Flow instability suppression and deep surge delay by non-axisymmetric vaned diffuser in a centrifugal compressor

The performance of centrifugal compressors is significantly limited by the deep surge with strong flow oscillations, and the occurrence of deep surge is found to be related to flow instabilities. A novel in-house designed non-axisymmetric vaned diffuser (NAVD) is applied in a centrifugal compressor, and this paper experimentally analyzes influences of the NAVD on suppressing the flow instability and delaying the deep surge. Results show that the flow instability at the diffuser inlet region are distinctly suppressed by the NAVD, meanwhile the deep surge is delayed at 90% speed which extends the stable flow range (SFR) by 25.0%. Nevertheless, the NAVD neither delays the deep surge at other rotating speeds, nor does it suppress the flow instability at the impeller inlet region. According to a previous research, only at 90% speed, the deep surge onset initiates from the diffuser inlet flow instability, and this explains why the NAVD fails to delay the deep surge occurrence at other rotating speeds except for 90% speed. This paper experimentally proves that the NAVD has a positive influence on the flow instability suppression and deep surge delay in some situations, and it provides a new method to improve the compressor stability by non-axisymmetric vaned diffuser. (C) 2019 Elsevier Masson SAS. All rights reserved.