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Problem to 'CAV' and 'VOF' in cavitation

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Old   December 20, 2006, 11:58
Default Problem to 'CAV' and 'VOF' in cavitation
  #1
Leon
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who can tell me the concrete definition about 'CAV' and 'VOF'. The description in tutorial is so complicated and hard to pronounce!(-: Thanks!
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Old   December 20, 2006, 17:13
Default Re: Problem to 'CAV' and 'VOF' in cavitation
  #2
Sony
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We found him! the last guy who is doing caviation in star-cd instead of star-ccm+!!

star-cd only uses a simplified Rayleigh model. Star-ccm+ has the full Rayleigh-Plesset. You should change.

Some interesting links:

www.ike.uni-stuttgart.de/~www_tfd/pubs/nuclear_2000.pdf green.caltech.edu/colonius/pdfs/PrestonColoniusBrennen2001.pdf

Sony
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Old   December 20, 2006, 17:30
Default Re: Problem to 'CAV' and 'VOF' in cavitation
  #3
William Blake
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Nonsense.

Depending on your fluid you might have to use starv320 instead of ccm+.
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Old   December 21, 2006, 06:38
Default Re: Problem to 'CAV' and 'VOF' in cavitation
  #4
Leon
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Is that serious? I just beginn with some simple cavitation. Must I change to ccm+ now?Is the error between simplified Rayleigh model and the full Rayleigh-Plesset model severe to the same grid?

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Old   December 21, 2006, 16:13
Default Re: Problem to 'CAV' and 'VOF' in cavitation
  #5
Charles
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this is true, for water, oil, fuel, hydrocarbons, ... you need star-ccm+, for chewing gum and yogurt you must use star v3.2 or star v4 with stress analysis

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Old   December 21, 2006, 17:49
Default Re: Problem to 'CAV' and 'VOF' in cavitation
  #6
William Blake
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Try to calculate the cavitation of fuel using ccm+ and you find that the results are not good because the bubbles collapse too fast. This comes from the fact that there is not pure cavitation but cavitation with degassing.

You get quite good results with v320 and the ... model. Later versions of v3 have some problems with the cavitation.
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Old   December 21, 2006, 19:17
Default Re: Problem to 'CAV' and 'VOF' in cavitation
  #7
Leon
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Ok, I will try to change. But,still problem, noboday has calculated cavitaion successfully with Star CD?
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Old   December 22, 2006, 10:57
Default Re: Problem to 'CAV' and 'VOF' in cavitation
  #8
William Blake
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A lot of people have succesfully calculated cavitation with star. You should tell some more details about your problems if you expect some help.
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Old   December 22, 2006, 16:21
Default Re: Problem to 'CAV' and 'VOF' in cavitation
  #9
Vadj
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About cavitation you can go from simple models

1- Rayleigh (old star-cd)

2- Rayleigh-plesset (star-ccm+)

3- Rayleigh plesset + thermal terms + rectified mass diffusion

If you have a code that already has 2-, it is better to star from there a be very familiar with it, then add the additional terms in 3 using field function or user-coding.

If you have a code user-coding to go to 2 and validate or verify your coding. Then add the additional non-linear terms to go to 3-.

For some situation 1- is enough, for other you need 2- (more general). For some specific you need 3-

Usually option 2- is enough because the objective is that your design does not produce cavitation or has the lower chances to cavitates. As soon as there is a hint of cavitation (cavitatoin number, Ca) -> change the design

In University where people study the cavitation phenomena very deep, you need a complex code. Most likely coded internally.

It depends on your context....

Does this help?

Vadj

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Old   December 28, 2006, 22:56
Default Re: Problem to 'CAV' and 'VOF' in cavitation
  #10
wayland
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to William Blake and Sony

how do you think about the VOF technique for cavitation simutating in STAR? maybe there are no big difference between cavitation models at present ,generally, most of which are not very robust to get relatively accurate results.that is to say, we can ignore the model difference and focus on the numerical methods, and is this right?

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Old   December 29, 2006, 16:18
Default Re: Problem to 'CAV' and 'VOF' in cavitation
  #11
Donald
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This is correct. The best choice here is select the code which is the most likely to be most used, i.e. starccm+ here, and of course does not have those bloody extended data.
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