The gravity component manifests itself mostly in potential energy changes as your flow goes through large elevation changes. Additionally the potential energy factor is usually only significant in flows with low dynamic pressure changes (such as low Reynolds number flows.) Is that the case here? You mention your flow rate is 25 L/min but without any sense of scale of this object it's hard to say what your flow velocities are.
I notice that your inlet and outlet are at the same elevation relative to the gravitational potential, and your internal flow cavity looks rather flat, so I don't expect gravity to play a huge role here.
what is the effect of the acceleration on the fluid?
like amit said, the gravity just changes the pressure essentially based on rho g h
an interesting question though, i think you're expecting to have a the acceleration be applied to the flow "molecules" as well?