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The vaned diffuser plays a key role in the performance of a centrifugal compressor stage.Different vaned diffusers have been invented and designed in the past to improve the characteristics of the centrifugal compressor stage.In this paper,a new two-row vaned diffuser is proposed.The two-row vaned diffuser has a large space between the two rows,while the tandem vaned diffuser has its two-row vanes placed closely in the radial direction and has a gap between the two-row vanes.To verify the improvement effect of the two-row vaned diffuser on the performance of the centrifugal compressor,the flow field in a centrifugal compressor impeller and its vane diffuser were analyzed by using numerical simulation.Based on the flow fields,the original arc-vaned diffuser was replaced by the two-row vaned diffuser.The first row of the new vaned diffuser is the same as the first half of original arc-vaned diffuser,while the second row that is placed 0.3 chords downstream of the first row was re-designed according to the simulated flow fields.The numerical simulation reveals that the stage polytropic efficiency is improved by 2.4%while the pressure ratio rises by 1.8%,with a wider stable operation range.The improvement mechanism for such a performance enhancement is that in the second half of the diffuser passage the flow usually has a tendency to separate due to a large diffusion effect.By contrast,the large radial space between the two row vanes of the new diffuser has a tendency to make the chaos flow more uniform,and thus improves the inlet flow of the second row vane.As a result,the overall performance of the centrifugal compressor stage is enhanced evidently.