Effects of vaneless region length on the performance of centrifugal compressor with vaned diffuser

Effects of vaneless region length on the performance of a centrifugal compressor with vaned diffuser are studied in this paper. The vaneless region is defined as the space between the impeller outlet and the vaned diffuser inlet. In this work, the studied ratio between the diffuser inlet and impeller outlet is from 1.06 to 1.20. The simulation results show that the variation in the vaneless region has a great impact on the performance of the compressor stage. It is found that the proper extension of vaneless region improves the performance of compressor stage by significantly reducing the separation near shroud and uniformly disturbing flow velocity at impeller outlet and diffuser inlet. Sufficient extension of the vaneless region is necessary to produce beneficial effects, while the excessive extension will instead deteriorate the compressor performance. The mechanism of performance improvement is that reasonable vaneless space length is able to constrain the flow separation and to make the flow more uniform in the diffuser.