The operating point of the centrifugal blower used in vacuum cleaners is not stable; dust particles in the air bag make the characteristics of the system steeper and steeper so that the operating point is slowly shifted towards a lower flow rate. In the case of centrifugal blowers with unstable characteristics the operation point also slips into an unstable region. The unstable region appears due to rotating stall created in the nozzle and in the rotor blade or guide vane channels. At some operating conditions the rotating stall causes the appearance of surge, representing the lowest region of blower operating stability. The rotating stall and surge do not depend on the speed of rotation; the rotating stall depends on the throttling, whereas the surge depends additionaly on the blower geometry; first of all, on the rotor inlet and outlet blade angle, and than on the existance of a vaned diffuser. Rotating stall and surge cause an increase in the emitted noise and a deterioration in performance of the blower. The present paper highlights the rotating stall and surge generation phenomena and their influence on the emitted noise using Euler's fundamental equation, noise spectra measurements and analysis of centrifugal blowers used in vacuum cleaners.
展开▼
