What does mean adding / oppossing buoyancy in a flow?
 

Hi,

I have a question/doubt regarding a flow with forced convection interacting with gravitational forces (mixed natural / forced convection).
Let's say that we have an horizontal velocity V (Vx,0) in the flow (Vx > 0).
And the gravity acting horizontally as well g (gx,0).

What does it mean adding / opposing buoyancy?
How can I interpret the term "adding"? Does it means gx > 0? or Does it means gx < 0?

Best regards,
Hector.

adding buoyancy is nothing else that introducing the forcing, "opposing" I suppose stands for the sign of the velocity vector opposing to the gravity one. Why are upou considering gravity acting in horizontal direction?

Considering the gravity acting in the horizontal direction is only an artifice.
Let's say that the X axis is set in the vertical line and the Y axis has been set horizontally, perpendiculary to the other axis. It is just that the reference has been turned 90 degrees (to the left).

My understanding is that when you state:
- Adding, it means that the gravity is in the opposity direction of the flow: Vx > 0 and gx < 0.
- Opposing, it means that the gravity is in the same direction as the flow: Vx > 0 and gx > 0.

Adding means
 

Its like water flowing from a tank on vertical pipe. Body force direction and velocity directions are same.

Adding means gx > 0 and vx > 0

When water flows vertically up(by pumping)

then gx > 0 and vx < 0