# Dimensions of laplacian in PISO loop

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 July 1, 2006, 21:47 Hello Friends 1. In the pr #1 Senior Member   kumar Join Date: Mar 2009 Posts: 112 Rep Power: 8 Hello Friends 1. In the present PISO loop in say interFoam we have laplacian(rUAf,pd)=div(phi) say , eqn A both rUAf , phi are evaluated at the cell face. dimension of rUAf = (m^3 . S)/kg dimension of phi = m^3/S dimension of pd = kg/(m.S^2) since pd is at the cell centre . i found the laplacian of (rUAf,pd) as div( rUAf*|S|*grad(p)_face ) which equals div( [m^3 .S /kg] * [m^2] * [kg/(m.S^2)]*[1/m]) and this works out to be div ( m^3 / S ) . which equals the RHS eqn A. first question is IS THIS CORRECT ?? 2. when i multiply both sides with density as shown in eqn B below why is it dimensionally incompatible ? phi=phi*rhof rhof is the density at the face of cell with dimensions [kg/m^3 ] rUAf_rhof = rUAf*rhof laplacian( rUAf_rhof , pd)=div(phi) equation (B) . But now OpenFOAM gives the following error --> FOAM FATAL ERROR : Different dimensions for = dimensions : [0 3 -1 0 0 0 0] = [1 0 -1 0 0 0 0] From function dimensionSet::operator=(const dimensionSet& ds) const in file dimensionSet/dimensionSet.C at line 158. FOAM aborting This is really strange. phi has changed its dimensions on expected lines , BUT NOT the LHS of eqn B . thanks in advance. Kumar

 July 3, 2006, 06:08 Dear Friends Any comments o #2 Senior Member   kumar Join Date: Mar 2009 Posts: 112 Rep Power: 8 Dear Friends Any comments on the above. I am really stuck with my work thanks in advance kumar

 July 3, 2006, 14:34 Dear Friends Any comments o #3 Senior Member   kumar Join Date: Mar 2009 Posts: 112 Rep Power: 8 Dear Friends Any comments on the above would be most welcome thanks kumar

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