|October 7, 2007, 09:50||
How to mesh the 1st grid point
Daniel WEI (老魏)
Join Date: Mar 2009
Location: Beijing, China
Blog Entries: 9Rep Power: 13
How to mesh the 1st grid point?
I am very young to CFD world. I'm trying to use oodles to learn LES techniques.
Now I have some problems about meshing.
I saw a paper on flow over a cylinder using Fluent, its meshing guideline is like this,
Reynolds Number | Flow Regime | Yplus/First Cell Height
Re < 1000 | Laminar | First Cell Height = Cylinder Radius/24
1000 < Re < 20000 | Turbulent, Enhanced Wall Treatment | Yplus < 10
Re > 20000 | Turbulent, Standard Wall Functions | Yplus > 30
Why mesh like this? Is there any references on how-to mesh under LES and DNS?
Sorry, I did not find help from <grid> and <fluent>...
Is that mean:
If I use wall function, then I can set the 1st grid point at the place of y+=30?
If I use not wall function, then I should set the 1st grid point at the place of y+=1?
I heard "Laminar LES"=DNS, what does it mean? Is it mean that their mesh is identical?
I see that the 1st grid point is decided by the flow state, but When I predict flow around a building on a certain Re for example, the laminar and turbulence coexist around the building, then how to decide the 1st grid point?
Thanks for your time
Boeing Research & Technology - China
|October 8, 2007, 07:13||
Hey Daniel, I am new to LES
Join Date: Mar 2009
Posts: 48Rep Power: 9
I am new to LES too, and i am running channel flows, what i can tell you is that in LES you have two calculation strategies:
-A direct near wall resolution, the first point grid should lay in the viscous sublayer (y+<5, at least 3 points needed)
-Using wall functions to resolve wall region, with the 1st point grid at the limit of the log region(y+=30).
So your mesh will depend on the calculation strategy you choose.
Hope this helps.
|Thread||Thread Starter||Forum||Replies||Last Post|
|How to mesh the 1st grid point?||Daniel||Main CFD Forum||1||October 8, 2007 02:27|
|udf to set vel. = 0 at a grid point or a cell||Ralf Schmidt||FLUENT||0||September 22, 2006 09:45|
|Estimation of First Grid Point Near Wall||Amer Mahmood||FLUENT||2||April 25, 2006 11:49|
|Estimation of First Grid Point Near Wall||Amer Mahmood||FLUENT||0||April 24, 2006 13:00|
|distance from the wall to the first grid point||Wenqing Zhang||CFX||0||August 9, 2004 10:08|