Return channel loss reduction in multi-stage centrifugal compressors

Abstract

This thesis presents concepts for improving the performance of return channels in multi-stage centrifugal compressors. Geometries have been developed to reduce both separation and viscous losses. A number of different features with potential to reduce separation have also been investigated. The final proposed geometry uses a vaneless diffuser which narrows on the shroud side at the beginning of the 180' bend, an axially extended 1800 bend with increasing radius of curvature, and return channel vane leading edge radial position at an increased radius compared to the baseline. Three-dimensional calculations showed a 9% loss reduction compared to previous work [1], with a cumulative loss reduction of 19% compared to a baseline geometry. The geometry developed was based on specified inlet conditions. To examine the potential for increased performance if this constraint was removed, a return channel geometry was also defined that incorporated the same features but allowed modified inlet conditions, specifically radial inlet flow. The design of the impeller required for this new inlet flow was not considered. An overall loss reduction of 23% compared to baseline was found from the calculations. Modification of the impeller geometry is thus proposed as future work.