Thermo-Hydrodynamic Model Influence on First Order Coefficients in Turbocharger Thrust Bearings

Abstract

High rotation turbochargers, to automotive applications, are continually subjected to axial forces due to gas flows in the turbine and the compressor. These axial forces are supported by lubricated thrust bearings, and their effect is introduced in the dynamic system through its equivalent stiffness and damping coefficients. These coefficients are estimated utilizing a thermo-hydrodynamic model of the bearing, which is composed by the Generalized Reynolds Equation and Energy Equation, to estimate pressure and temperature distribution in the oil film. This work analyzes the influence of geometric and operational parameters of the fixed-geometry thrust bearings in pressure and temperature distributions along the fluid film, solving the governing equations by Finite Volume Method. Along with the pressure distribution, the supported axial load is evaluated and, after that, the equivalent coefficients are estimated. In this work, the Energy equation is solved utilizing 3D model and 2D model (neglecting the radial heat exchange), to check the difference in these results in a computationally less expensive model, and other simplifications, disregarding the conduction heat exchange in the circumferential direction and the convection heat exchange in the axial direction. The load capacity and the equivalent coefficients are compared with a purely hydrodynamic model, disregarding the viscosity variation through the oil film. In lower rotational speeds, the heat generated by fluid shear is small, so a HD model can be utilized considering a constant mean temperature of the oil film. This last approach can reduce the cost to solve the pressure distribution that govern the oil flow in the bearing clearance.