[enoch]

I'm little confused about the form of the buoyant force in two-phase flows.
I wanted to add this force into twoPhaseEulerFoam, which is given by:

alpha*grad(p) ----Eq. (1)

This term is one of the interchanging forces in twoPhaseEulerfoam

or

For phase 1 (or disperse phase),

Vp*(rhoa - rhob)*g ----Eq. (2)

where Vp is the volume of the particle.

I've check the MPIX code where Eq. (1) is adopted and each phase also has the gravity force. Eq. (2) is used in some articles as well.

Which form should be used for the two-phase flow?
Fluent does not show which form is used for multiphase flows in its manual.

Thanks for your comments in advance.