Stability Analysis of a High Speed Automotive Turbocharger

Automotive turbochargers are known to have operation into the linear unstable region. The operation in the nonlinear limit cycle has been tolerated on most applications to date. The need for quieter, smoother operation and reduced emissions has prompted new evaluations of the rotor bearing design for these systems. In this research a commercial rotordynamics computer program is used to evaluate the stability and transient response of a high speed automotive turbocharger. Various models with varying bearing designs and properties have been solved to obtain the linear stability threshold speeds and also the non-linear transient response. The predicted whirl speed map shows two modes of instability and is very similar to the limited test results in the literature. The calculation process is discussed in detail and the results of the current research will be compared to the literature. An experimental research project is currently in progress at Virginia Tech and those results will be documented in a future publication.