Mass Loss in Level-Set Tank Simulation After Air Injection

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Hello everybody,

I am simulating, using the Level-Set method, a cylindrical tank partially filled with water (liquid phase, shown in red) and air. The geometry has been reduced to half of the cylinder by applying a symmetry boundary condition. From the bottom of the cylinder, air is injected through a nozzle at a constant flow rate for a time t*. The simulation was run up to a total time t,tot > t* (i.e., also after the injection stops).

Problem: By observing the gif/animation of the phase evolution, the mass (or volume) of the liquid phase gradually decreases over time: the water level keeps dropping and does not return to its initial level once the air injection stops.

My expectation is that, once the air injection ends, the system should return — within small numerical errors — to its initial liquid level. Where is the water “going”? What am I doing wrong in my setup?

Link to movie


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