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'Air Ideal gas' density problem

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Old   July 15, 2013, 05:49
Default 'Air Ideal gas' density problem
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Rameez
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I had run a simulation of a stator-rotor combination, for which I had chosen the medium as Air Ideal Gas. After the simulations were done, when i generated report, i was surprised to see the considered density to be 2.23 kg/m-3. Shouldn't it have been 1.2256 kg/m-3? Also how do i rectify it to make it as 1.2256 kg/m-3
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Old   July 15, 2013, 20:31
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Glenn Horrocks
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This looks like an error in your reference pressure. If the reference pressure is 1atm and you have a pressure of 1atm then you have 2atm absolute and densities about 2.2kg/m3.
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Old   July 15, 2013, 23:34
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Thanks a lot for your valuable reply. Could you please respond to the following questions too.
Should i take the reference pressure as 0 atm?
So now do i have to re run the simulations?
And how do i rectify it?
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Old   July 15, 2013, 23:45
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You should put the reference pressure as a typical pressure in your domain. The documentation explains this.

And yes, you will have to redo the simulation as your current results are wrong.
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Old   July 16, 2013, 00:24
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Thanks again. I would like to explain my problem definition-
I had specified the reference pressure as 1 atm

Boundary condition: mass flow inlet to static pressure outlet
So accordingly i plugged in the values as
Inlet: Normal speed as 8.49 m/s
Outlet: 1 atm as my turbomachine opens into atmosphere.
So to rectify the problem of density, should i change the reference pressure as 0 atm or the outlet pressure as 0 atm or some other changes should be done.
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Old   July 16, 2013, 05:51
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Outlet pressure should be zero, reference pressure should be 1 atm.
Either will work fine, as long at they add up to 1atm, but this way is better for round off errors and things of that nature.
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Old   July 16, 2013, 12:45
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Thanks for your help.
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