Energy transfer and loss mechanisms of a centrifugal compressor stage in a high-altitude atmosphere

Existing research has established that high-altitude, low-Reynolds-number (low-Re) conditions cause deterioration in centrifugal compressor efficiency, pressure ratio, and operational stability; however, the aerodynamic matching between sub-components and the energy transfer and loss mechanisms within a centrifugal compressor stage under varying altitude conditions strongly depend on the stage configuration and operating condition. In this study, numerical simulations of flow in the High Efficiency Centrifugal Compressor (HECC) stage were conducted at altitudes ranging from 0 km to 10 km. The influence of altitude on stage and sub-component aerodynamic performance, energy transport characteristics, and loss mechanisms was examined. Results indicated that as altitude increased from 0 km to 10 km, the stage near-peak adiabatic efficiency decreased from 81.98% to 77.89%, while the stage total pressure ratio at peak efficiency increased from 4.60 to 6.16 due to the rise in corrected rotational speed. The Reynolds number decreased to approximately 42% of its sea-level value, enhancing viscous effects that thickened boundary layers and expanded the wake region at the impeller outlet. The total energy flux magnitude within the impeller decreased by more than half owing to reduced air density, while the local dissipation coefficient increased monotonically with altitude, with turbulent viscous dissipation identified as the dominant loss mechanism. The diffuser total pressure loss coefficient increased systematically with altitude, driven by the expansion of high-loss regions on the shroud side originating from intensified tip leakage flow interaction and endwall boundary layer thickening. The diffuser peak static pressure recovery coefficient remained approximately 0.66 across all altitudes, but the high-efficiency operating range narrowed considerably at high altitudes, indicating increased sensitivity to off-design conditions.