# Buoyancy Driven Flow - HELP!

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 October 8, 2007, 03:16 Buoyancy Driven Flow - HELP! #1 Carlos Guest   Posts: n/a Hello, I have been modeling steady state vehicle aerodynamics for a few years now and I am faced with a simple problem yet I can't seem to get a solution, can anybody help me? I have a land rover and a livestock trailer. In most of my simulations of turbulent flow, air flows through a duct surrounding the vehicles and that is simple enough. However, I want to look at a flow speed of zero. There are CAD models of animals which I have inside the livestock trailer and they produce heat. I just want to model the temperature gradients inside the trailer. I have followed the help in Fluent and changed the boundary conditions of the duct I used for airflow calculations. So now, all the external boundaries are pressure outlets at asmospheric pressure and the vehicles and animals are walls. However, the solution always diverges. What am I doing wrong!?! Can anybody give me a simple overview of the steps required to model this type of flow? Thank you for your time. Best regards, Carlos.

 October 8, 2007, 17:10 Re: Buoyancy Driven Flow - HELP! #2 red lemon Guest   Posts: n/a Use body force weighted for pressure, gravity enabled, ideal gas and ensure boundaries are far enough away from heat source

 October 11, 2007, 02:35 Re: Buoyancy Driven Flow - HELP! #3 Rameche Candane Guest   Posts: n/a Are you specifying isothermal wall as BC for the livestocks or u treat them as conjugate heat transfering sources with volumetric heat generation. I agree with red melon you need to specify the gravity as -9.81m/s2, and enable ideal gas assumption. Its not a must to have the boundary quite far away as u r specifying pressure BC.

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