A centrifugal compressor stage has been investigated mainly experimentally for aerodynamic stage optimization. The rotor consists of a separate inducer with 14 blades and an impeller with 28 blades. Both rotor components can be locked with each other at different circumferential positions thus, forming either a conventional splitter blade rotor or a tandem bladed rotor of adjustable geometry. The influence of the tandem blade geometry on the rotor and stage characteristics is studied in detail. Laser-2-Focus-System measurements were performed at nine locations all over the rotor taking three different circumferential inducer positions into account. The improvement with the tandem blade configuration on the rotor and stage characteristics is small but significant differences in the flow field of the two different impeller channels in the rear and exit part of the rotor are recognizable. The velocity differences of the jet/wake flow are reduced by using tandem blades which lead to a slight increased stage pressure ratio and surge margin.

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