[shikamaru]

I am stuck with this problem for sometime now. Any help is appreciated.



There is two phases in the domain (air and water – modeling with VOF) . I am trying to maintain a constant level of water in the domain. Top surface is open to atm (0 atm pressure boundary with operating pressure set to 1atm). There is a inlet on the right wall (50mm) with 0.006 m/s velocity through which water comes into the domain. The bottom is a pressure outlet where I am doing a pressure correction based on burnolli’s equation (same as FLUENTS built in target mass flow for single phase). Gravity is turned on.



However, when I use the udf I wrote the mass flow rate oscillates between ±50% of the target mass flow and decreases very very slowly with time.
I thought something was wrong with the udf so I used my udf with 0.05 under relaxation factor (same as fluent) and applied the same problem for single flow. The result was same as what I get when I use targer mass flow in FLUENT. It converges very slowly to the target mass flow.

I tried with the constant pressure boundary condition and found that even without any target mass flow option the mass flow rate at the outlet oscillates. I don’t know why this happens.

Can anyone explain this behavior? Does anyone know why the target mass flow is not available for Multiphase flows or is it even possible to maintain a constant level of liquid for a transient case?

Any suggestions is welcome.