CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Software User Forums > OpenFOAM > OpenFOAM Verification & Validation

Grid Independence Study, how to start?

Register Blogs Members List Search Today's Posts Mark Forums Read

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   August 28, 2021, 06:53
Default Grid Independence Study, how to start?
  #1
Member
 
Claudia
Join Date: Mar 2021
Posts: 43
Rep Power: 5
Clau.77 is on a distinguished road
Hey guys,


for my steadyState multiRegion case I would like to perform a grid convergence study. The case is a flow around an object.


I have never done that before, so I am a bit confused on how to start. I was thinking about first doing a coarse grid and then two finer grids. The question is: what about adding layers near the wall?
Am I first doing a study without any layers, find the best mesh and then do another study to find the right amount of layers??
Clau.77 is offline   Reply With Quote

Old   August 30, 2021, 06:49
Default
  #2
Senior Member
 
Join Date: Apr 2020
Location: UK
Posts: 674
Rep Power: 14
Tobermory will become famous soon enough
You are right to be cautious here - essentially you have two different grid effects that you are discussing here:
1. Wall resolution of the boundary layer(s); this is dependent primarily on the cell y+ values, but also potentially their shape (are you running RANS, LES, ... ?).
2. Grid resolution of the flow (and scalar) gradients in the main body of the flow.

The nature of your test case (aerofoil flow? bluff body separation? mixing vessel? etc etc) will determine the relative importance of the above two effects. Have a think about what is dominant in your flow, and make sure you test these independently (eg keep wall y+ fixed while you vary the mesh size in the interior of the flow, or vice versa), since otherwise it will get very confusing for you. Good luck!
Tobermory is offline   Reply With Quote

Old   May 3, 2024, 12:34
Default
  #3
New Member
 
mo magd
Join Date: Apr 2024
Posts: 7
Rep Power: 2
mo___ is on a distinguished road
Hi Tobermory,



I'm trying to perform a grid independence test on turbulence modeling for my problem, which involves the mixing process in a micromixer through LES simulation using OpenFOAM.
In a laminar case, I could easily refine the background mesh by choosing smaller values for dx, dy, and dz to obtain a finer mesh and conduct the grid test analysis straightforwardly. However, since my simulation involves turbulence modeling through LES, I am unsure how to proceed. My geometry is quite complex and not symmetrical, adding to the challenge. I'm also uncertain about the necessary steps for conducting a decent grid test analysis for LES simulation in OpenFOAM.
I would highly appreciate your assistance. If anyone knows of a good resource such as a video tutorial or thesis on this topic, it would be greatly beneficial.
Thank you all so much for your help.
mo___ is offline   Reply With Quote

Old   May 7, 2024, 04:14
Default
  #4
Senior Member
 
Join Date: Apr 2020
Location: UK
Posts: 674
Rep Power: 14
Tobermory will become famous soon enough
Grid sensitivity studies are indeed more complex for LES studies since changing the grid size also changes the time step and therefore temporal and frequency resolution, and also the magnitude of the resolved scales and the balance between resolved/SGS energy. Be careful with the latter to ensure that you still maintain adequate/suitable conditions for LES.

I don't have any examples of previous LES grid refinement studies - apologies & good luck.
Tobermory is offline   Reply With Quote

Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
[ANSYS Meshing] How to: Grid independence study for structured mesh Dronzer ANSYS Meshing & Geometry 8 March 31, 2018 23:37
[ICEM] Mesh Independence study Carlos Modesto ANSYS Meshing & Geometry 4 July 7, 2017 06:57
Grid independence study problem Bisht STAR-CCM+ 8 February 2, 2016 13:28
Grid Independence of Boundary layer Luigi_ Main CFD Forum 0 December 14, 2011 13:42
A doubt on grid independence study G.Balakrishnan FLUENT 4 November 21, 2000 11:05


All times are GMT -4. The time now is 16:43.