多翼ファンの空力音源に及ぼす舌部隙間流れの影響

概要

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A visualization method of aerodynamic noise source based on momentum in wake of a centrifugal impeller is proposed. The characteristics of the fan noise operated at the design point and the off design point are discussed by the visualization. When the flow rate changed from the design point to the off design point, the overall noise level of the fan has increased by 3 dB (A) because of the broadband noise. According to the visualization of aerodynamic noise source proposed by this study, it clarified that the domain of the flow related to the fan noise exists at the vicinity of the volute tongue. Since the flow almost flows out to the exit of the fan at the off-design, the large difference of the momentum in the wake occurred at the vicinity of the volute tongue. It is shown that the flow pattern at the vicinity of the volute tongue is one of the reasons for increasing of the fan noise.