Air Liquid Mixture simulation in a hydrocyclone
 

I am trying to introduce a mixture of air and water liquid into the inlet of a hydrocyclone design. I figured out that the multiphase model would be suitable for my situation.

However, the problem I have right now is I require a mixture in the composition of 50% air and 50% liquid. I am not sure if Fluent allows this composition. If it is position, how do I set the input fluid to be of such composition?

Eventually, I would require the inlet fluid to be of 60/40 70/30 and eventually 90/10. I require the composition to be both ways. (e.g 90% air 10% liquid or 90% liquid 10% air)

Your case is a two-phas problem.
You define the prominent phase as your primary and the other as secondary in an Euler-Euler scheme like VOF. This is a common multiphase flow boundary condition that after you defined which one is primary and secondary phase, when you specify the inlet value in form of velocity or flow rate, you'll notice fluent will ask a fraction ratio for the secondary phase. And that's where you can enter a range of ratios that you desire.
Note: to say which one, water or air is primary to your problem, I take (for example in your case), if the hydrocylone initially is empty and then mixture of water & air are entering the volume, then I'd assign the primary as air and secondary water. I hope I understood and addressed your problem correctly.

Hi Esma, thanks for the recommendation.

May I ask for your assistance in how I could extract information (volume fraction of air at outlet etc.) Should I be using particle track under Fluent->results for the abovementioned information? Or is there other ways I should do this?