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Old   April 14, 2009, 18:54
Question Multiphase bubble size
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Hello all,

I am to model a multiphase simulation of an hydraulic turbine (using CFX 11.0) for the first time. To do so, I have to specify the mean bubble diameter, dm, which I find very hard to estimate, especially since the results seem to be very sensitive to this parameter.

Bubble diameter must somehow be related to existing shear stresses and to the surrounding pressure but I don't know how. The only relation I found uses a secret constant parameter "k" multiplying the whole equation and I have no idea of it's order of magnitude, so it's useless.

Does anyone of you have had good experiences modelling bubbles ? How do you estimate their size ? Some people must use these solver capabilities !

Thanks a lot, any help is welcome

Felix
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Old   April 16, 2009, 17:17
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No one has ever tried multiphase in hydro turbines ?
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Old   April 17, 2009, 12:43
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Anton Lyaskin
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I remember I've seen some estimations for simple flows (like pipe flows) - I'll try to find a book later.

BTW, CFX also has MUSIG model, which allow you to specify bubble size distribution instead of just one fixed size.
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Old   April 17, 2009, 14:24
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Anton Lyaskin
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So the book is "Bubbles, Drops and Particles" by R.Clift, J.R.Grace and M.E.Weber. I'll try to look for other publications - I remember I've seen experimental data for bubble size distribution in pumps, which is more or less similar to your case of hydro turbine
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Old   April 17, 2009, 14:46
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Thanks a lot, I'll try to find the book and have a look at it. The MUSIG model looks interesting but I am still stuck with the distribution size estimation. Specifying a distribution must be more adequate though...

Felix
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