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Dimensions of laplacian in PISO loop

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Old   July 1, 2006, 21:47
Default Hello Friends 1. In the pr
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kumar
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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
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Old   July 3, 2006, 06:08
Default Dear Friends Any comments o
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Dear Friends

Any comments on the above. I am really stuck with my work

thanks in advance

kumar
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Old   July 3, 2006, 14:34
Default Dear Friends Any comments o
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Dear Friends

Any comments on the above would be most welcome

thanks

kumar
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