visualization of cavitation on propeller blades

emreg · November 15, 2011, 05:38

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,
emreg

ghost82 · November 15, 2011, 09:02

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).

Daniele

emreg · November 15, 2011, 09:49

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

ghost82 · November 18, 2011, 11:10

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).

emreg · November 18, 2011, 14:04

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.

..

ghost82 · November 19, 2011, 06:44

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).

emreg · November 19, 2011, 16:24

i didnt say vapor fraction is zero..
i am talking about vapor phase 2 Residual... it remains zero..
observing vapor.

November 15, 2011, 05:38	visualization of cavitation on propeller blades	#1
emreg Senior Member Emre G Join Date: May 2011 Location: Turkey Posts: 126 Rep Power: 14	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, emreg

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November 15, 2011, 09:02		#2
ghost82 Senior Member Rick Join Date: Oct 2010 Posts: 1,016 Rep Power: 26	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). Daniele

November 15, 2011, 09:49		#3
emreg Senior Member Emre G Join Date: May 2011 Location: Turkey Posts: 126 Rep Power: 14	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

November 18, 2011, 11:10		#4
ghost82 Senior Member Rick Join Date: Oct 2010 Posts: 1,016 Rep Power: 26	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).

November 18, 2011, 14:04		#5
emreg Senior Member Emre G Join Date: May 2011 Location: Turkey Posts: 126 Rep Power: 14	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. ..

November 19, 2011, 06:44		#6
ghost82 Senior Member Rick Join Date: Oct 2010 Posts: 1,016 Rep Power: 26	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).

November 19, 2011, 16:24		#7
emreg Senior Member Emre G Join Date: May 2011 Location: Turkey Posts: 126 Rep Power: 14	i didnt say vapor fraction is zero.. i am talking about vapor phase 2 Residual... it remains zero.. observing vapor.