Determination of a Numerical Surge Limit by Means of an Enhanced Greitzer Compressor Model

Authors

Tobias Haeckel  - TU Darmstadt, Germany
Dominik Paul - HS RheinMain, Germany
Sebastian Leichtfuß - TU Darmstadt, Germany
Heinz-Peter Schiffer - TU Darmstadt, Germany
Werner Eißler - HS RheinMain, Germany

Abstract

The surge limit of compressors is one key parameter in the design process of modern turbocharger compressors for automotive applications. Numerical methods like steady-state simulations are state-of-the-art methods for predicting the performance of turbocharger compressors in an industrial environment. Transient, time-resolved numerical simulations of a complete compressor model are too time consuming and numerically expansive and thus no option during the design process in an industrial environment. In contrast to the prediction of the performance, the determination of the surge limit with any numerical method with high accuracy is still an unsolved challenge. Various recent publications and several numerical and experimental investigations of the authors undertaken at Hochschule RheinMain and TU Darmstadt confirmed exactly this.Since the extensive work of Greitzer and many other researchers in this field, it is well known that surge is a time-dependent as well as a system dependent phenomena. It has been clearly shown for axial as well as for circumferential compressors, that for example the compressor exit plenum volume has a significant influence on the surge limit. In case of steady-state simulations, both characteristics are not modelled. The flow path starts close to the compressor inlet and ends at the volute outlet in most cases. This simply implies that there is no system information included in the model and therefore, there can be no surge limit. This has been clearly shown by experiments.Previous investigations of the authors of this paper showed, that it is possible to simulate some kind of an extended compressor map with steady-state simulations. This as well as experiments again confirmed, that the often-used numerical stability limit is no good indicator for the compressor surge limit. To overcome this issue, an enhanced Greitzer surge model should be used. This model should act as a link between the simulation and the system in which the compressor will be operated.The focus of this paper will rather be on the methodology of determining the surge limit than on the Greitzer model. The extended compressor map determined by steady-state simulations as well as the surge limit will be validated by experimental data of multiple different systems (different piping, pressure losses, etc.). Furthermore, important parameters influencing the quality of the determined surge limit will be shown.