Aerodynamic performance optimization and unsteady flow field stability analysis of a supercritical carbon dioxide centrifugal compressor with non-uniform blade tip clearance

Tip leakage flow is a critical factor constraining the efficiency and stability of supercritical carbon dioxide (SCO2) centrifugal compressors. To address this challenge, this study proposes a non-uniform blade tip clearance design and establishes a parametric closed-loop optimization framework based on the NSGA-III algorithm to investigate its aerodynamic performance enhancement and unsteady flow dissipation suppression mechanisms. The results demonstrate that the optimized non-uniform clearance configuration significantly improves compressor performance, increasing the pressure ratio and isentropic efficiency by 3.55% and 5.65%, respectively, at the design point. Unsteady flow analysis reveals that the non-uniform clearance actively modulates the pressure gradient distribution in the tip region, effectively suppressing the scale and intensity of the tip leakage vortex and weakening the shear mixing between the leakage flow and the main flow. Consequently, the turbulent kinetic energy dissipation rate in the diffuser region is reduced by 33.08%. Entropy generation analysis further confirms a substantial reduction in irreversible energy losses in the tip region, with the average entropy generation rate at 0.9 BH (Blade Height) decreasing by 46.78%. Furthermore, the area-weighted average turbulent kinetic energy on the S1 stream surface is reduced by 10.4% globally, indicating a comprehensive improvement in flow stability. This study elucidates the physical mechanism by which non-uniform blade tip clearance enhances SCO2 compressor performance through flow structure reconstruction, providing a new theoretical basis and optimization pathway for high-performance turbomachinery design.