Experimental and Analytical Investigation of Turbocharger Whirl and Dynamics

Abstract

The objectives of this investigation were to experimentally and analytically investigate the dynamics of a medium-sized, relatively high-speed ball bearing–supported turbocharger (TC). In order to achieve the objectives, a TC test rig was designed, developed, and instrumented with a combination of strain gauge–based load sensors and proximity probes. The sensors were used to measure the axial and frictional loads on the TC bearing, as well as the whirl of the compressor and turbine rotors, under various operating conditions. In this TC, the compressor and turbine shaft are supported by a pair of unloaded back-to-back angular contact ball bearings. The bearing cartridge is supported by squeeze film dampers (SFDs) and is prevented from rotation by an anti-rotation pin. To achieve the analytical aspects of this investigation, an equivalent bearing model was developed to investigate the bearing dynamics and whirl of the TC rotating assembly. The TC bearing cartridge was modeled with a single deep groove ball bearing (DGBB) using the discrete element method. The rotating shaft, compressor, and turbine were considered to be rigid and integrated with the inner race of the bearing. The SFD that supports the bearing was modeled with a bilinear spring and damper. A DGBB was used because it can support axial load in both directions. The results from the analytical model correlate well with the experimentally observed loads and whirl and show that whirl can have a significant effect on the dynamics of the individual bearing components.