Aerodynamic Analysis of Return Channels of Multi-Stage Centrifugal Compressors

Abstract

Abstract From the wide range of applications in which centrifugal compressors are used, two different return channels will be investigated, to demonstrate the influence of flow coefficients onto the flow structure. The investigated return channels are typical to join the exit from one stage of a centrifugal machine to the inlet of the next stage and cover the range of very small and large flow coefficients. Starting with a comparison between measurements and numerical results to demonstrate the performance of the calculations, the comparison of both return channels show that three-dimensional phenomena and viscous effects such as secondary flow and wakes have appreciable effect on the fluid dynamics and performance of centrifugal compressors. Especially the deceleration of the flow introduces large separations and recirculations which will decrease the efficiency. Furthermore, a variation of the 180°-bend demonstrates the influence of streamline curvature onto the separation behaviour within the whole return channel. Due to the strongly three-dimensional flow structure with high streamline curvature and secondary flows on hub and shroud of the return channel vanes, a modified explicit algebraic Reynolds stress model will be used for all calculations.