Natural convection flow crazy fast velocity
 

Hi, I am running a natural convection, buoyancy driven flow problem in Fluent. I have attached a picture for reference. My goal is to find out what the max velocity will be. To minimize mesh size I am just doing 2D for now because the geometry is large. If you look at the picture the right vertical wall is heated with constant temp. The inlet and outlets are exposed to the atmosphere. Initially all the fluid (air) will be at rest and as the right vertical wall heats the air it will rise and create a flow upward. I have defined density, viscosity, thermal conductivity as curve fit polynomials as a function of temperature. Inlet and outlet are pressure inlet and pressure outlets set to 0 gauge pressure and operating pressure was left default 101325 Pa. I am also doing timestep of 0.1s up to 5 seconds (50 timesteps). I am getting crazy fast velocities like over 150m/s.
Thanks