Characteristic mesh size in DDES simulation

mattia_samiolo · May 27, 2021, 01:44

Good morning everyone,

I would want your opinion to build the correct mesh around a car, in my case I will use a k-omega SST DDES. I am aware that the measure of the mesh in the boundary condition has to start with a y+ value around 1 because of the SST model, but my concerns arise when the code switch to LES. What calculations or mind path do you use to estimate the mesh in the free stream?

As suggested by (Howard and Pourquie), the recommended mesh size in the detached flow regions for a DES-type simulation should be close to the Taylor microscale given by λ = 15^(1/2) A^( -1/2) Re^(-1/2)L, where A is an undetermined constant set to be 0.5 in this paper, L is the bulk integral scale (taken as the vehicle length, L), and Re the Reynolds number

Howard and Pourquie paper:
https://www.researchgate.net/publica...eference_model

Thank you

airwarriorg91 · April 22, 2025, 10:31

Hello !
The post might be late but I have added a few resources along with your reference which is quite helpful in case of DDES simulations.

1. The reference you mentioned is quite helpful in creating a good mesh and makes sense. There are few other methods to determine the value of Taylor Microscale. I did a RANS and used the results to calculate the Kolmogorov and Taylor length scale.

2. Young Person's guide to grid sizing for DES. Explains the meshing requirements in different zones and helps reduce the mesh size in overall.

3. Guidelines by Molina et. al in the SU2 conference (https://su2foundation.org/wp-content.../06/Molina.pdf)

The guidelines given in the 3rd reference agree quite well with the idea of creating the grid size based on Taylor microscale.

Hope this helps others !

Regards
G

May 27, 2021, 01:44	Characteristic mesh size in DDES simulation	#1
mattia_samiolo New Member Mattia Samiolo Join Date: May 2021 Posts: 2 Rep Power: 0	Good morning everyone, I would want your opinion to build the correct mesh around a car, in my case I will use a k-omega SST DDES. I am aware that the measure of the mesh in the boundary condition has to start with a y+ value around 1 because of the SST model, but my concerns arise when the code switch to LES. What calculations or mind path do you use to estimate the mesh in the free stream? As suggested by (Howard and Pourquie), the recommended mesh size in the detached flow regions for a DES-type simulation should be close to the Taylor microscale given by λ = 15^(1/2) A^( -1/2) Re^(-1/2)L, where A is an undetermined constant set to be 0.5 in this paper, L is the bulk integral scale (taken as the vehicle length, L), and Re the Reynolds number Howard and Pourquie paper: https://www.researchgate.net/publica...eference_model Thank you

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April 22, 2025, 10:31		#2
airwarriorg91 Member Gaurav Gupta Join Date: May 2024 Location: India Posts: 40 Rep Power: 2	Hello ! The post might be late but I have added a few resources along with your reference which is quite helpful in case of DDES simulations. 1. The reference you mentioned is quite helpful in creating a good mesh and makes sense. There are few other methods to determine the value of Taylor Microscale. I did a RANS and used the results to calculate the Kolmogorov and Taylor length scale. 2. Young Person's guide to grid sizing for DES. Explains the meshing requirements in different zones and helps reduce the mesh size in overall. 3. Guidelines by Molina et. al in the SU2 conference (https://su2foundation.org/wp-content.../06/Molina.pdf) The guidelines given in the 3rd reference agree quite well with the idea of creating the grid size based on Taylor microscale. Hope this helps others ! Regards G