The two-phase, air-water flow pattern in a DynaWhirlpool type centrifugal separator is investigated using time-dependent, three-dimensional numerical simulation. The air-water interface is captured by the Volume-Of-Fluid approach, while the unresolved turbulence fluctuations are modeled via a second-order differential-stress turbulence model. The methodology is validated with available laser-Doppler data acquired on a similar separation device. The velocity field within the cyclone is thoroughly characterized for a single operating condition, revealing the presence of a stable air core that flows axially faster than the surrounding water.