Natural Convection in a room
 

Hi guys,

I am trying to simulate natural convection in a room. I have a 150W heater inside and a constant heat flux at the walls to remove the heat from the room.
This is a transient problem. I am using Pressure based solver / Ideal gas / PISO / and changed the under relaxation factors of P to 0.7, and M to 0.3.

My Problem is that I am managing to get the first time step converging, but the next ones are simply vibrating/ oscillating at the same residual..

I don't know what to do !! I have tried various mesh sizes but NOTHING !!!

< PLease HELP >