Just wonder if I have to consider gravity effects in my flow simulation. As far as I know when you tick the gravity box,it means that you consider natural convection in the analysis. My model is a hollow cylinder with a bar in the middle as a volume heat source. I ran the analysis  with and without gravity and I got these 2 plots(attached) for velocity in fluid (air).  The one with gravity, I used -9.81 m/s^2 in Y direction and used Y axis as reference in wizard. But I cannot intemperate them. Can someone explain why I got these results for the velocity please?