# How to mesh the 1st grid point

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 October 7, 2007, 09:50 How to mesh the 1st grid point #1 Senior Member     Daniel WEI (老魏) Join Date: Mar 2009 Location: South Bend, IN, USA Posts: 688 Blog Entries: 9 Rep Power: 12 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 Q-1. Why mesh like this? Is there any references on how-to mesh under LES and DNS? Sorry, I did not find help from and ... Q-2. 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? Q-3. I heard "Laminar LES"=DNS, what does it mean? Is it mean that their mesh is identical? Q-4. 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 Daniel __________________ ~ Daniel WEI ------------- NatHaz Modeling Laboratory Department of Civil & Environmental Engineering & Earth Sciences University of Notre Dame, USA Email || My Personal CFD Blog

 October 8, 2007, 07:13 Hey Daniel, I am new to LES #2 Member   hadi tartoussi Join Date: Mar 2009 Location: paris Posts: 48 Rep Power: 8 Hey Daniel, 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. good luck! Hadi

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