The effect of the radial vane diffuser fillet on single-stage centrifugal compressor performance was studied.It was shown that when the radii of fillets were relatively small

the effect of the fillet can be negligible.Then further increasing the radius of the fillet

the mass flow at choke decreased and the performance of the compressor started to deteriorate.Upon these results

the investigation of optimizing the compressor aerodynamic performance by modifying the structure of the fillets was performed.Therefore

the fillet structure with no fillet or small fillets on suction side which can prevent blockage and radius-changing fillets on pressure side which can reduce or remove the separation zone on pressure surface was proposed.As a result

the performance of the compressor was improved obviously by using this structure.Besides

separated effects of fillets in casing and hub on single stage performance were discussed.It was revealed that the fillets near the hub played the major role in performance optimization.