HELP!!! Natural convection with turbulence
 

Now I am simulating natural convection in a square cavity using my own SIMPLER code.
I am using two models :
1. low Reynolds number k-e model; 2. k-e model with wall function and the Ra number is larger than 10^10, but i could not get convergent results, and during iteration, the result will become divergent suddenly.
I made a limitation for k and epsilon. k=max(0,k), epsilon=max(0,epsilon)
Should i make more limitation for other parameters or production term?
I will give my grateful thanks to the people who help me!!
Thanks.
My Email Address is leotsien@gmail.com
or MSN leotsien@msn.com