Aerodynamic collaborative design of high-temperature heat pump centrifugal compressor based on the matching of impeller geometry and real gas effects

Large-scale centrifugal compressors using organic fluids serve as core components in high-temperature industrial heat pump systems. Their aerodynamic performance significantly impacts the efficiency and operational stability of the heat pump system. However, the pronounced real gas effects of organic fluids challenge the applicability of conventional design theories. This study conducted a numerical investigation on an MW-scale R245fa centrifugal impeller, identifying a mismatch between the throughflow area distribution and the nonlinear density variation under high-temperature heat pump operating conditions. Under the low speed of sound and real gas thermophysical conditions of R245fa, this mismatch is associated with aerodynamic choking near the impeller inducer, as well as diffusion separation in the rear passage. Subsequently, the distinct roles of the meridional contour, leading edge profiles, and relative outlet width in regulating the throughflow area were investigated. Based on these findings, a multi-parameter collaborative optimization was executed, yielding an optimized configuration that integrates a “front-expansion and rear-contraction” S-shaped meridional contour, a high-axial-ratio elliptical leading edge, and a reduced relative outlet width. The results demonstrate that the optimized impeller achieves a 1.99% increase in isentropic efficiency at the design point and a significant 34.33% broadening of its stable operating range. Meanwhile, “throughflow area–fluid density matching” is an important factor affecting the internal flow organization and aerodynamic performance of the investigated R245fa high-temperature heat-pump impeller.