EVALUATION AND PREDICTION OF BLADE PASSING FREQUENCY NOISE GENERATED BY A CENTRIFUGAL BLOWER

The blade-passing frequency noise, abbreviated to BPF noise, of a low- specific-speed centrifugal blower is analyzed by separating the freque ncy response of the transmission passage and the intensity of the nois e source. Frequency response has previously been evaluated by the auth ors using a one dimensional linear wave model, and the results have ag reed well with the experimental response in a practical range of the b lower speed. In the present study, the intensity of the noise source i s estimated by introducing the quasi-steady model of the blade wake im pingement on the scroll surface. The effective location of the noise s ource is determined by analyzing the cross-correlation between measure d data of the blower suction noise and pressure fluctuation on the scr oll surface. Then, the surface density distribution of a dipole noise source is determined from pressure fluctuation expressed in terms of q uasi-steady dynamic pressure of the traveling blade wake. Finally the free-field noise level is predicted by integrating the density spectru m of the noise source over the effective source area. The sound pressu re level of the blower suction noise is easily predicted by multiplyin g the free-field noise level by the frequency-response characteristics of the noise transmission passage.