Numerical investigation of ?ow mechanisms of tandem impeller inside a centrifugal compressor

This study numerically investigated a single stage centrifugal compressor ‘‘Radiver'' with a wedge diffuser and several tandem-designed impellers to explore the ?ow phenomena within the tandem impeller and the potential to enhance compressor performance. The results demonstrate that tandem design and clocking fraction(ks) signi?cantly affects the compressor performance.The compressor stage with tandem impellers of Series A of boundary layer growth interruption alone are observed to have a widely operating range but ef?ciency and total pressure ratio penalty compared with that of conventional impeller. The tandem impeller with at least the same impeller ef?ciency as the conventional design is considered as a critical design criteria so that further modi?cation process based on the ?ow characteristic of tandem impeller is necessary. In order to restrain the inducer wake and exducer shock losses, parameters modi?cation of blade angle and thickness distributions are necessary and the modi?ed tandem impeller of Series B is obtained.The modi?ed tandem impeller with 25% clocking arrangement shows an 8.45% stall margin increase and maintains the total pressure ratio and ef?ciency as the conventional design, which proves the potential of tandem impeller to improve compressor stage performance. It is noteworthy that the tandem impellers of Radiver have not shown obviously balanced exit ?ow ?eld and the fundamental mechanism of stall margin extending of tandem impeller lies on the improved impeller/diffuser matching performance resulting from the incidence angle variation at diffuser inlet.