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 Chris Lucas January 20, 2011 10:08

get velocity gradient with a boundary function

Hi
I want to write a new inlet boundary condition for epsilon. For this new boundary condition, I need calculate for instance the velocity gradient ( and magSqr(symm(fvc::grad(U))) )

I know I can get the velocity field at the patch using:
const fvPatchField<vector>& U = patch().lookupPatchField<volVectorField, vector>("U");

The problem is (as I understand it) that by using the code above, U is a “vector patch field”. But if I want to get the velocity gradient (using fvc::grad(U)), U must be a volVectorField.

Is there a way to get the velocity of the entire grid within the boundary condition, so that I can calculate the velocity gradient and then use this result to get the velocity gradient at the patch?

Thanks for the help.
Christian

 lindstroem August 10, 2011 05:57

Hi Chris,

did you succeed?

I also want to get the velocity gradient at a patch..

 Chris Lucas August 10, 2011 08:36

Hi,

I didn't looked into this subject much more and therefore didn't solve the problem. Please let me know if you do :)

Best Regards
Christian

 mathslw August 24, 2012 13:17

Quote:
 Originally Posted by lindstroem (Post 319598) Hi Chris, did you succeed? I also want to get the velocity gradient at a patch.. Thanks in advance.
Hi,

I also want to get the velocity gradient at a patch.

did you succeed?

Thanks!

Wei

 Chris Lucas August 27, 2012 03:11

Hi,

no, I have not continued this work.

The following is a guess only (not sure if this works or even if this is correct):

I guess you need the normal BC gradient and not the fvc::grad.