The two-phase, air-water flow pattern in a DynaWhirlpool 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. Among the different operating variables, the back-pressure at the sink outlet affects significantly the flow within the cyclone. The modifications experienced by the flow field as the back-pressure is increased are documented and interpreted. The variation of relevant operating variables is also reported, as the split ratio and the Euler number characterizing the device. It is verified that for large values of the back-pressure the water flow through the sink is hindered and the air core disappears. The flow pattern is moderately altered when the cyclone is fed with a non-Newtonian fluid with the same viscosity as a real water/magnetite dense medium. (C) 2016 Elsevier B.V. All rights reserved.