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(ASK) negative pressure detected on my outlet. |
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March 21, 2011, 03:27 |
(ASK) negative pressure detected on my outlet.
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#1 |
Member
wibi ario
Join Date: Feb 2011
Posts: 46
Rep Power: 15 |
hi friends
i'm modeling butterfly valve plus pipe in FLUENT 6.2, after i had my simulation then i display my pressure contour, i got my pressure was negative on the outlet, why that happen? regards, |
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March 21, 2011, 05:43 |
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#3 |
Member
wibi ario
Join Date: Feb 2011
Posts: 46
Rep Power: 15 |
i dont have any data about gage pressure, one that i know for sure is just open loop with the asumption that static outlet pressure is 1 Atm. how bout that??
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March 21, 2011, 09:50 |
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#4 |
Senior Member
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ok, your outlet absolute pressure is 1atm. ensure that you set operating pressure correctly. your absolute pressures are evaluated relative to operating one. and double check your boundary conditions.
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March 21, 2011, 21:13 |
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#5 |
Member
wibi ario
Join Date: Feb 2011
Posts: 46
Rep Power: 15 |
i set the operating condition in 1Atm, is it correct?
my boundary condition is velocity inlet and pressure outlet |
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March 22, 2011, 04:09 |
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#7 |
Member
wibi ario
Join Date: Feb 2011
Posts: 46
Rep Power: 15 |
that's what i did, my friend amir but the pressure still negative, why?
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March 22, 2011, 07:22 |
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#8 |
Senior Member
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if you set outlet gauge pressure to 0 pa, the pressure in all cells should be positive unless for supersonic flows or when your case doesn't converge yet. check whether the pressure at the outlet is zero or not and also check residuals.
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March 22, 2011, 07:38 |
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#9 |
Member
wibi ario
Join Date: Feb 2011
Posts: 46
Rep Power: 15 |
i have my case converged obviously. yeah i have checked it and the outlet pressure is zero. any idea what was going wrong? my reynold number is 449.500
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March 22, 2011, 10:58 |
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#11 |
Member
wibi ario
Join Date: Feb 2011
Posts: 46
Rep Power: 15 |
is it normal?does it make a sense?
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March 22, 2011, 20:30 |
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#13 |
Member
wibi ario
Join Date: Feb 2011
Posts: 46
Rep Power: 15 |
yes dear my friend amir i know it usually occurs..cavitation and cavitation is always obtained in the zone where the pressure is below the atmosphere but could it be possible reach negative value???
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March 23, 2011, 02:17 |
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#14 |
Senior Member
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your gauge pressure in those zones is negative not absolute one. (e.g. if you get -1000 pa, it means that your absolute pressure there is 100325 pa) it just shows that pressure there is lower that the value at the outlet.
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March 23, 2011, 04:07 |
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#15 |
Member
wibi ario
Join Date: Feb 2011
Posts: 46
Rep Power: 15 |
so how about if the pressure is positive? for example my inlet pressure is 550.673 Pa, it means that the absolute is 101.325 + 550.673 Pa, right??
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March 23, 2011, 07:46 |
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#16 |
Senior Member
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March 23, 2011, 09:07 |
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#17 |
Member
wibi ario
Join Date: Feb 2011
Posts: 46
Rep Power: 15 |
what an interseting conversation with you, thanks amir may Allah bless you, are u moslem?
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March 23, 2011, 10:56 |
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#19 |
Member
wibi ario
Join Date: Feb 2011
Posts: 46
Rep Power: 15 |
me too.
amir |
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