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How to make grid for LES simulation

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Old   November 9, 2015, 22:32
Post How to make grid for LES simulation
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Anh
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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.
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Old   November 10, 2015, 04:35
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Quote:
Originally Posted by dinhanh View Post
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)
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Old   November 10, 2015, 21:07
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Originally Posted by FMDenaro View Post
- 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?
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Old   November 11, 2015, 02:37
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"homogeneity" ...

see here https://www.researchgate.net/publica...ates_revisited
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