Influence of Different Geometries of Hydrodynamic Bearings in the Dynamic Response of a Rotating System

Hydrodynamic bearings are widely used in rotating machines, being the element responsible for the interaction between the rotor and the supporting structure. Therefore, in order to describe the dynamic behavior of the rotating shafts, it is necessary to know the journal bearings dynamic characteristics. For this reason, this work aims to analyze the influence of three different geometries of journal bearings when operating in a small turbocharger for vehicular application, which implies in high rotation speed and load capacity. In this paper the analysis will be done through the frequency response of the proposed system and the equivalent damping and stiffness coefficients coming from the oil film present in the bearings. These dynamic coefficients are obtained with a spring-damper approach, in order to represent the inherent flexibility and damping of the oil film. The equivalent coefficients of the journal bearings are derivated by computational simulation, solving the Reynolds equation. In this case, the coefficients are evaluated by the perturbation theory applied to the displacements and velocities of the shaft center inside the bearings. Thus, the main goal of this paper is to analyze the frequency response of the system as well as the equivalent dynamic coefficients obtained for the three different bearings and verify the sensitivity of these bearings in the frequency domain response of the shaft-bearing system.