Numerical study on the performance and internal flow of centrifugal impeller under external cooling conditions

In the process of gas compression within a centrifugal compressor, the temperature of the gas within the impeller rises, lead ing to deformation of the impeller and, even, instability. To ensure the stability of the impeller during operation, cooling the impeller is necessary. Based on the Krain centrifugal compressor, this study employs the finite volume method for the numerical resolution of the impeller's single flow passage, to examine the performance of the impeller under various external cooling conditions. Furthermore, the internal flow of the impeller is analyzed using entropy generation analysis. The results indicate that under external cooling conditions, the compressor's total pressure ratio and polytropic efficiency bear a linear relationship with the wall heat flux; an increase in wall heat flux leads to an improvement in the total pressure ratio and polytropic efficiency. The enhancement of impeller performance correlates well with the decrease in local entropy generation rate caused by heat transfer and temperature fluctuations. This performance enhancement is primarily concentrated at the blade tip of the impeller outlet, due to high gas temperatures near the impeller outlet, which result in substantial wall heat flux and a significant reduction in flow losses induced by heat transfer and temperature fluctuations.