Active cancellation of higher-order blade-passing frequency noise radiated from a centrifugal blower

Active cancellation of noise source of higher-order blade-passing frequency noise, abbreviated to BPF noise, radiated from a centrifugal blower is conducted. The extents of noise sources of 2nd- and 3rd-order BPF components were determined by measuring a cross-correlation function between the data of the acoustic pressure measured at blower inlet and the pressure fluctuation on the scroll surface. The effective noise sources of these higher-order BPF components exist on the volute side surface of scroll relatively apart from the cut off apex, and vary irregularly with operating conditions of the blower. While the noise source of fundamental BPF lies on the vicinity of the cut off apex as usually expected. Oscillating the volute side surface of the cut off, i.e. the effective noise source of higher-order BPF components, directly by piezoelectric actuators, sound pressure level of higher-order BPF components can be reduced more than 15 decibels, and discrete tone disappears completely from power spectra of the blower radiated noise.