We report a numerical study on the vaneless diffuser core flowinstability in centrifugal compressors. The analysis is performedfor the purpose of better understanding of the rotating stall flowmechanism in radial vaneless diffusers. Since the analysis isrestricted to the two-dimensional core flow, the effect of the wallboundary layers is neglected. A commercial code with the standardincompressible viscous flow solver is applied to model thevaneless diffuser core flow in the plane parallel to the diffuserwalls. At the diffuser inlet, rotating jet-wake velocity patternis prescribed and at the diffuser outlet constant static pressureis assumed. Under these circumstances, two-dimensional rotatingflow instability similar to rotating stall is found to exist.Performed parameter analysis reveals that this instability isstrongly influenced by the diffuser geometry and the inlet andoutlet flow conditions.
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