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Thomas April 16, 2002 03:08

Twin-fluid mixing
Hi I am mixing water and air in a mixing chamber. The angle between the inlets to the chamber is 52 degrees. The water is flowing with 7 m/s and the air with 140 m/s. I am using the k-e model in a transient simulation. When using the homogeneous approximation, I get much too high velocities and pressure.

Does anyone have experience with this kind of problem in CFX4?

Kind regards Thomas

Mike April 16, 2002 19:42

Re: Twin-fluid mixing
I'm not sure if the homogeneous model would be valid. I don't have any experience with CFX-4, but if the homogeneous model is solving for a single velocity field (check in the documentation) then it's not valid for a dispersed air phase in water (i.e. air bubbles in water). A multiphase model that solves for a single velocity field would be used, for example, in free surface flow where both fluids are continuous. A Particle model would be more appropriate for multiphase mixing applications.

Thomas April 17, 2002 02:54

Re: Twin-fluid mixing
The flow in the domain is with a film of water at the side walls and only a few drops in the centre, where the air is flowing. Therefore I figured that the homogeneous model, which only solves for one solution field, would be appropriate (2 continuous phases).

Is it possible that a solution is easier reached when using a mixture in the two inlets (99 vol% air and 1 vol% water in one inlet and vice versa in the other inlet) rather than using pure air and water ?

Mike April 17, 2002 19:34

Re: Twin-fluid mixing
I wouldn't have thought that would help since 1% water would be a dispersed phase. Not sure what else to suggest without seeing the geometry. How does the water form a thin film at the walls - is the domain spinning? I'm guessing you'd need a fine mesh to resolve the film - say at least 10 nodes across the thickness of the film.

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