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Harry October 3, 2006 23:04

Gradient calculation
To calculate 3-D gradient at centroid of a cell, which neighboring cells should be involved? To explain my question in clarity , I divide the neighboring cells of the considered cell into two groups. one group is the cell which has a common face with the considered cell. one group is the cell which only has a common line/point with the cosidered cell. Should I include both two group for gradiet calculation, Or the first group is enough. I found my code based on unstructured grids just considered the neigbouring cells with common face. Now I want to use gradient for interpolation of value at a arbitry point in a cell. I doubt the existing method of gradient calculation is not good enough.

I would appreciate your idea.



Sunny October 7, 2006 03:02

Re: Gradient calculation
Hi Harry,

I have used the first group for gradient calculation, that is only the neighbors with will my cell shares common faces. Using this gradient value for interpolation, I was able to obtain good results for unstructured grids.

I dont think the value of the gradient should depend on values of cells with common edges or vertices, as you dont have any flux input through these cells.


Sunny October 7, 2006 03:07

Re: Gradient calculation (typo)
....only the neighbors with WHICH my cell shares common faces....

Harry October 7, 2006 04:19

Re: Gradient calculation (typo)
Thanks, Sunny. I orginally want to acquire gas properties (velocity, porosity, pressure) at an arbitary point in a cell using their gradients. I mean gradient is used for interpolation calculation, not for the solution of fluid flow.

The related results are dissapoint as this method has a bad boundedness (some value is beyong physical meaning) and accuracy, especially for big-size cell.

Now I completely give it up.

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