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-   -   calculation of gradients near wall (http://www.cfd-online.com/Forums/openfoam/69794-calculation-gradients-near-wall.html)

crazysumi November 5, 2009 02:51

calculation of gradients near wall
 
Hi FOAMers,

I want to calculate gradients at the cell centroids connected to a wall patch.

The quantities I need to evaluate are :-
a) del Utau / del tau
b) del Unormal / del normal
c) del p / del tau

Here,
Utau is tangential component of velocity
Unormal is normal component of velocity
tau is a coordinate tangent to local wall face
normal is a coordinate normal to local wall face

Can someone assist me calculation of these quantities at the cell centroids. Hints and suggestions in this regard are greatly appreciated

Thanks & Regards
Sumeet

crazysumi November 5, 2009 09:54

Hi Again

I tried to calculate following quanitity..

1) del p / del tau
vectorField n = patch().nf() / mag( patch().nf() ) ;
volVectorField gradP(fvc::grad(db().lookupObject<volScalarField>( "p")));
const vectorField gradPInternal = gradP.boundaryField()[patchI].patchInternalField();
const scalarField gradPtau = mag(gradPInternal - n * (gradPInternal & n));

The scalarField gradPtau will give me the required derivative

However the above method cannot be reiterated for calculation of following derivatives.-
a) del U(tau) / del tau
b) del U(normal) / del normal

because the U (tau) and U (normal) vectors are only defined at the cell centroids of patchInternalField list. How do I calculate such derivatives. Please someone advice.

Regards,
Sumeet


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