# Multiphase with only one physical fluid

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 June 20, 2007, 03:59 Multiphase with only one physical fluid #1 Terje Guest   Posts: n/a 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

 June 20, 2007, 16:32 Re: Multiphase with only one physical fluid #2 Gert-Jan Guest   Posts: n/a 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

 June 21, 2007, 02:46 Re: Multiphase with only one physical fluid #3 Terje Guest   Posts: n/a 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

 June 21, 2007, 08:18 Re: Multiphase with only one physical fluid #4 Gert-Jan Guest   Posts: n/a 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

 June 21, 2007, 09:05 Re: Multiphase with only one physical fluid #5 Terje Guest   Posts: n/a And could you also have this free slip wall to be convected with the fluid in a transient simulation where the interface is changing?

 June 21, 2007, 11:38 Re: Multiphase with only one physical fluid #6 Gert-Jan Guest   Posts: n/a 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

 June 26, 2007, 08:01 Re: Multiphase with only one physical fluid #7 mac Guest   Posts: n/a 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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