Effects of tip clearance and inlet temperature on flow instability in a supercritical CO₂ centrifugal compressor near stall

Centrifugal compressors are widely employed in supercritical carbon dioxide (sCO₂) Brayton cycles due to their compact structure and high-power density. However, as the operating condition approaches the critical point of CO₂ (304.13 K, 7.38 MPa), maintaining compressor stability becomes a major challenge. In this study, numerical simulations are conducted to investigate the effects of blade tip clearance and inlet temperature on centrifugal compressor stall near the stall margin. The results show that as the tip clearance increases from 0.3 mm to 0.6 mm, the maximum vorticity magnitude increases from 1.346 × 10 6 s −1 to 1.689 × 10 6 s −1 , indicating significant intensification of the tip leakage vortex, while the tip clearance loss coefficient rises from 0.110 to 0.260. The continued growth of these vortices eventually spreads across the entire flow passage, triggering stall. The formation of these vortices elevates the local temperature and pressure near the leading edge, thereby suppressing condensation, with the corresponding liquid mass fraction decreasing from 1.15% to 0.73%. This reveals a dual competitive mechanism between flow deterioration and phase-change suppression. Quantitative analysis demonstrates that flow deterioration plays a dominant role in determining compressor stability. Furthermore, lowering the inlet temperature from 310 K to 305 K enhances the pressure ratio and overall performance, but intensifies condensation at the leading edge, reducing stability and increasing stall risk.