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-   -   Cavitation_fluent6.0.12 (solution unstability) (http://www.cfd-online.com/Forums/fluent/32337-cavitation_fluent6-0-12-solution-unstability.html)

Mahdi October 17, 2003 05:55

Cavitation_fluent6.0.12 (solution unstability)
 
Hi all; I want to model the flow field including cavitation arround the geometry proposed by CAV2003 confrence. I work with Fluent6.0.12(bubble dynamics based cavitation model) I use 1e8 for bubble population and 5e-5m for bubble diameters to increase shedding frequency. I start solution with a high cavitation number(by use high operating pressure and a fixed vapor pressure)according to non-cavitating condition and decrease operating pressure to achive my operating cavitation number.When the vf equation go to solved and cavitation occurs, the solution go to an unstable state. Ofcourse my minimum under relaxation number is (.1) But according to toturial suggestion I must use .001 relaxation for vaporization mass.But this is a too too low relaxation number. I am really confused. Thanks.

mateus October 21, 2003 03:33

Re: Cavitation_fluent6.0.12 (solution unstability)
 
Hi!

You are right; Fluent 6.0 cavitation model/solver is very unstable. I couldnt get a valid solution with it. The new Fluent is much better. Otherwise I think that the procedure that you're takanig (the bubble population, diameter...) is corect. You must know that the cav2003 cavitation problem is highly transient - are you solving unsteady? It's also the case of highly developed cavitating flow (in case with 0.4 cavitation number it can be treated as supercavitation which is imposible to simulate with RANS)... You can also check my paper (I used fluent 6.1 and a bit different geometry), I think you can find it under GS9-011...

Good Luck...

MATEUS

ROOZBEH October 21, 2003 04:17

Re: Cavitation_fluent6.0.12 (solution unstability)
 
Hi; But how to model supercavitation with Fluent? Thanks.


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