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 songpen1985 October 10, 2012 08:16

symmetry boundary condition

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?

 Bionico October 10, 2012 09:36

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

 songpen1985 October 10, 2012 10:24

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.

 Bionico October 11, 2012 02:11

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

Quote:
 Originally Posted by Bionico (Post 386090) 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.

 songpen1985 October 11, 2012 08:14

Quote:
 Originally Posted by Bionico (Post 386090) 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!

 Bionico October 11, 2012 12:00

No, because there's a simmetry and FLUENT simulates the system taking into account this condition :)

Regards

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