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visualization of cavitation on propeller blades

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Old   November 15, 2011, 06:38
Default visualization of cavitation on propeller blades
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Emre G
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hi..

how can i visualize the cavitation on propeller blade surface especially vapor/bobble occurrence on surface where cavitation exists?

is a CFD-post software necessary for that?

thanks,
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Old   November 15, 2011, 10:02
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Assuming that you have used the mixture model coupled with one of the cavitational models, you have only to plot contour of vapor fraction of secondary phase (vapor).

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Old   November 15, 2011, 10:49
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hi
residual vf-phase-2 appears allways zero during whole of the transient iteration
other residuals change meaningly.

i dont know why vf-phase-2 doesnt change
could u help me plz
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Old   November 18, 2011, 12:10
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Vapor residual is 0 because in your simulation cavitation doesn't occour for some reasons:
- Are you sure that cavitation occurs? what is your cavitation number?
- What are your boundary conditions?
- What is the quality of your mesh?
- What time step are you using for the transient cavitation?

In my experience you have to use a good quality mesh, with appropriate cell size able to capture cavitation; also you have to use small time step (I often used 10^-6 - 10^-7 s).
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Old   November 18, 2011, 15:04
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hi,

i hav an 10 million tetra mesh >>> 2 million polihedral.
i visualize vapor fraction by displaying contours, it solved cavitation already, but vf-phase 2 still remains zero. pfff.

time step : 1 degree.

..
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Old   November 19, 2011, 07:44
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Cavitation isn't solved if vapor fraction is 0; this means that cavitation doesn't occur in your simulation.
Explain your case:
- are you moving the blade?I haven't experience with moving frames, I only simulated cavitation (steady and transient) by moving the liquid.
- If you are moving the blade, what is the rpm value?For example, if your blade is at 30 rpm you have 180 degree per second, this means that 1 degree is accomplished in 5.55e-3 s..I recommend to low this value till 10^-5 - 10^-6.
- I recommend to check your grid and to size cells where you think that cavitation occurs near 0.125 mm3 (tet size near 0.5 mm).
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Old   November 19, 2011, 17:24
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i didnt say vapor fraction is zero..
i am talking about vapor phase 2 Residual... it remains zero..
observing vapor.
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