# calculation of gradients near wall

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 November 5, 2009, 02:51 calculation of gradients near wall #1 New Member   Sumeet Kumar Join Date: Mar 2009 Posts: 21 Rep Power: 10 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

 November 5, 2009, 09:54 #2 New Member   Sumeet Kumar Join Date: Mar 2009 Posts: 21 Rep Power: 10 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( "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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