Study on Design Method Considered Circulation Flow and Low Flow Rate Characteristics of a Centrifugal Blower Casing

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Flow in a blower casing which has no diffuser and large tongue clearance was studied. The following conclusions were obtained.(1) Pressure recovery in the casing, at the design point, was 45 percent in the scroll. The remaining 55 percent was recovered in the section between the scroll end and exit duct.(2) The section between the scroll end and exit duct acts as a high-performance diffuser. Centrifugal force produced by secondary flow and boundary layer suction are the main cause of high pressure recovery.(3) At the inlet of the exit duct, where the pressure suddenly rose, a reverse flow occurred on the shroud side wall of the casing and the upper part of the scroll wall at the flow rate Q/Q_d=O.61. This separation zone grew with decreasing flow rate.(4) Flow conditions in the section from the scroll end to the exit duct closely related to the low flow rate characteristics of the blower.