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-   -   cavitation bubble collapse (http://www.cfd-online.com/Forums/fluent/47092-cavitation-bubble-collapse.html)

iceman January 21, 2008 17:50

cavitation bubble collapse
 
Hi Does somebody try to simulate the collapse of a water vapor bubble? I initialize Fluent 6.3 with a radius bubble of 5 mm Pv=2360Pa and a fluid (water) pressure of 100000Pa (1bar).The mesh is a quarter of a circle, on one segment I impose the boundary condition axis and for the other segment I impose a symmetry condition and I use the 2D axisymetric solver. I use a time step of 1e-07s, k-eps realizable, mixture model. With these parameters I could see the collapse in about 6e-04s (experiment: 4,5e-04)but the pressure due to the collapse at 3mm and 10mm of the bubble center are very low compare to the experiment (I find 3 and 1,5 bar compare than 250 and 80). I try to use a smaller step time, Quick scheme but it s not better. So if somebody has the solution or an idea it would be nice.

Thanks

iceman January 22, 2008 15:51

Re: cavitation bubble collapse
 
Nobody for my problem??

mateus January 24, 2008 06:04

Re: cavitation bubble collapse
 
Hi,

It's interesting what you do...I tried to do something similarly some time ago. But no success. I think the problem is much more complicated as it looks. I think you at least need to treat both fluids compressible. Why do you use k-e model? If you have so tiny (and dense) mesh it's hard to talk about turbulence...I think you can use laminar flow...

I know I didn't help you much but maybe we could try to do something together...

Mateus


iceman January 24, 2008 08:18

Re: cavitation bubble collapse
 
I'm going to simulate using laminar flow. I tried to simulate using the option ideal gaz for the vapor but it didn't work, there was water liquid inside the water vapor (it's not very physic) What was the size of your bubble ? me 4,15mm the time step? me 1e-07 and 20 iterations per time step but I need to initialize with 1e-07 and 150 iterations per time step during 100 iterations. Did you see the collapse ?

Somebody tells me that Knudsen number is not very low for this simulation, so the Navier-Stokes equations may not be used for this problem, what do you think about that?

I'll be there in 6 hours bye

Iceman

ROOZBEH January 31, 2008 18:58

Re: cavitation bubble collapse
 
Hi friends;

I have simulated formation of the near wall collapsing bubble induced jet using Fluent and submit a journal paper about a subject related to this phenomenon. Be sure that if the bubble size is in order of 1mm, the flow field is laminar. I applied VOF approach. Using mixture approach will be failed because there is a sharp interface between the vapor inside the bubble and the outside water. I assumed compressible gas inside the bubble and incompressible liquid outside the bubble. One important matter is that when you assume the incompressible liquid, you should set an outlet as a part of the outer boundary of your solution domain.

regards, ROOZBEH

iceman February 5, 2008 17:28

Re: cavitation bubble collapse
 
What do you put for fraction gaz non condensable ?? Why do you use compressible gaz? Could you send me your paper about the collapse bubble??I m very interested by this.

Thanks

Iceman

ndabir June 18, 2012 13:17

Hi

have you solved your problem? I am doing the same simulation but I can't see the collapse of bubble. Does it have any trick for simulation? could you please let me know what was your problem and how did you solve it? I am using first order upwind for my simulation. Do you think I should use second order?

Thank you


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