[su_junwei]

Hi Khaled

From the message above, we can infer that the type of alpha and U are incompatible. for instance, volScalarField + volVectorField

I also noticed that the code segment below
+ fvm::Sp(ix, alpha)
it is a impilit operation, if alpha and U are not the same object, adding them will also cause the problems.

Hope this helps

Junwei

[booz]

Hi Junwei,

thanks for the answer.
For alpha i add

volVectorField alpha
(
IOobject
(
"alpha",
runTime.timeName(),
mesh,
IOobject::MUST_READ,
IOobject::AUTO_WRITE
),
mesh
);

I thought for ix it is enough to be a volScalar or a Scalar.

Khaled