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absolute negative pressure????

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Old   October 27, 2003, 01:35
Default absolute negative pressure????
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john
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Hi All,

I have simulated a flow in a closed channel involving water. But to my surprise I am getting -ve absolute pressure at many locations which is weird. Can anybody tell where things went wrong, if anybody faced similar problem before....

Thank you.

John
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Old   October 27, 2003, 04:25
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Anton Lyaskin
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May be in the real flow there should be cavitation?
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Old   October 27, 2003, 05:20
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john
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Thanks a lot Anton for your reply. But I did not understand the basis of your conclusion of cavitation. Do you mean to say if the cavitation model is not on the code has no other option than putting -ve presure values to satisfy continuity equation? Let me know if I am absolutely wrong or any other logic is there. Thanks again. - John
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Old   October 27, 2003, 06:50
Default Re: absolute negative pressure????
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Anton Lyaskin
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The code dosn't care about ABSOLUTE pressure (in case of incompressible flow) - it deals with RELATIVE pressure. So from the point of view of mathematics your solution is correct - your pressure field does satisfy the continuity equation, because it's written for relative pressure, and there are no limitations for it. So you don't need to turn on cavitation model to satisfy the continuity.

But from the point of view of physics, absolute pressure in liquid can not be lower than some certain value (saturation pressure). Basicaly, all of your regions with negative absolute pressure will correspond to cavitation bubbles filled with saturated vapour (this is a bib-bib-big oversimplifaction).
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