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

LES energy spectrum

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

Like Tree1Likes
  • 1 Post By MadsR

Reply
 
LinkBack Thread Tools Display Modes
Old   June 16, 2008, 16:18
Default LES energy spectrum
  #1
Hummi
Guest
 
Posts: n/a
Hi Guys

I want to plot energy spectrum (temporal spectrum) for my LES simulation. Can you guys please explain how can i do that. I have matlab and mathcad. If some one has a code for it and can pass it on to me, it will very helpful. Thank you so much.

  Reply With Quote

Old   June 16, 2008, 21:41
Default Re: LES energy spectrum
  #2
Glenn Horrocks
Guest
 
Posts: n/a
Hi,

Put a monitor point in your domain and record the U, V, W velocities (or any other turbulence parameter which you wish to get the spectrum from, maybe pressure, temperature, species etc). Do an FFT on it. Draw spectrum.

Glenn Horrocks
  Reply With Quote

Old   June 17, 2008, 05:15
Default Re: LES energy spectrum
  #3
Hummi
Guest
 
Posts: n/a
Thank you Glenn. Which velocities should I monitor, instantaneous or mean? How do I do FFT, can you please expand on that. Thanks

Hummi
  Reply With Quote

Old   June 18, 2008, 16:10
Default Re: LES energy spectrum
  #4
Hummi
Guest
 
Posts: n/a
I know how to do FFT on it velocities. How do I do last bit i.e. draw spectrum.

Hummi
  Reply With Quote

Old   February 12, 2010, 08:21
Default
  #5
New Member
 
Ali
Join Date: Jul 2009
Posts: 1
Rep Power: 0
eng1182 is on a distinguished road
hi Hummi

energy spectrum is a type of transient results representation which only needs any variable as a function of time and transform it to the strength of this variable as a function of frequency. so it dose not depend on a specified variable the variable can be any variable like velocity, pressure or temperature
eng1182 is offline   Reply With Quote

Old   February 15, 2010, 04:53
Default
  #6
Senior Member
 
MadsR's Avatar
 
Mads Reck
Join Date: Aug 2009
Location: Copenhagen, Denmark
Posts: 175
Rep Power: 8
MadsR is on a distinguished road
Often, it would be interesting to show a separate energy spectrum from samplings of u, v, and w. But, you could show an energy spectrum for the resulting velocity (i.e. the speed) only. It depends on your case really.
If you want to show/look for turbulent coherent structures in the flow, velocities would be a good choice. Pressure would also reflect this, but obviously you loose the directional information seen in separate spectra of u,v,w.
One could also make a spectrum of the lift/drag forces on an airfoil to try to investigate phenomena related to the surface flow. Possibilities are infinite :-)

Hope it helps you a bit.

Oh, and remember to sample at at least twice the rate as you want to resolve in your spectrum and also to get "sufficiently" long time-series. If you can see some periodicity in the velocities, for instance, be sure to get, say, at least 20 of those cycles. Again, this depends heavily on the flow at hand, and needs your engineering judgement :-) all kinds of weird stuff can happen when sampling a signal, consult text books or Google on this :-)

/Mads
solefire likes this.
__________________
Online free airfoil-mesher for OpenFOAM here
MadsR 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
LES: Energy spectrum Hummi NUMECA 0 June 16, 2008 16:21
LES: Energy spectrum Hummi Main CFD Forum 0 June 16, 2008 16:19
Energy spectrum LES Hummi Phoenics 0 June 16, 2008 16:18
Energy spectrum LES Hummi CD-adapco 0 June 16, 2008 16:17
LES correlation and turbulent energy spectrum Fabian Main CFD Forum 4 October 18, 2005 02:04


All times are GMT -4. The time now is 23:59.