Pressure recovery in a centrifugal blower casing

The rate of circulating flow passing through the tongue division and the pressure recovery in the casing are investigated in a centrifugal blower, which has no diffuser and large tongue clearance. At the design point, the ratio of circulating flow rate to total flow rate at the scroll end is about 45 percent, and the pressure recovery in the scroll is about 45 percent. As the remaining 55 percent of the pressure recovery in the casing is recovered in the section between the scroll end and exit duct, this section acts as a high-performance diffuser. It is concluded that the centrifugal force produced by the secondary flow and boundary layer suction are the main causes of the large pressure recovery. Moreover, it is found that the flow conditions from the scroll toward the exit duct are closely related to the low flow rate characteristics of the blower.