Nonlinear dynamics characteristics of a tilting pad journal bearing supported turbocharger

In order to enhance the stability of the turbocharger rotor system, the nonlinear dynamic characteristics of the turbocharger supported by tilting pad journal bearings are analyzed in this study. After the nonlinear oil film force model for tilting pad journal bearings is derived based on the short bearing approximation and considering the circumferential swinging of the pads, the nonlinear vibrations of the turbocharger supported by tilting pad journal bearings subjected to unbalanced excitation are investigated. Through an analysis of the vibration response of the rotor system at various rotational speeds, it was observed that the turbocharger rotor system supported by tilting pad journal bearings demonstrates improved stability performance in comparison to the other types of bearings in existing studies. The turbocharger exhibits stable periodic motion at low to medium rotational speeds and quasi-periodic motion at high rotational speeds. What's more, the impact of bearing parameters on the nonlinear dynamics characteristics of the turbocharger rotor system is discussed. Results from the discussion of bearing parameters indicate that increasing the pad preload, oil film viscosity, and pad angle, and reducing the radial clearance when the relative eccentricity is small can all increase the bifurcation point speed and enhance the system's stability. Furthermore, increasing the pad angle suppresses the amplitude of sub-synchronous vibrations in the rotor system. The research findings provide some suggestions for the design considerations for tilting pad bearings applicable to turbochargers.