Hi to everybody! I'm writing
 

Hi to everybody!
I'm writing a solver for the linearized euler eq., and I have some problems in the momentum eq.

du'/dt + Ma & grad(u') + u' div(Ma) = -grad(p')

where u', Ma are volVectorField
The problem is in Ma & grad(u'), I can only discretize it like Ma & fvc::grad(u), with u volVectorField. If I try to calculate the face flux of u',

surfaceScalarField phiU1 = fvc::interpolate(u1)&mesh.Sf();

and put them in grad(phiU1) I have errors.
I tryied to look up and down for examples, but I can't find anything similar.
What's wrong in my code?
Thank you in advance!