[Zanco]

Hi everybody.

For some technical and boring reasons, I have to write down the UEqn in a single fvMatrix for the rhoSimpleFoam solver.

I cannot understand why if I create the UEqn as
Ueqn_global.reset(new fvVectorMatrix(getNLTerm(U)
+ getViscTerm(U)
==
fvOptions(rho, U)
));

and in the end solve it like

uresidual_v = solve(UEqn == -fvc::grad(p)).initialResidual()

everything works fine while in case I construct the UEqn as

Ueqn_global.reset(new fvVectorMatrix(getNLTerm(U)
+ getViscTerm(U)
==
fvOptions(rho, U)
));
Ueqn_global().relax();
fvOptions.constrain(Ueqn_global());

Ueqn_global.reset(new fvVectorMatrix(Ueqn_global()
==
-grad(p)
));

and in the end solve it like

uresidual_v = Ueqn_global().solve().initialResidual();

the convergence cannot be reached and it starts oscillating without stopping anymone.
Can anyone help me please?
Thank you in advance.