Numerical study of the reynolds number on the energy losses inside centrifugal compressor

Abstract

The increasing demand for more efficient energy conversion is making it extremely difficult for designers to develop next generation of centrifugal compressors. As the Reynolds number in centrifugal compressor operation decreases with increasing flight altitude, the efficiency degradation associated with it has been a key limitation to the energy conversion efficiency of aircraft engines. In this paper, the performance and internal flow field of a centrifugal compressor for a rear stage of a combined compressor are numerically simulated under different inlet conditions. The sources of efficiency degradation under low Reynolds numbers are discussed. Under low Reynolds numbers, the thermodynamic process in the compressor deviates more and more from the isentropic process. By establishing a way to classify different types of energy losses, the variation of different types of losses inside the impeller and diffuser are compared under different Renolds number. The results show that, when the boundary layer loss in the impeller increases as Reynolds number decreases, the recirculation loss and secondary flow loss also increase, which leads to a more obvious performance degradation. On the contrary, in the diffuser, the energy loss originally dominated by the boundary layer loss and the main flow loss, after the Reynolds number decreases, the boundary layer loss becomes the only source.