Hi

I am facing some difficulties when I am trying to compute a high rayleigh number flow.

The main problem is that it is very hard to run to convergence when I treat it as a steady problem.

The other problem is how to difine the time step when I use a unsteady solver. According to the equation which Fluent provided, the time step can be computed by some parameters such as length scale, velocity scale etc. And I am wonder how to define the length scale.

Thx in advance.

Tony

Hi I have the same problem. I find that if I try solve with high velosity I have to choose wery small step size but: first try to find steady solution (not exact of course, first order) then you can use larger step size. or start with small velocity and then speed up now I am preparing Scheme file for speed up If you find some thing more pls let me know via mail.