Self-recirculation casing treatment can significantly improve the aerodynamic performance of the supercritical carbon dioxide centrifugal impeller in small flow rate region

but the improvement is not obvious near the large flow rate region. Therefore

the coupling effect between the self-recirculation casing treatment and the key parameter of the impeller is considered

and the coupling optimization of the casing treatment geometry and the impeller blade sweep angle is carried out to achieve a comprehensive improvement of the impeller performance.After the coupling optimization

the efficiency of the impeller is increased by 3.51%

2.60% and 4.43% respectively under the large flow rate condition

the design condition and the small flow rate condition. The mechanisms of the coupling optimization for stability and efficiency enhancements are as follows. Under the large flow rate condition

the flow incidence angle of impeller is improved

the subcritical zone inside the impeller is reduced

then the condensation is suppressed and the flow capacity of the impeller is improved. Under the design condition

the recirculation flow of casing treatment is increased

more low-energy fluid near the shroud tip is removed

and the flow field structure downstream of the impeller is improved. Under the small flow rate condition

the internal blockage of the impeller is effectively reduced

the flow stability of the impeller is enhanced

and the mixing loss caused by the recirculation flow is improved

so the impeller efficiency is improved.