Thank you so much for replying. Appreciate it. I can calculate the Richardson number and see if natural convection is dominant or not. I understand that gravity option needs to be enabled when natural convection (or buoyancy effects) are dominant in the flow.
But keeping the natural convection aside for now - does activating the gravity option have anything to do with the flow direction as well? For example, assuming hypothetically that I have a vertical pipe flow and it is under purely forced convection conditions (zero natural convection) - do I still need to include the gravity option just because the flow is in the vertical direction? Or does the direction of flow not matter (and does not need to be considered) when enabling the gravity option? Until now I thought even if natural convection is not present in the flow, we should still enable the gravity option if the flow direction is non-horizontal (i.e., either vertical or at an angle) (I thought this because in normal physics, we take into account the gravity force when we analyze forces in vertical direction or at angles)
Your kind response would be highly appreciated!
Thank you!