Modelling Flow from an Exhaust

Bob

Hi, Does anyone have any experience of modelling an exhaust from a large stack or chimney ? I'm looking to start modelling just a single stack but moving on to modelling a stack ontop of a building. The exhaust will be buoyant with a temperature of about 800K and a mass flow rate of about 17 kg/s from an exhasut area of approximate 1.2m^2. My domain is quite large, 200m x 200m x 300m. I'm using CFX5.5. One of the issues I have is on how to model the boundary conditions regarding temperature. Should I be specifying a temperature gradient on the upstream and down stream boundries ? In CFX5.5 there is the option to use mesh adaption, I was considering using this but I'm not 100% sure as to what to adapt to. If I adapt to the temperature then will this only be of use around the exhaust inlet where the temperature gradient is the highest ? is there any way I could get the adaption to may be track the plume away from the exhaust inlet? Finally is there anything I should do to try and create good convergence for this type of problem ??

Sorry this is so long, I look forward to hearing from you Cheers Bob