# Mesh in LES

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

 November 8, 2012, 12:07 Mesh in LES #1 Senior Member   Julien Join Date: Jun 2012 Location: France Posts: 152 Rep Power: 7 Hi every Foamers! I have read somewhere (but I can't remember where !!!) that mesh refinement was forbidden in LES, because the filtering operator has to permute with integral and derivative ones, which is possible only if delta is not constant. Does anybody confirm this? I easily admit this. If there is a "large" cell close to a "small" one (let's say half), how to make comunicating the cells concerning the eddies modelled in the large cell and calculated in the small cell !?! Thus, I understand that a mesh has to be uniform. At least changing very smoothly. On the other hand, I can read a lot of papers with refined meshs close to the walls and bluff bodies. How can this be ? Anyone to explain me? hulli likes this.

November 8, 2012, 12:48
#2
Senior Member

Julien
Join Date: Jun 2012
Location: France
Posts: 152
Rep Power: 7
I've got it:
Alberto Passalacqua wrote:
Quote:
 You need good and prett uniform mesh anyways for LES, since you are assuming the filter operator and the differential operator are commutative, which is not true on non-uniform grids!

November 9, 2012, 11:25
#3
Senior Member

Bernhard
Join Date: Sep 2009
Location: Delft
Posts: 790
Rep Power: 15
Quote:
 Originally Posted by Djub On the other hand, I can read a lot of papers with refined meshs close to the walls and bluff bodies. How can this be ?
The point for a good LES simulation, is that you want to resolve 80% of the energy spectrum. Near the wall, you will have more energy in the smaller scales, so you need a fine grid there. Only in LES, you want to have cells with a low aspect ratio (which is not necessary in RANS), so you need to refine them in all three directions. If you apply that refinement globally, the amount of cells will get out of hand quite soon. So it is more a compromise to still perform LES.

Be sure to check out the PhD thesis by Eugene de Villiers, (see http://foamcfd.org/resources/theses.html ), he is addressing some of the issues you mention.

 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 everest ANSYS Meshing & Geometry 44 April 14, 2016 06:41 Soder OpenFOAM 0 June 14, 2011 10:10 SSL FLUENT 2 January 26, 2008 12:55 John Deas FLUENT 2 December 1, 2007 05:56 Jason Main CFD Forum 1 February 10, 2004 17:48

All times are GMT -4. The time now is 11:49.