Well, when I set the forced convection simulation, the air was indeed flowing from +Z to -Z boundary faces. But, when I “shut down” this flow and let only natural convection takes place, the fluid, due to buoyancy effects, starts to flow from -Y to +Y, if I am thinking right.
So, I was going to ask you exactly what you’ve just said: it is better to invert the dimensions of the fluid region, right?
Best,
Gabriel