The supercritical CO2 gas turbine is considered to achieve a high cycle efficiency by reducing compressor work near the critical point. But test loops made by international community show that the performance of the compressor is still quite far from the target at the design point. The paper focuses on the influence of relative velocity ratio on the performances of centrifugal impellers operating with real gas CO2 and ideal gas CO2. At the same time, comparisons between characteristic curves of impellers operating at near critical, supercritical, and subcritical inlet condition with real gas CO2 are also demonstrated. Relative velocity ratio demonstrates the same trend with real and ideal gas CO2 in the same impeller, but the specific value is different. Impellers with real gas CO2 could achieve a high isentropic efficiency when relative velocity ratio is in the range of 1.05∼1.5. The results show that relative velocity ratio plays an important role in compressor performance.

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