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

Length scale separation in LES

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

Reply
 
LinkBack Thread Tools Display Modes
Old   June 7, 2002, 07:01
Default Length scale separation in LES
  #1
Ray
Guest
 
Posts: n/a
Hi, All,

Can anybody suggest how to determine or ensure length scale separation in LES? or how to ensure my cut-off length scale is inside the inertial subrange of the turbulent energy spectrum?

My case is that I have a package to run LES for an oscillatory flow. Apparently, the package runs well and I have got some results.I can change/refine my mesh, but do not know if this helps. I need to justify my application of LES for such a flow. As known, LES is usually valid for high Reynolds number flow where length scale separation presents. But for an oscillatory flow, the Reynolds number seems different from a pipe flow or free stream,...

Many thanks!
  Reply With Quote

Old   June 7, 2002, 08:50
Default Re: Length scale separation in LES
  #2
Jonas Larsson
Guest
 
Posts: n/a
What is your Re number?

One check you can do is to perform an FFT (Fast Fourier Transform) of your solution. Plot the energy spectrum and make sure that you don't have any accumulation of energy at the smallest scales (your grid size). If you have an energy peak at the size of your grid then you are not resolving enough.

Be careful though, many sub-grid models (Smagorinsky for example), are often too dissipative and can hide these problems.
  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
Integral Length Scale vs Turbulent Length Scale Scott Nordsen FLUENT 2 January 20, 2014 02:17
integral length scale and cross-correlation (with openfoam data, LES pipe flow) jet Main CFD Forum 0 June 4, 2010 08:07
Turbulence length scale and integral length scale rizhang CFX 1 September 10, 2009 06:38
LES inlet length scale f.neilson Main CFD Forum 0 January 31, 2005 14:26


All times are GMT -4. The time now is 14:39.