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Chris June 9, 2004 17:08

How Bubble Radius is Found in Cavitation
I am using the Bubble-Two-Phase Cavitation model within STAR-CD and my question relates to how STAR-CD calculates bubble radius. Neither of the provided materials on the program describes how this is done.

What I want to know is - how is the bubble radius calculated?

Is the Rayleigh-Plesset equation used to calculate this? In the reference for the bubble-two-phase model this is how the author's calculated the bubble radius.

If the Rayleigh-Plesset equation is used to calculate bubble radius, can this equation be modified? More specifically I would like to change the vapor pressure term in the equation (Pv) to something that I specify. This would make my project work flawlessly.

4xF June 14, 2004 12:55

Re: How Bubble Radius is Found in Cavitation
You should find all the information you need in the methodology guide of STAR-CD v3.200. Ask your local support office to provide you with the pages of the manual in PDF-format. If you ask them nicely, I am sure they will also provide you with the CD-ROM of the workshop on Cavitation held in Hamburg last year. FYI, the Rayleigh-Plesset equation is not solved for calculating the bubble radius in STAR-CD v3.150A when using the BTF model.

Chris June 17, 2004 12:19

Re: How Bubble Radius is Found in Cavitation
Thank you for the response 4xF!! Is the methodology guide different from the books that they give you? Also, do you know if the Cavitation models have been updated in version 3.150A vs. 3.2?


4xF June 18, 2004 06:16

Re: How Bubble Radius is Found in Cavitation
a) the methodology guide is the same for everybody, so I do not think I had a special favor in this concern

b) You have definitely more information concerning cavitation modelling in the methodology manual of STAR v3.2 as for v 3.150A

c) You have an additional cavitation model in v3.2 based on the simplified solution of the Rayleigh-Plesset equation for estimating the bubble radius (the term R*d2R/dt2 is neglected, which is a quite good approximation in most cases) You have then: 1) the barotropic model 2) the standard BTF model 3) the Rayleigh BTF model 4) the user-defined model (with SORSCA.F)

I remind you that the cavitation modeling is still a beta feature in STAR v3.150A, although it is fully supported.

Jörn Beilke June 18, 2004 06:38

Re: How Bubble Radius is Found in Cavitation
As fas as i know there are some major bugs in the cavitation models in V315.

Milovan Peric did a presentation about cavitation modeling at the users meeting in London this year, where he told us, that he found a bug in the BTF just some days ago and he wanted to make sure that it will be corrected in V32.

4xF June 20, 2004 11:11

Re: How Bubble Radius is Found in Cavitation
I agree with you concerning this bug (which had an influence onto the respective mass flows calculated for the gas and liquid phase): A source term was missing in the mass conservation equation. But this does not influence the way the bubble radii are calculated in the BTF model though ;-)

Chris June 22, 2004 12:40

Re: How Bubble Radius is Found in Cavitation

Chris June 22, 2004 12:43

Re: How Bubble Radius is Found in Cavitation
Sorry, I messed up that last message. One more question 4xF, can you please tell me how I can modify the Rayleigh-Plesset in STAR-CD?

Because of your responses, I am working to get our STAR-CD updated to version 3.2 and am getting the new methodology stuff that comes with 3.2.

However, in order for my project to work correctly, I need to modify the Pv term in the Rayleigh-Plesset equation, and I'm not sure how to do that in STAR-CD. Any assistance you can provide will be appreciated. Thanks for your help so far!!


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