# pressure value is strange

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 June 20, 2007, 05:09 pressure value is strange #1 Elyor Guest   Posts: n/a In pump calculation, I specified pressure for inlet (2bar) and outlet (3.5bar), when I run solver I got minus pressure value in some region. What does it mean? Please advise! thanks a lot in advance. Regards

 June 22, 2007, 03:28 Re: pressure value is strange #2 KtoTo Guest   Posts: n/a relative pressure can be minus...

 June 22, 2007, 03:54 Re: pressure value is strange #3 Elyor Guest   Posts: n/a Dear KtoTo, thanks a lot for your reply. As I understand, reference pressure is default pressure which is in Star-CD specified as 0.1MPa. Relative pressure is the pressure we specify as in the boundary conditions. Absolute pressure (pressure from zero point) is the reference pressure(Star-CD default) + relative pressure(the pressure we specify). According to what you are saying if the pressure value in the calculations is negative that means this pressure is lower than that zero point. Is it right? Please elaborate more about this matter Thank you very much in advance.

 June 22, 2007, 04:29 Re: pressure value is strange #4 Mike Guest   Posts: n/a Hi, check if you are getting negative relative or negative absolute pressure. It is ok if you get negative relative pressure as long as it is not more than atm pressure (ref pressure). Now having said that, since its a pump simulation...you may end up having negative absolute pressure due to cavitation. You may have to switch on cavitation model. Hope this helps.

 June 26, 2007, 06:43 Re: pressure value is strange #5 KtoTo Guest   Posts: n/a Hi, Elyor, sorry for long answer. I think that reference pressure is pressure we specify (see also http://www.cfd-online.com/Forum/starcd.cgi?read=12121), relative pressure is computed pressure about reference pressure, and Absolute pressure is relative pressure plus reference pressure (see Post-Processing/Load Data/Data tab, Help). And if relative pressure is negative, that actually means that it is smaller than reference one. I didn't face negative absolute pressure. (may be cavitation effect, see Mike answer) You are welcome.

 June 26, 2007, 06:56 Re: pressure value is strange #6 Elyor Guest   Posts: n/a Thank you KtoTo and Mike, I will try that.

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