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iceman February 21, 2008 18:15

cavitation
 
I do some cavitation simulation. And I would like to know what could I take for the value of the Fraction non condensable gaz (water vapor). I begin the simulation with the default value of Fluent and near the implosion I take a smaller value (fraction non condensable gaz)in order to find some good value of the pressure. But the transition is not good, the pressure field is very strange. In some zone I found high pressure value. Has somebody ever tried to change the fraction non condensable gaz and what kind of results did you obtain

Thanks,

NRD February 21, 2008 23:27

Re: cavitation
 
Hello,

I have never tried changing the fraction of non-condensable gases. However, I just wanted to share my thoughts. In my understanding cavitation can either be(i) vaporous (where the liquid evaporates whenever the local pressure drops below the vapor pressure) or (ii) gaseous cavitation (where the entrapped non-condensable gas acts as bubbles). If the gaseous cavitation is not important in your case you can neglect the effect of non-condensable gas. Cavitation will occur if the pressure falls to a value below the vapor pressure. Please correct me if I am wrong.

iceman February 22, 2008 03:56

Re: cavitation
 
In my case when I reduce the value of the fraction non condensable gas (1,5e-05 to 1e-08) I've got a factor 40 on the pressure pick value due to the collapse.

mateus February 25, 2008 06:40

Re: cavitation
 
If I remember correctly you're simulating a single bubble. I think the fraction of non condensable gas only makes sense when you're dealing with many bubbles (attached or developed cavitation) otherwise it should be 0. Also it's a question if mixture model is sinful for single bubble simulation - vof is probably more appropriate.

I hope I helped, MAteus


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