[Michael VF]

In Ansys CFX I modeled how air (at atmospheric pressure) ejects into fast water flow, which is produced by several ejectors.
I wanted to have 50/50 output of mixed air/water on outlet.
But the results are kind of suprising for me: air is ejected, but somehow stucked near the outlet. So the average air mass flow rate at the end of the model is equal to 0 (see the screenshot).
Does this result make sense and explainable or there should be some error in my setup?

As for my CFX setup, I set mass flow rate for water on inlet, set average pressure at air inlet (1 bar) and at outlet (to 0.25 bar) and selected "bubbles mode".
And one more question is Ansys ("multiple fluid" mode) capable for doing such calculations (e.g. air ejection)?

[ghorrocks]

In the startup transient I would expect that air would get trapped in a recirculation and have to build up before it started to flow to the outlet. So you might just have to run the simulation longer. Are you running this steady state or transient?

What is "bubbles mode"?

CFX has an extensive range of multiphase models. So you can say with some confidence that CFX can model this flow. But multiphase models are challenging simulations and require careful choice of physical model and other issues. Recommended for experienced CFD people only.

[Michael VF]

What is "bubbles mode"?

I use "Tools" -> "Quick setup mode", and select for "Multiphase option" = "Bubbly flow".
I also tried "Cavitation".
Another question from my side is: Does Ansys CFX simulate dissolution of air in the water?
Ansys says that mass flow of air through the outlet is zero. But does it mean that it does not take dissolution into account?

[ghorrocks]

CFX has many, many multiphase models. You need to know what they are and what they are useful in modelling before selecting a multiphase model. For instance the cavitation model is used to model cavitation (obviously) - that is of no relevance here.

CFX can simulation air dissolving in water. You have to set up an interface mass transfer model to do this. Again, this is another physical model which you have to understand. You cannot just click a button and it happens.

I recommend you read the CFX documentation on the various multiphase and multicomponent mixture models it uses. Then you will know what models you want to implement.