# natural convection

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 September 18, 2005, 14:06 natural convection #1 rachid Guest   Posts: n/a Hi I am working on simulating the basic natural convection in 2-D. There is a small rectangle (hot brick at constant temperature) and there is the large rectangle (flow field). I have given the temperatures for the brick and two side walls on the outer rect. In the tutorial n.5 they say we can model this similar flow with turning off the radiation model. Which boundary conditions the top and bottom edges should have? I tried wall BC's for the outer rect. and no flow happened. After that i tried p out and p in but the flow in this case occured from the pressure difference What is the correct BCs?

 September 19, 2005, 16:42 Re: natural convection #2 Evan Rosenbaum Guest   Posts: n/a Wall BCs should work. You did specify a temperature-dependent fluid density somehow (i.e., ideal gas, Boussinesq, etc.), right?

 September 20, 2005, 10:21 Re: natural convection #3 rachid Guest   Posts: n/a No i haven't. I suppose you mean the materials panel (Boussinesq) because the radiation model is off. This makes sense though thank you so much... So how do I do that? I mean specyfying a temperature-dependent fluid density. Is there any literature or fluent tutorial you can advise?

 September 20, 2005, 11:04 Re: natural convection #4 rachid Guest   Posts: n/a I found out that thermal expansion coefficient parameter which is available with the boussinesq type density is the key. My new question is: Is it right to define a constant thermal expansion coefficient while it is temperature dependent? (3.47*e-3 K-1)

 September 20, 2005, 12:25 Re: natural convection #5 Evan Rosenbaum Guest   Posts: n/a If you use Boussinesq and if temperatures don't vary too much you can use a constant expansion coefficient. Don't forget to set gravity too.

 September 20, 2005, 14:43 Re: natural convection #6 rachid Guest   Posts: n/a Thank you Evan Rosenbaum. It works!!!

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