[nimasam]

hi friend
i get some how confused about the function of fvc::div in openFoam
how does it work?
i had a scalar variable with dimension set [1 -2 -1 0 0 0 0] after div ,i had
a variable with dimension set [1 -5 -1 0 0 0 0] , how is it possible ?

[idrama]

Basically, div(U):=u_x + v_y + w_z for any tridimensional vector U=[u v w] and div(f):=f_x+f_y+f_z for any scalar field f. Derivation of any quantity includes a change in dimension, for instance, let U be a velocity vector, i.e. [m/s], then U_x has the dimension [1/s]. Better is you would look into book of contiuums mechanics.
Futhermore, in OpenFOAM the evalutaion is numerically, meaning central differencing is used when in fvSchemes
div(U) Gauss linear; is specified. The rest will ya proberly find in some numerical textbooks.

[nimasam]

then what was the reason?
i know the meaning of div(F) i can't understand why initial dimensionSet [1 -2 1 0 ...] after "div" change into [1 -5 1 0 ....] instead of [1 -3 1 0 ...] ?