 ## Fluids

• Diogo Martinho
Subscriber

Hi all,

Probably not a good question but I understand the eulerian model solves a set of equations for each phase. However, when I start my simulation and check the equations I only have a continuity equation and then a vf-gas equation. Is this vf-gas the continuity equation for the secondary phase? • DrAmine
Ansys Employee

By default  only the secondary phase volume fraction transport equation will be solved. With the compatbility condition the volume fraction of the primary phase is calculated.

A bulk pressure continuity equation is always solved.

• Diogo Martinho
Subscriber

So, the continuity equation there (black line) is the primary phase continuity equation. And then I am solving a transport equation for the volume fraction and because of the constraint that the sum of alpha might be equal to one, I have the volume fraction of the liquid phase?

• DrAmine
Ansys Employee

I think I was clear as I wrote we are solving a pressure continuity equation for the bulk and not for the primary phase. The primary phase volume fraction is calculated from the 1-sum_over_all_secondary_phases(volume fraction).

• Diogo Martinho
Subscriber

Ok, thanks.
So, let's say we are simulation water-oil-hydrogen, and they are defined as three phases where, water will be the primary phase and the remaining secondary phases. Will I have a continuity equation for the oil, another for the hydrogen, a continuity equation for the pressure (I am not entirely sure if I understood this equation though) and finally, the water will be 1-sumover_all_secondary_phases(volume fraction)?

• DrAmine
Ansys Employee

Yes. (Pressure Based Continuity Euqation: Check Solver Theory and you will perhaps understand what I am talking about). 