Boussinesq approximation is used to give density variation with temperature. Everyone says that Boussinesq can be used only for small temperature variation : 1. Can you gave me the value of that maximum temperature variation? (different lues in different papers) 2. What does "temperature variation" or "temperature difference" means? For exemple : Natural convection on a vertical plate uniformly heated. Is the temperature difference between the wall and the fluid or just the temperature difference in the fluid flow (I saw both definition). Thank you

why don't use ideal gas.

I use Incompressible Ideal Gas, but i try to find a paper where limit of Boussinesq is shown (5% for Beta*delta(T) that what I used to ear but I never read it on a paper). Incompressible Ideal Gas not so easy to use. Lot of different depending the operating density you use. It can be unphysical flow when Fluent computes the density as a mean value on all cells. More realistic when I give the operarting density but I don't know what I have to take as specified operating density. If someone have an idea.... (density at the ambiant temperature?)