UEqn without pressure term
Hello,
I have a momentum transport equation which is not pressuredriven, in addition to the continuity equation. Instead it has gravity and drag terms as the driving force. I can include it into OpenFOAM as: div(phi,U) == gravity + drag However, I can not include the continuity equation with this one. The solver does not compile when I try fvm::div(phi) or fvc::div(phi) I know that in simple algorithm, the continuity equation is included in the pressure equation. But i don't have to solve for pressure, it is not anywhere in the equations. How can I do it? 
1 Attachment(s)
I need to include the equation shown in attachment, which is a mass conservation equation, where "a" is phase volume fraction in a multiphase flow.
I defined "a" as a volScalarField. When I do at as: Code:
fvScalarMatrix alphaEqn error: no matching function for call to ‘div(Foam::volScalarField&, Foam::volVectorField&)’ I suppose, I can not use two volume fields as argument in fvm::div Then I switch to Code:
fvScalarMatrix alphaEqn This time solver converges, but when I solve my case, it gives floating point exception if my internal field value for "a" is different than the voundary condition value. 
try this :
Quote:

I modified it as
linearInterpolate(alpha*U) & mesh.Sf() in order to get phase flux. I am not sure if this makes sense. 
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