how to set exit pressure correctly?

sms1424 · April 26, 2016, 14:54

Hey Guys,

I'm simulating turbulent flow inside square duct, with known inlet velocity and exit pressure. The value for exit pressure is 15 pa gauge.

I'm not sure how to set this 15 pa in star ccm+, I just used the outlet region and specify the pressure there to be 15 pa. Is that right? do I have to enter the gauge pressure or absolute pressure in this case?

Also, one more thing, If I want to plot the pressure along the duct, do I have to use " pressure" or "static pressure"? and is the difference between them?

Any input from you is very helpful!

Thanks!

fluid23 · April 26, 2016, 16:49

The pressure you specify in the outlet boundary will be gauge pressure referenced to whatever value you enter into the reference pressure under continua>physics>reference values. If you know your exit pressure in guage, just enter it and make sure your reference pressure is set to whatever ambient pressure is appropriate.

I believe the difference between pressure and static pressure involves gravity. Static pressure is a spherical tensor acting on the fluid that is independent on height. Pressure will be static pressure plus piezometric head. If you don't have gravity physics model selected they will be the same. For air, the difference will be fairly negligible but if you have a dense fluid like water then it could make a noticeable difference.

April 26, 2016, 14:54	how to set exit pressure correctly?	#1
sms1424 New Member sulaiman Join Date: Feb 2016 Posts: 18 Rep Power: 10	Hey Guys, I'm simulating turbulent flow inside square duct, with known inlet velocity and exit pressure. The value for exit pressure is 15 pa gauge. I'm not sure how to set this 15 pa in star ccm+, I just used the outlet region and specify the pressure there to be 15 pa. Is that right? do I have to enter the gauge pressure or absolute pressure in this case? Also, one more thing, If I want to plot the pressure along the duct, do I have to use " pressure" or "static pressure"? and is the difference between them? Any input from you is very helpful! Thanks!

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April 26, 2016, 16:49		#2
fluid23 Senior Member Matt Join Date: Aug 2014 Posts: 947 Rep Power: 18	The pressure you specify in the outlet boundary will be gauge pressure referenced to whatever value you enter into the reference pressure under continua>physics>reference values. If you know your exit pressure in guage, just enter it and make sure your reference pressure is set to whatever ambient pressure is appropriate. I believe the difference between pressure and static pressure involves gravity. Static pressure is a spherical tensor acting on the fluid that is independent on height. Pressure will be static pressure plus piezometric head. If you don't have gravity physics model selected they will be the same. For air, the difference will be fairly negligible but if you have a dense fluid like water then it could make a noticeable difference.