Investigation of turbochargers concerning harmonic vibrations

During the development of turbochargers one design criterion involves the amplitudes of harmonic and subharmonic vibrations. When using semi-floating bearings often the harmonic vibrations are dominant and have to be reduced in order to get a beneficial acoustic behaviour.
One main influence upon the harmonic vibrations is the unbalance. Assuming a linear system, a reduction of the unbalance will lead to a reduction of the harmonic vibrations especially in the region of the eigenfrequencies.
During some experimental measurements an increase of the amplitudes in the second resonance was observed, although the unbalance of the rotor was decreased.
Beside the unbalance and its distribution also non-linear effects due to the floating ring bearings can be responsible for the described experimental results.
The aim of the project is to investigate the unexpected behaviour using a numerical model of the turbocharger under transient conditions including a non-linear description of the floating ring bearings.