The diffuser system of a centrifugal compressor comes basically in two general categories either as vaneless or vaned diffuser. Vaned diffusers can further be subdivided into two depending on channel geometry as straight channel or curved channel, or depending on solidity. Three different diffuser types: a vaneless, conventional vaned and a low solidity vaned were tested in the present study. All diffusers were tested downstream of the same impeller. All the diffusers had the same diffuser exit radius to impeller tip radius ratio.

The influence of each type of diffuser on the performance and stall characteristics of the inducer and impeller as a whole was studied. In addition, diffuser stall characteristics of each type diffuser were also studied. The type of diffuser had no significant effect on inducer and impeller stall. The inducer was more stable with the conventional vaned diffuser configuration. Rotating Stall was detected with the vaneless diffuser configuration at the onset of surge. Four stall cells rotated in the same direction as the impeller at 122 Hz.

Numerous works have been documented on rotating stall and surge for centrifugal compressors. Prediction of the inception of rotating stall and surge for a specific geometry and operation is not yet fully possible. Therefore, experimental results and correlations are still of great importance.

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