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negative pressure in cfx

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Old   December 18, 2006, 11:13
Default negative pressure in cfx
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i try to build a simulation for a valve. the problem is that whatever i try i get negative pressures about -6kPa in some regions. as i belive pressure below -1kPa could not be possible because the reference pressure is 1kPa. i changed the setup to multiphase fluid with cavitation modelled. as expected in this regions the vapour is present while elsewhere water is dominant. the pressure shown with cavitation beeing set has only positive absolute pressure. therfore in the help file "Ansys CFX-Solver: Modelling" on page 178 is written that ansys clips the pressure values so that they are only positive though they are "less negative than if cavitation is not modelled". the noncliped values could be find under the variable "Solver Pressure" and there are again regions with -6kPa. Does this mean that the negativ values are commonly present and not an error of the solver than more an error of the modelling physics? is there a way to avoid this phenomenon? kind regards, flar.t
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Old   December 18, 2006, 23:20
Default Re: negative pressure in cfx
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liquid in tension = negative absolute pressure

this is physical

physically the flow should cavitate however, it's a CFD solution.... refine the mesh and it should help
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