Study of the flow characteristics in multi-row vaned diffusers of a centrifugal compressor stage

The vaned diffuser has a significant impact on the performance and operating range of a centrifugal compressor stage, and multi-row vaned diffusers are applied to improve the compressor characteristics in this article. In order to validate the effectiveness of the present calculation method, the calculation results of the centrifugal compressor with the conventional diffuser have been verified by the experimental data. The simulation results reveal that, compared with the original model at design point, the isentropic efficiency increases by 2.8% and 4.1%, and the total pressure ratio increases by 1.9% and 3.4%, for the compressor stage with the two-row vaned diffuser and the three-row vaned diffuser, respectively. The models with multi-row vaned diffusers also give higher static pressure recovery coefficient and lower total pressure loss coefficient. A pressure gradient formed on vane suction surface near vane leading edge develops the flow separation in the conventional diffuser. The pressure gradient thus causes the secondary flow from hub to shroud on vane suction surface, aggravating the separation in the rear part of the conventional diffuser. The analysis of flow characteristics in diffuser passages also shows that using multi-row vaned diffusers can alleviate flow separation appearing in the diffuser passages.