Analysis of rotors supported by thrust bearings

Thales Freitas Peixoto¹; Leonardo Carpinetti Vieira¹; Katia Lucchesi Cavalca¹

¹ UNICAMP

doi:10.20906/CPS/COB-2015-0183

Resumo

The assembly of a rotary machine, formed by a rotating shaft supported by bearings, is called rotor. A very specific class of rotors is the high rotation turbochargers, to automotive application. In these turbochargers, the shaft, where the rotors are mounted, is continually subjected to an axial force because of the gas acting on the turbine and the compressor with different magnitudes, and these forces cannot be supported by the radial lubricated bearing, which causes an axial displacement of the shaft. Therefore, thrust bearings are necessary to absorb these forces and displacements, avoiding direct contact between the solid surfaces, which means that the lubricated thrust bearings must be designed so that the fluid film sustain the shaft axially, avoiding friction and premature wear in the bearing surface. In this work, models of segmented thrust bearings of fixed geometry are used, which are linearly modeled by equivalent stiffness and damping dynamic coefficients. These coefficients are obtained through the linearization of the hydrodynamic force generated by the pressure distribution in the bearing pads, which results because of the relative movement between the bearing and the collar fixed to the shaft. Numerical simulations are accomplished utilizing a model of concentrated parameters, where all the mass is concentrated in the shaft collar, and a model by finite element method (FEM), wherein the shaft, rotors and bearings are properly discretized. The sensitivity of the thrust bearing model to the discretization is analyzed and the response of the system to impulse and step inputs are obtained and compared for both models of the system. Significant parameters like natural frequencies and the displacement amplitude at the collar node are also evaluated and compared.

Palavras-chave: Hydrodynamic Thrust Bearings; Rotor Dynamic Analysis; Stiffness and Damping Coefficients