Multiphase Mixing Tank
 

Hello,

I am working in a project about the simulation of a mixing tank bioreactor. For now, I would like to work only with water and air, with the air phase initially above the water, in a batch tank, no inlet or outlet (see attach. 1). I have a doubt about how to define the initial air phase. In the present model, I created the vessel with two domains and defined the air volume fraction = 1 in the upper domain and air.vf = 0 in the water domain and connected them with interface. I used a Turbulence Homogeneous model: k-epsilon, defined air as dispersed fluid and water as continuous, surface tension with drag coefficient and the top boundary as opening relative pressure = 1 atm. I am having some strange results, such as a higher water velocity in the air phase (see attach. 2), even though the water vol. fraction is 0. Moreover, the water velocity around the impellers is quite lower than I should expect.

Any thoughts?
Thank you in advance.