Numerical investigation of rotors in floating ring bearings using co-simulation

The nonlinear oscillation behavior of rotors in floating ring bearings is investigated numerically by means of transient run-up simulations. A mass-conserving cavitation model based on two-phase theory is employed. Special axial boundary conditions are introduced, which better reflect open-ended bearings. The rotor and bearing models are implemented in commercial software tools and coupled using a co-simulation coupling method, which enables the creation of detailed, easily interchangeable and updateable subsystems. Simulations are performed using a symmetric Jeffcott rotor and an asymmetric, heavy turbocharger. The differences between classical non-mass-conserving and the mass-conserving two-phase cavitation model are small for purely synchronous oscillations. The pressure build-up is delayed for the two-phase model during radial squeeze motion of the journal, which decreases the damping of the bearings. This entails a lower stability threshold rotor speed of the subsynchronous whirls and may also yield higher journal eccentricities.