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-   -   What is meant by Grid Independence Study? (http://www.cfd-online.com/Forums/fluent/40902-what-meant-grid-independence-study.html)

Khan May 10, 2006 04:46

What is meant by Grid Independence Study?
 
Hi

I am trying to model flow over an airfoil with Mach 0.1. Can any person help me in

a. What is meant by Grid independent Study? b. Can 2-D grid independent study be applied over 3-D?

Urgent help is requested.

Cheers


FarhathAlam May 10, 2006 05:51

Re: What is meant by Grid Independence Study?
 
Hi, The coarse mesh which gives a solution which is invariant with the finer meshes . In your case ,if you have carried out analysis for an aerofoil with one particular mesh size and solution doesnt change if the same is carried for caorser mesh .the grid independence is said to be achieved. the coarse mesh is used for further analysis.


manoj korde May 10, 2006 07:50

Re: What is meant by Grid Independence Study?
 
when u solve any cfd problem the solution should be should not be affected by the size of ur grid. Grid independence is done to ensure that ur solution is indendent on the grid size.we try to solve same problem with fine grid and see the variation in result .

Khan May 11, 2006 06:04

Re: What is meant by Grid Independence Study?
 
Thanx for the response. So it means that grid independence study is for specific turbulence model and can't be applied across the models? Also can 2D airfoil grid independent study be applied for 3D wing?


FarhathAlam May 11, 2006 06:08

Re: What is meant by Grid Independence Study?
 
No,it has to done seperately

sam May 11, 2006 07:15

Re: What is meant by Grid Independence Study?
 
are u sure. that grid independece study is repeated for eachturbulence model

Farhath May 11, 2006 07:43

Re: What is meant by Grid Independence Study?
 
grid independence study need not be carried for each turbulence model .it has to be carried seperately for the 3D grid.

Khan May 11, 2006 10:41

Re: What is meant by Grid Independence Study?
 
I am confused. Does this means that for K-E and SA models, the grid will be different because i did 2D airfoil case on K-E model and got results with reasonable fine results which were varying less than 1% as we go towards finer grid. But once i applied same mesh to SA or K-W, i gave me different results.

So does grid indepence study really means " Single grid for turbulence models" or "Single grid for single turbulence model"?


Riaan May 11, 2006 13:22

Re: What is meant by Grid Independence Study?
 
GRID dependency, not TURBULENCE model dependency. As you refine the grid, and you change your y+ values, make sure that your y+ values are still in an acceptable range for the various turbulence models.

Typically, for external aerodynamics, I will refine the grid until the solution does not change, then check the effect of turbulence models for that fine grid (assuming y+ is always in valid range)

roddyalan November 5, 2009 10:35

Hi guys, dumb question, what do you mean by solution. Does it mean residuals become constant.

Mahmudrochy July 2, 2015 22:40

It means any of the output parameters, such as velocity, turbulent KE, skin friction coefficient etc....


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