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Multiphase with only one physical fluid

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Old   June 20, 2007, 03:59
Default Multiphase with only one physical fluid
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Terje
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Hi!

- Is it possible to use CFX to model a multiphase system where only one of the phases is treated physically. I am thinking e.g. of an air-water system where the flow of water is only to a small extent influenced by the air and where the computational effort will be greatly reduced by only considering the heavier, more viscous phase.

I know this was possible using Flotran which used to be a part of Ansys, not sure if it is anymore.

Thanks for your help!

- Terje

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Old   June 20, 2007, 16:32
Default Re: Multiphase with only one physical fluid
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Gert-Jan
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Do you mean something like a one-way coupled particle track. With air as continuous phase and water as droplets? This can be done quite easily.

Gert-Jan

www.bunova.nl
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Old   June 21, 2007, 02:46
Default Re: Multiphase with only one physical fluid
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Terje
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Hi Gert-Jan!

No, I do not mean a particle track. Say e.g. tutorial 7 with free surface flow over a bump. Would it be possible to model only the water phase here and say that the forces acting on the interphase was equal to the pressure in air, without explicitly treating the air phase. I do not believe that this would have much influence on the flow of water, but it would greatly decrease the computational effort.

My case is a transient example, where a free surface is evolving in time.

Thanks!

- Terje
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Old   June 21, 2007, 08:18
Default Re: Multiphase with only one physical fluid
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Gert-Jan
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We use free slip walls to model a free surface. As long as the pressures on this free surface are low, the disturbance of your free surface will be low (rho*g*h) and this simplification is justified.

Gert-Jan

www.bunova.nl

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Old   June 21, 2007, 09:05
Default Re: Multiphase with only one physical fluid
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Terje
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And could you also have this free slip wall to be convected with the fluid in a transient simulation where the interface is changing?
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Old   June 21, 2007, 11:38
Default Re: Multiphase with only one physical fluid
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Gert-Jan
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Pfffff, theoretically it should be possible. If you can define a function that describes how to change the surface (and the grid) when the pressure is changing, you should be able to let the free surface float.

Good luck, Gert-Jan

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Old   June 26, 2007, 08:01
Default Re: Multiphase with only one physical fluid
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mac
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Hello I think it's possible to use multiphase option and treat only one component. Try to look in Help for: Algebraic Slip Model (ASM) Regards
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