gravitational acceleration..
 

hi..

I am doing external flow using Fluent, simulation of so2 dispersion from stack. My domain is 4800 m x 250 m x 800 m. i used spalart almaras, energy, and species transport without reaction. I want to use natural convection too.I have tried to running my case with value of g = -9.8 m/s2, but it's very difficult to get convergence, especially in 2nd order discretization. My question is, How is the best value of gravitational acceleration for my case???what is consideration of this value??

thanx for reply

First maybe better to choose lower gravity value. Than increase to 9.8.
The mesh quality is crucial of course!!!!