Effect of Diffuser Inlet Velocity Distribution on Rotating Stall Inception of a Centrifugal Blower

The effect of diffuser inlet velocity distribution on unstable flow inception was examined experimentally in the vaneless diffuser of a centrifugal blower with the backswept blade impeller. In order to suppress the reverse flow appeared firstly on the hub side wall at small flow rates, the velocity was increased locally near the hub side of the diffuser inlet. As a result, the flow rate of rotating stall inception was decreased and the stall margin was improved. It is found that the rotating stall in the vaneless diffuser is mainly caused by the 3-D boundary layer separation on the hub side wall not on the shroud wall