Mesh size for turbulence boundary layer

tongx051 · October 20, 2013, 12:07

Hello guys,

I have several questions regarding mesh resolution for turbulence modeling.

1. What’s the mesh resolution required to solve a turbulence boundary layer with RANS?
2. What’s the mesh resolution required to solve a turbulence boundary layer with LES?
3. How does result look like if the mesh resolution is not enough(in Fluent)?
4. If wall function is applied, what the required resolution then? How many grids do I need inside the viscous sublayer and buffer layer? What grid growth rate is recommended?
5. Is the wall function for LES different from the standard wall function for RANS?
6. In LES simulation, what happens if no wall function is applied and near-wall mesh is not fine enough?
7. For modeling flow over several bluff body, there are typically flow separation, adverse pressure gradients, and wake interaction. Is wall function still valid in this case?
8. What’s recommended the mesh resolution for the free shear region (far from the wall) with LES and RANS?

I appreciate your help!

Jeremy

FMDenaro · October 20, 2013, 15:19

too many questions for being answered in a brief post....

just consider that "resolving" the boundary layer means that you have enough points in the range y+ = 0..5. In principle, this is valid fore DNS/LES and often can be a guideline also for RANS.
Wall models must be different for LES and RANS since different is the meaning of the variable resolved.

October 20, 2013, 12:07	Mesh size for turbulence boundary layer	#1
tongx051 New Member Jeremy Join Date: Mar 2011 Posts: 6 Rep Power: 15	Hello guys, I have several questions regarding mesh resolution for turbulence modeling. 1. What’s the mesh resolution required to solve a turbulence boundary layer with RANS? 2. What’s the mesh resolution required to solve a turbulence boundary layer with LES? 3. How does result look like if the mesh resolution is not enough(in Fluent)? 4. If wall function is applied, what the required resolution then? How many grids do I need inside the viscous sublayer and buffer layer? What grid growth rate is recommended? 5. Is the wall function for LES different from the standard wall function for RANS? 6. In LES simulation, what happens if no wall function is applied and near-wall mesh is not fine enough? 7. For modeling flow over several bluff body, there are typically flow separation, adverse pressure gradients, and wake interaction. Is wall function still valid in this case? 8. What’s recommended the mesh resolution for the free shear region (far from the wall) with LES and RANS? I appreciate your help! Jeremy

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
[snappyHexMesh] Number of cells in mesh don't match with size of cellLevel	colinB	OpenFOAM Meshing & Mesh Conversion	14	December 12, 2018 08:07
An error has occurred in cfx5solve:	volo87	CFX	5	June 14, 2013 17:44
Low Mixing time Problem	Mavier	CFX	5	April 29, 2013 00:00
[Gmsh] 2D Mesh Generation Tutorial for GMSH	aeroslacker	OpenFOAM Meshing & Mesh Conversion	12	January 19, 2012 03:52
fluent add additional zones for the mesh file	SSL	FLUENT	2	January 26, 2008 11:55

October 20, 2013, 15:19		#2
FMDenaro Senior Member Filippo Maria Denaro Join Date: Jul 2010 Posts: 6,764 Rep Power: 71	too many questions for being answered in a brief post.... just consider that "resolving" the boundary layer means that you have enough points in the range y+ = 0..5. In principle, this is valid fore DNS/LES and often can be a guideline also for RANS. Wall models must be different for LES and RANS since different is the meaning of the variable resolved.