LES mesh requirement

sharif88 · May 22, 2014, 15:00

Hello everybody
I am simulating turbulent flow in an annulus using LES in CFX
the pipe is 8 meter long and in the meshing I used hexahedral mesh along with inflation layers at both walls of the annulus,
in the streamwise direction I have meshes of constant length (5 mm) but much finer mesh in cross sectional area to capture near wall effect.
No as I now LES filter applies based on mesh size I want to know which characteristic length is taken as cut off size between large eddies and smaller one which are not simulated directly.
I thought this length is (V)^(1/3) where V is the volume of each control volume but I am not sure of it.
I appreciate your time in advance

ghorrocks · May 22, 2014, 19:47

Look in a turbulence textbook like "Turbulence Modelling for CFD" by Wilcox for the answer to this.

But be aware that it is not a cut-off (which implies to me a sharp transition). The filter is done by mesh resolution and the cut-off is occurs over a range, more like a low-pass filter.

sharif88 · May 23, 2014, 11:10

Thanks Glenn
I think the filter is a box volume filter which dictates the smallest scale of the resolved eddies and that tells me volume is more important than one characteristic length.

Cheers,

May 22, 2014, 15:00	LES mesh requirement	#1
sharif88 New Member Majid Join Date: Jan 2014 Location: Canada Posts: 23 Rep Power: 13	Hello everybody I am simulating turbulent flow in an annulus using LES in CFX the pipe is 8 meter long and in the meshing I used hexahedral mesh along with inflation layers at both walls of the annulus, in the streamwise direction I have meshes of constant length (5 mm) but much finer mesh in cross sectional area to capture near wall effect. No as I now LES filter applies based on mesh size I want to know which characteristic length is taken as cut off size between large eddies and smaller one which are not simulated directly. I thought this length is (V)^(1/3) where V is the volume of each control volume but I am not sure of it. I appreciate your time in advance

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
sliding mesh problem in CFX	Saima	CFX	46	September 11, 2021 08:38
[snappyHexMesh] No layers in a small gap	bobburnquist	OpenFOAM Meshing & Mesh Conversion	6	August 26, 2015 10:38
Moving mesh	Niklas Wikstrom (Wikstrom)	OpenFOAM Running, Solving & CFD	122	June 15, 2014 07:20
3D Hybrid Mesh Errors	DarrenC	ANSYS Meshing & Geometry	11	August 5, 2013 07:42
[snappyHexMesh] snappyHexMesh won't work - zeros everywhere!	sc298	OpenFOAM Meshing & Mesh Conversion	2	March 27, 2011 22:11

May 22, 2014, 19:47		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,902 Rep Power: 144	Look in a turbulence textbook like "Turbulence Modelling for CFD" by Wilcox for the answer to this. But be aware that it is not a cut-off (which implies to me a sharp transition). The filter is done by mesh resolution and the cut-off is occurs over a range, more like a low-pass filter.

May 23, 2014, 11:10		#3
sharif88 New Member Majid Join Date: Jan 2014 Location: Canada Posts: 23 Rep Power: 13	Thanks Glenn I think the filter is a box volume filter which dictates the smallest scale of the resolved eddies and that tells me volume is more important than one characteristic length. Cheers,