Influence of volute-induced distortion on the performance of a high-pressure-ratio centrifugal compressor with a vaneless diffuser for turbocharger applications

As the geometry of the volute of a turbocharger centrifugal compressor is non-axisymmetric, it causes a distortion at the outlet of the diffuser and influences the upstream components to make the distribution of the flow parameters non-axisymmetric. To quantify the circumferential distortion induced by the volute, a distortion model was proposed to replace the volute by imposing a circumferentially asymmetric pressure distribution. The simulation results prove that this model could reproduce the distortion induced by the volute and, therefore, was sufficient to allow research on the volute's effect. Based on the distortion model, variable amplitudes of distortion were realized, and the influence of the amplitude of the distortion on the performance of a centrifugal compressor was studied in detail. The results show that the distortion severely harms the aerodynamic stability of the compressor. Larger amplitude distortion cause worse compressor performance. The distortion induced by an asymmetric volute propagates to the upstream components and causes local flow separations in the diffuser and impeller, contributing to compressor surge. When the amplitude of the distortion increases up to 15%, the stable flow range of the compressor decreases 37.7%. The results provide useful guidelines to improve the performance of turbocharger compressors by decreasing the distortion induced by the asymmetric volute.