Performance optimization mechanisms in a supercritical carbon dioxide centrifugal compressor with micro-blades

The supercritical carbon dioxide (sCO2) centrifugal compressor, as a core component of the Brayton power cycle, faces a critical technical challenge in expanding its stable operating range to ensure stable operation of the cycle system. This investigation was conducted on a sCO2 centrifugal compressor to quantify the effects of the micro-blade on the performance and stability of the centrifugal compressor. The results demonstrate that adding the micro-blade profiles on the shroud side of the vaneless diffuser extends the compressor's stable operating range by 7.76%. The stability enhancement mechanism of the micro-blade primarily manifests in three aspects: first, after adding the micro-blade, the reverse flow region on the shroud side of the original diffuser is effectively truncated, reducing the reverse flow region on the shroud side. Second, on the pressure surface of the micro-blade, the airflow experiences counterclockwise circumferential deflection due to physical blockage from the micro-blade and moves toward the outlet of the diffuser under the action of the inlet vortex, which reduces the flow blockage. Third, low-energy fluid near the micro-blade forms a channel vortex and wake vortex that promote mixing between the main flow and low-energy fluid in the reverse flow region, enhancing the momentum of the low-energy fluid and strengthening its ability to resist adverse pressure gradients. The synergy of these effects reduces the accumulation of low-energy fluid on the shroud side of diffuser, improves the flow conditions in the diffuser passage, and consequently delays stall inception.