Divergence
 

Could anybody tell me what die fvm::div(phi,U) scheme is doing in OpenFoam?



Is div(-phi,U) the same as -div(phi,U) ?

I suggest having a look at the Programmers Guide (P-38ff).

I read it already, but it does not help me.
According to the Programmers Guide -fvm::div(phi,U) und fvm::div(-phi,U)
should make no difference, but in my case it does.

It depends on what convection scheme you are using. If it is symmetric (linear or harmonic) it shouldn't make a difference. If it is upwind or downwind biased, adding the minus will obviously switch the bias direction to the other cell bordering the face.