The effect of three-lobed bearing shapes in floating-ring bearings on the nonlinear oscillations of high-speed rotors

Floating-ring bearings are widely used in automotive turbocharger machinery because of their robustness, low cost and their suitability under extreme rotation speeds. This type of bearings, however, can become a source of noise due to oil whirl/whip instability. The stabilizing effect of lobed bearing shape is known in the literature, which encourages the researchers to substitute plain cylindrical full floating bearings with lobed geometries in their outer and inner clearances to prevent the rotor-bearing system from developing oil whirl/whip instability or to reduce its amplitude of response when oil whirl/whip instability takes place. In this study, a novel concept of a floating-ring bearing with three-lobed clearances in its inner and outer films is modelled. In order to perform transient simulations, a very time-efficient approximate solution for the Reynolds equation to the geometry of three-lobed bearings is presented. Using the run-up simulation method, the nonlinear dynamic behaviours of a real turbocharger rotor supported by the novel concept of three-lobed floating-ring bearings are systematically investigated. The newly obtained results show that the sub-synchronous vibrations can be thoroughly suppressed with high preload factor at the cost of a moderate increase in the synchronous vibrations. Hence, the three-lobed floating-ring bearings design is an attractive alternative to plain cylindrical floating-ring bearings for automotive turbocharger applications.