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Old   October 11, 2008, 23:18
Default Atmospheric conditions at boundary
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Hello All,

I have a **large** cylindrical volume. Inside the air is modeled as ideal-gas, compressible fluid. All the walls of the cylinder are supposed to represent infinity: 1 atmosphere, T=300K air. Flow at these walls may happen in any direction.

How do I define these walls? Any ideas are appreciated.

(I tried setting one base and the cylinder wall as pressure-inlets, the other base as pressure far-field. I left all settings at default. I am not sure is this the right way to do it?)
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Old   October 12, 2008, 02:14
Default Re: Atmospheric conditions at boundary
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what is the flow mach number? for M>=0.6 it is recommended to use pressure far field. to do this, you should have a really large volume. if not, generally you should define the BCs as pressure inlet and outlet.
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Old   October 12, 2008, 09:35
Default Re: Atmospheric conditions at boundary
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Thank you for your reply. In the center of domain the flow is subsonic (but close to speed of sound). I am not sure what is the flow speed close to the far boundaries. This is my problem. But I expect it to be 5-20 times slower compared to center of domain.

1) Pressure far-field means flow out, no backflow (maybe I am wrong?). I can't do this, because backflow should occur, as colder air flows into my warmer domain.

2) Pressure intlet/outlet seems better. Here I can fix p=1atm T=300K The problem is I have to fix inflow/outflow kinetic parameters and I don't know what these values are.

Any ideas are appreciated.

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Old   October 14, 2008, 06:30
Default Re: Atmospheric conditions at boundary
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Option 2 in your mind (pressure outlet) seems to be appropriate. You can choose back flow direction specification method as 'from neighboring cell'. You may choose k-e turbulent specification method with values 1-3 but that depends upon your specific case.
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