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mixture model for cavitation

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Old   March 26, 2009, 17:44
Default mixture model for cavitation
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Kostas
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I have a hydrofoil and i study the cavitation which is showed on it. I use the spalart-allmaras turbulent model and the mixture model for cavitation.
When i run the hydrofoil without cavitation (i dont use mixture model), i take a converge solution, but when i run it with the mixture model i take diverging solution after some iterations (and say: diverge x-mom).

What must i attend ?
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Old   May 13, 2009, 03:31
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Hi there,

If you want I can send you several papers I've published on cavitation modeling in Fluent.
Just send me an email.

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Old   May 15, 2009, 09:54
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my mail is : mech5190@upnet.gr
Send me these paper which tell me.
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Old   March 26, 2011, 18:28
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Hi,
I am currently modeling a marine turbine and I am studying the cavitation effects on the turbine. I am facing the same issue. My first simulations ran very well without cavitation (without the mixture model). But when I try with the mixture model, I get a divergence problem : divergence in AMG solver. I tried to reduce the URF, but it does not work. I tried segregated and coupled solver, but I got the same problem. I am running out of ideas.
Did you finally solved this problem and how ?
Thank you
Jeremie
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Old   March 28, 2011, 01:28
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Hi,

I got some nice results using fluent to model cavitation... you can find them in paper:

Experimental evaluation of numerical simulation of cavitating flow around hydrofoil Original Research Article
European Journal of Mechanics - B/Fluids, Volume 24, Issue 4, July-August 2005, Pages 522-538
Matevž Dular, Rudolf Bachert, Bernd Stoffel, Brane Širok

Give me you're mail so that I'll contact you directly...

Best regards,
Matevz
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Old   March 28, 2011, 10:52
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Hi,
Thank you for your answer.
As I wrote, I want to simulate a marine turbine in a steady water flow with ANSYS FLUENT 12. I study the performances of the turbine. My first simulations ran very well. I reached converged solutions for three different rpm. The conditions were :
- steady-state, pressure-based solver
- NO multiphase model
- Realizable k-e with wall treatment (I used an hybrid mesh with a fine prism boundary layer around the blades)
- Velocity inlet, pressure outlet, rotating walls
- SIMPLE pressure-velocity coupling, second order discretization

With these results, I figured out that I could not ignore the cavitation effects. So I tried the same simulation with the mixture model (with the slip velocity disabled). But the solution diverged after 10 iterations (divergence detected in AMG solver). Then, I tried with the Volume Fraction equation disabled. I thought I was going to get the same results I got with my first simulations, but I still got a divergence detected in AMG solver.
I reduced the URFs, I chose a coupled pressure-velocity scheme, a first-order discretization. But I always got the same divergence issue.
I really don't understand why I cannot reach a converged solution with the mixture model, even with the VF equation disabled.

Thank you in advance for your help.

Regards,

Jeremie
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Old   April 7, 2011, 11:48
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Hi,
I still have difficulties with the cavitation model in Fluent 12, and to get a converged solution with the cavitation model activated (Full Cavitation Model).
So I wanted to have a converged solution without the mixture model, and to be sure of the pressure field. I use a uniform velocity-inlet condition, a pressure-outlet condition, and the domain is closed by walls where a slip condition is set. The operating pressure is set to 0, and I set the static pressure outlet in order to get a total pressure corresponding to the depth of the turbine. I don’t change the default value for the vaporization pressure (2367.8 Pa).
I have some doubts concerning these settings because I read somewhere that the operating pressure should be set equal to the ambient pressure, and the vapour pressure equal to 80000Pa.
Does anyone have some advice about these pressure settings?

Thank you

Jeremie
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Old   April 13, 2011, 22:51
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Hi,Matevz Dular
i got the same problem when i simulated a model Francis turbine with full cavitation.
my email is liwan@whu.edu.cn and send me some papers
Best regards
Li wan
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Old   June 7, 2011, 02:09
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Hi,Jeremie
how about your simulation? i have the same issue about the cavitation.
we can communicate with each other and get some solutions.
my email is liwan@whu.edu.cn
best regards
Li Wan
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Old   November 28, 2013, 13:03
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Hello Matevz,

I am trying to simulate cavitation in journal bearings using the mixture model. Could you send me your papers on cavitation modeling (I may get some help on how to setup my cavitation model in FLUENT).

My email is yousufmansoor@hotmail.com

Cheers,
Yousuf
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Old   November 28, 2013, 13:14
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Hi Yousuf,

You can downoload all my papers from my web page: www2.arnes.si/~mdula

or just type matevz dular in google to find my page.

Best regards and good luck with your work...
Mateus
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Old   November 28, 2013, 16:37
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Hi,

let us concentrate only on the cavitation and not the full cavitation (gas cavitation) which occurs in many industrial applications and needs considering dissolution and absorption of non condensing gas.

First of al: use either the schnell sauer or Zwart-Belarmi.

Mixture model without slip: bubbles won't grow up since the flow is high turbulent and the vapor bubbles are assumed then to flow as quick as the carrier phase.

Start with very tiny time steps: Cavitation is very quick process, mechanic driven and numerical expensive. The most simulations i carried out the time step was below 1e-4/1e-5.

Please do not the singhal mode which depicts one aspect of the ful cavitation model since it's highly instable and is based on old numerical inplementation
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