Static Pressure Opening

will321321 · February 18, 2015, 23:53

Hi Gentlemen,

I'm a bit confused on the boundary condition static pressure Opening here are a couple of thing on my mind.

1. For example i want to specify -5 Pa in the Opening I used the absolute pressure right? (101320 Pa)

2. For my simulation I do not know what the temperature is on the static pressure opening, that's the variable i want to determine, could I in some way disable the temperature under thermodynamic parameters?

Thank You!

Boris_M · March 2, 2015, 07:47

Hi Will,

The pressure is always the abslute pressure you have to define. Reason for that is because different industries might have different default pressure they work from so it is clear which pressure you really use you have to specify the absolute pressure.

In your case if you want to have it -5 Pa under 1 atm then you have to specify 101320 Pa.

The temperature is only important to define if it is an inlet opening. If the temperature changes in the model then the oultet will have the corresponding temperature. Only if you have an error message during the solver saying "Vortex crosses the pressure opening" it means that there is flow coming into the outlet due to a vortex that sits right near the outlet and causes flow to leave but also to enter through the pressure opening. Only then the incoming flow has the specified temperature and will create wrong results at the outlet if you use a surface goal for the bulk average fluid temperature. Reason is that the average is wrong due to the fixed inflow temperature specified and another outflow temperature. So make sure in such a case that the outlet is extended so that the vortex is not causing an inflow at the opening.

Boris

will321321 · March 2, 2015, 20:24

Hello Boris,

You are absolutely correct, the warning "vortex crosses the pressure opening" does occur on the outlets and contaminates the temperature giving me incorrect results.

My dilemma is, when I extend the outlets, to get rid of the warning, the warning does not disappear. I have already tried extending my outlets up to 10 times the duct diameter.

Is it possible to make the pressure opening's temperature dependent on the surface goal "bulk average fluid temperature"?.

Thank you for the help!.

Will

Boris_M · March 3, 2015, 04:11

Hi Will,

no, this is not possible and you would just create a loop that might not find an end.
It is very unusual to have such a long extension and still get this error message. Did you wait till the calculation converges?
Sometimes the message appears and it just takes some time until it vanishes. Important is that the message is gone at the end of the calculation.

Other than that I cannot tell how to fix it without seeing the model or the outlet flow and how and where the vortex is.

Boris

February 18, 2015, 23:53	Static Pressure Opening	#1
will321321 New Member Join Date: Apr 2014 Posts: 29 Rep Power: 12	Hi Gentlemen, I'm a bit confused on the boundary condition static pressure Opening here are a couple of thing on my mind. 1. For example i want to specify -5 Pa in the Opening I used the absolute pressure right? (101320 Pa) 2. For my simulation I do not know what the temperature is on the static pressure opening, that's the variable i want to determine, could I in some way disable the temperature under thermodynamic parameters? Thank You!

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March 2, 2015, 07:47		#2
Boris_M Disabled Join Date: Jul 2009 Posts: 616 Rep Power: 23	Hi Will, The pressure is always the abslute pressure you have to define. Reason for that is because different industries might have different default pressure they work from so it is clear which pressure you really use you have to specify the absolute pressure. In your case if you want to have it -5 Pa under 1 atm then you have to specify 101320 Pa. The temperature is only important to define if it is an inlet opening. If the temperature changes in the model then the oultet will have the corresponding temperature. Only if you have an error message during the solver saying "Vortex crosses the pressure opening" it means that there is flow coming into the outlet due to a vortex that sits right near the outlet and causes flow to leave but also to enter through the pressure opening. Only then the incoming flow has the specified temperature and will create wrong results at the outlet if you use a surface goal for the bulk average fluid temperature. Reason is that the average is wrong due to the fixed inflow temperature specified and another outflow temperature. So make sure in such a case that the outlet is extended so that the vortex is not causing an inflow at the opening. Boris

March 2, 2015, 20:24		#3
will321321 New Member Join Date: Apr 2014 Posts: 29 Rep Power: 12	Hello Boris, You are absolutely correct, the warning "vortex crosses the pressure opening" does occur on the outlets and contaminates the temperature giving me incorrect results. My dilemma is, when I extend the outlets, to get rid of the warning, the warning does not disappear. I have already tried extending my outlets up to 10 times the duct diameter. Is it possible to make the pressure opening's temperature dependent on the surface goal "bulk average fluid temperature"?. Thank you for the help!. Will

March 3, 2015, 04:11		#4
Boris_M Disabled Join Date: Jul 2009 Posts: 616 Rep Power: 23	Hi Will, no, this is not possible and you would just create a loop that might not find an end. It is very unusual to have such a long extension and still get this error message. Did you wait till the calculation converges? Sometimes the message appears and it just takes some time until it vanishes. Important is that the message is gone at the end of the calculation. Other than that I cannot tell how to fix it without seeing the model or the outlet flow and how and where the vortex is. Boris