The Rayleigh Benard instabilities are a phenomena that seems to have various applications. This study allowed us to visualise many theoretical results about the convection of Rayleigh Bénard with the simulation code FLUENT. We have shown that under the critical Rayleigh (Rac=1708),  the flow was purely diffusive (no velocity in the fluid and  temperature gradient  linear) and that over the critical Rayleigh, the flow began to be convective (appearance of convection rolls).
        On one hand, we have checked that the computation of Rac was in good agreements with the theoritical prediction. We also checked that the unsteady calculations tend to the results of the steady model, if time increases. On the other hand, we tried to draw users' attention on the results given by FLUENT. For that, we have taken a turbulent case and calculated it with both laminar and turbulent models. All these results do not bring something really knew about the Rayleigh Benard instabilities but let the users of FLUENT know better the results they get and what they can conclude from them.