# 'Air Ideal gas' density problem

 Register Blogs Members List Search Today's Posts Mark Forums Read

 July 15, 2013, 05:49 'Air Ideal gas' density problem #1 New Member   Rameez Join Date: May 2013 Posts: 19 Rep Power: 5 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

 July 15, 2013, 20:31 #2 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 12,638 Rep Power: 98 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.

 July 15, 2013, 23:34 #3 New Member   Rameez Join Date: May 2013 Posts: 19 Rep Power: 5 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?

 July 15, 2013, 23:45 #4 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 12,638 Rep Power: 98 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.

 July 16, 2013, 00:24 #5 New Member   Rameez Join Date: May 2013 Posts: 19 Rep Power: 5 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.

 July 16, 2013, 05:51 #6 Senior Member   Erik Join Date: Feb 2011 Location: Earth (Land portion) Posts: 562 Rep Power: 11 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.

 July 16, 2013, 12:45 #7 New Member   Rameez Join Date: May 2013 Posts: 19 Rep Power: 5 Thanks for your help.

 Tags density

 Thread Tools Display Modes Linear Mode

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is OffTrackbacks are On Pingbacks are On Refbacks are On Forum Rules

 Similar Threads Thread Thread Starter Forum Replies Last Post zhangweisnoopy Main CFD Forum 9 August 12, 2011 08:25 Kevin CD-adapco 0 March 27, 2008 06:55 Miguel Baritto CFX 4 August 31, 2006 12:02 mark FLUENT 3 November 29, 2004 17:40 AB CD-adapco 6 November 15, 2004 05:41

All times are GMT -4. The time now is 00:00.