The uses of tandem inducers has been proposed in the past in an attempt to reduce the inducer shock losses and to improve the performance and operating range of centrifugal compressors. However throughout the literature the benefits/penalties of this type of compressor design are still unclear, with contradictory conclusions and very few studies attempting to understand the causes of the observed benefits/penalties. Additionally none of the cases reported for centrifugal compressors has looked into the impact of overlap between the inducer and the main blade. The current study looks into the different aspects of the design of centrifugal compressors with tandem inducers and their effect on the performance of a high flow coefficient, high pressure ratio centrifugal compressor. Aspects such as clocking, axial gap between the inducer and the compressor main blade, axial overlap, and the performance in combination with a vaned diffuser are discussed. Overall the results indicate that it is possible to design centrifugal compressors with tandem inducers that provide similar or even a slight performance benefit at design point, and that tandem inducers can provide significant performance benefits at off design conditions by improving the flow conditions along the main blade suction side, and by improving the inlet conditions to a vaned diffuser. The results also indicate that the impact of the axial gap between the inducer and the main blade has little impact on the compressor performance, that clocking will have a significant impact on the performance of the compressor and that the best performance will be obtained when the tandem inducer is almost aligned with the main blade of the compressor, since this avoids the blockage and losses incurred by other clocking arrangements.

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