Component matching and its role in the formation of two-regime surge in centrifugal compressors

Two-regime surge, a newly identified flow instability peculiar to centrifugal compressors, plagues the development of small and medium-sized aero-engines. This paper examines how component matching precipitates the onset of this systemic compression-system instability. Integrating theory and three-dimensional simulations with comprehensive experimental data, the evolution of flow instabilities of two-regime surge from individual components to the entire compression system is investigated. Results show that the compressor characteristic associated with two-regime surge is biquadratic, rather than the conventional quadratic, and exhibits two discrete slope reversals. The reversal, from positive to negative slope as mass flow decreases, re-energizes the compressor when it is on the verge of collapse and constitutes the necessary condition for the two-regime surge. Component stability analysis reveals that the impeller dominates this slope change, and the mechanism is the non-monotonic variation of the impeller incidence angle caused by tip-region backflow blockage. Subsequent parametric scrutiny quantifies how alternative component-matching strategies modulate the biquadratic characteristic. A benchmark compressor that is inherently free of two-regime surge is finally analyzed to corroborate the findings. The results furnish new insights into the genesis of this distinctive instability from the perspective of component matching.