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

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

 March 9, 2012, 00:13 how to get the turbulence intensities, length scales, draw power spectra? #1 New Member   Join Date: Mar 2012 Posts: 4 Rep Power: 7 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,

 March 9, 2012, 05:12 #2 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 14,088 Rep Power: 109 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.

March 9, 2012, 11:33
#3
New Member

Join Date: Mar 2012
Posts: 4
Rep Power: 7
Quote:
 Originally Posted by ghorrocks 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

 March 10, 2012, 05:44 #4 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 14,088 Rep Power: 109 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.

 Thread Tools Display Modes Linear Mode

 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 OffTrackbacks are On Pingbacks are On Refbacks are On Forum Rules

 Similar Threads Thread Thread Starter Forum Replies Last Post Wen Long Main CFD Forum 3 May 15, 2009 09:52 bajjal Main CFD Forum 9 May 24, 2006 02:19 bf Main CFD Forum 1 April 13, 2006 01:55 lei Main CFD Forum 0 September 26, 2002 04:07 Anne-Marie Giroux Main CFD Forum 3 July 5, 1999 21:28

All times are GMT -4. The time now is 03:32.