# How to make grid for LES simulation

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 November 9, 2015, 22:32 How to make grid for LES simulation #1 Member   Anh Join Date: Sep 2014 Posts: 69 Rep Power: 11 Hello, I am trying to do simulation with the LES model for the nozzle flow. For LES, that requires a large of number of grid. However, if I understand correctly, there is no rule for the number of grid for LES where the turbulent length scale is compared to the local grid size. it means that the domain grid is depended on how detail of turbulent effect you want to know, doesn't it? I read in some papers, the number of grid for LES is listed as Nx, Ny, Nz. What are those number? In case I make the grid for Fluent, how small of cell, and how many cells I need to make? In case using wall function for LES (in Fluent), the first grid cell should be in the log law region, shouldn't it? Thank you.

November 10, 2015, 04:35
#2
Senior Member

Filippo Maria Denaro
Join Date: Jul 2010
Posts: 6,793
Rep Power: 71
Quote:
 Originally Posted by dinhanh Hello, I am trying to do simulation with the LES model for the nozzle flow. For LES, that requires a large of number of grid. However, if I understand correctly, there is no rule for the number of grid for LES where the turbulent length scale is compared to the local grid size. it means that the domain grid is depended on how detail of turbulent effect you want to know, doesn't it? I read in some papers, the number of grid for LES is listed as Nx, Ny, Nz. What are those number? In case I make the grid for Fluent, how small of cell, and how many cells I need to make? In case using wall function for LES (in Fluent), the first grid cell should be in the log law region, shouldn't it? Thank you.

- Nx, Ny, Nz are the numbers of cells in x, y and z directions, respectively
- using wall function (direction y normal to wall) you can use the first cell at larger y+
- using a grid resolving the BL, requires to have at least 3-4 nodes within y+<1
- if x, z are directions of homeneity for the flow, you can use a grid such that dx+ and dz+ are of O(20)-O(30)

November 10, 2015, 21:07
#3
Member

Anh
Join Date: Sep 2014
Posts: 69
Rep Power: 11
Quote:
 Originally Posted by FMDenaro - Nx, Ny, Nz are the numbers of cells in x, y and z directions, respectively - using wall function (direction y normal to wall) you can use the first cell at larger y+ - using a grid resolving the BL, requires to have at least 3-4 nodes within y+<1 - if x, z are directions of homeneity for the flow, you can use a grid such that dx+ and dz+ are of O(20)-O(30)
Thank you, FMDenaro,

you mean Nx, Ny, Nz are the numbers of cells in x, y and z direction for the whole domain?

What do you mean "homeneity for the flow"?

Do you have an example of the grid of the simple domain for LES modelling?

 November 11, 2015, 02:37 #4 Senior Member   Filippo Maria Denaro Join Date: Jul 2010 Posts: 6,793 Rep Power: 71 "homogeneity" ... see here https://www.researchgate.net/publica...ates_revisited