Thermodynamic investigation of the secondary flow inside centrifugal compressor for compressed air energy storage based on local dissipation

Centrifugal compressors are critical components of compressed air energy storage (CAES) systems and are of great interest to understanding internal secondary flows and their resulting energy losses. While previous studies have primarily described these secondary flows using empirical correlation equations, this paper conducts nu-merical simulations of a high-loading centrifugal compressor after performing an experimental validation. The changes in the secondary flow structure in the impeller are analyzed for different operating conditions using a specific identification method based on the simulation results. The local dissipation coefficient is used as a weighting to analyze the enthalpy losses due to different sources during the impeller's thermodynamic process. The variations of the loss proportions from different sources with the dimensionless operating parameters (flow coefficient, impeller machine Mach number, and loading coefficient) are discussed. The reasons for the trends of different loss types correlate with the flow structure, and three different loss regions in the whole operation range are distinguished. The energy loss inside an optimized impeller is compared with the baseline, and the results demonstrate that different losses can be controlled by adjusting the secondary flow structure within the impeller. This study provides a reference for enhancing the understanding of thermodynamic processes within a centrif-ugal impeller and aims to further the development of advanced centrifugal compressors.