# symmetry boundary condition

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 October 10, 2012, 08:16 symmetry boundary condition #1 New Member   Sean Join Date: Mar 2009 Posts: 15 Rep Power: 10 I am using symmetry boundary condition, which means I cut the domain into two pieces from the inlet to the outlet. I wonder if I should change the values of mass flow inlet, pressure outlet, hydrualic diameter, turbulence intensity. I know that I should change the value of mass flow inlet to its half, but how about pressure outlet, hydraulic diameter and other parameters? Should they be decreased?

 October 10, 2012, 09:36 #2 Senior Member     Flavio Join Date: Sep 2011 Location: Brescia, Italy Posts: 181 Rep Power: 8 Hi songpen, I think that you should decrease only the mass-flow, the others are intensive property, they don't depend on mass or volume regards __________________ Bionico

 October 10, 2012, 10:24 #3 New Member   Sean Join Date: Mar 2009 Posts: 15 Rep Power: 10 Thank you, Bionico! But if I use pressure inlet and pressure outlet, should I decrease the value because a higer total pressure gives rise to a higher mass in the system? Thank you.

 October 11, 2012, 02:11 #4 Senior Member     Flavio Join Date: Sep 2011 Location: Brescia, Italy Posts: 181 Rep Power: 8 You should not use pressure boundary condition for inlet and outlet as the Manual says (it's unstable), better using mass flow inlet & pressure outlet as you said before Regards __________________ Bionico

October 11, 2012, 03:16
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Quote:
 Originally Posted by Bionico You should not use pressure boundary condition for inlet and outlet as the Manual says (it's unstable), better using mass flow inlet & pressure outlet as you said before Regards
hi mates,
as i remember using pressure boundaries has no limit in fluent, but in CFX there was limitation of using total pressure boundary and static pressure.
also if you wanna use pressure inlet boundary, in symmetry, there is no need to decrease pressure.

October 11, 2012, 08:14
#6
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Sean
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Quote:
 Originally Posted by Bionico You should not use pressure boundary condition for inlet and outlet as the Manual says (it's unstable), better using mass flow inlet & pressure outlet as you said before Regards
Hi, I am using a minus gauge pressure at the outlet to suck gas from a inlet so I need to use outlet pressure. If I use the symmetry boundary condition (then the outlet would be cut into half) and use the same minus gauge pressure, wouldn't the gas be sucked more from the inlet?

Thank you!

 October 11, 2012, 12:00 #7 Senior Member     Flavio Join Date: Sep 2011 Location: Brescia, Italy Posts: 181 Rep Power: 8 No, because there's a simmetry and FLUENT simulates the system taking into account this condition Regards __________________ Bionico

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