The effects of vaneless diffusers and vaned diffusers with different entrance installation angles on a centrifugal compressor basic stage were studied with numerical calculations and tests. For compressor basic stage with vaneless diffuser

inner flowfield characteristics at nearsurge point

design point

and nearchoke point were analyzed

showing that vortex existed in the inlet and outlet of impeller blade and back of reflux blade at nearsurge point while flow state was good at designpoint and nearchoke point; as for nearchoke point

friction resistance loss increased with large flow speed

causing stage efficiency drop quickly. For compressor basic stage with single arc vaned diffuser

the effects on surge margin

choke margin and efficiency were analyzed with five different vaned diffuser entrance installation angles. The results show that when entrance installation angle of vaned diffuser decreases 3 degrees than the design value while outlet installation angle is fixed

the polytropic efficiency and polytropic energetic coefficient of stage achieve the best value.