006 01:55
Turbulence length scale in pipe flow lei Main CFD Forum 0 September 26, 2002 04:07
length scales at inlet for internal flows Anne-Marie Giroux Main CFD Forum 3 July 5, 1999 21:28


All times are GMT -4. The time now is 02:10.