How to evaluate a surfaceScalarField face by face?
 

rhoPhi is defined as

surfaceScalarField rhoPhi
(
IOobject
(
"rhoPhi",
runTime.timeName(),
mesh
),
dimensionedScalar("0",dimensionSet(1,0,-1,0,0),0)
);

and it is updated after alphaEqn solved.

Now I want to create a new surfaceScalarField rhoPhi2 ,which is a function of rhoPhi, so I define

surfaceScalarField rhoPhi2
(
IOobject
(
"rhoPhi2",
runTime.timeName(),
mesh
),
dimensionedScalar("0",dimensionSet(1,0,-1,0,0),0)
);

and evaluate rhoPhi2 face by face :

forAll (rhoPhi2 , facei)
{
rhoPhi2[facei] = rhoPhi[facei];
}

but it doesn't work as same as

rhoPhi2 = rhoPhi;

Is there any mistake in my testing code? And How to evaluate a surfaceScalarField face by face?

Thanks!

Have a look at what operator= does for fields in GeometricField.C

You need to also loop over boundaries. I would question why you need to loop though.