軸流ファンからの空力音の共鳴管を用いた制御に関する実験的研究

抄録

Small axial fans are widely used for cooling electronic devices, where the installation of fans in a small space such as a narrow duct can lead to the radiation of intense aerodynamic noise. The methods for reducing the aerodynamic noise from the axial fans are necessary to be established. As a one of noise reduction technique, a resonator-type silencer to an axial fan is focused on. The objective of this study is to evaluate the effects of the resonator on the acoustic radiation from a small axial fan installed in a narrow duct. The narrow-band tones at the blade passing frequency, its harmonic frequencies and the first harmonic frequency of rotational number of the fan were observed from the fan without a resonator. The control effects of a resonant tube with adjustable depth installed in the fan casing on the acoustic radiation were investigated. As a result, the acoustic radiation were weakened at the blade passing frequency and its first harmonic frequency for different resonator depths. The resonance frequencies of the three-quarter- and one-quarter-wavelength modes of the resonator with these depths agreed with the blade passing frequency and its first harmonic frequency, respectively. Meanwhile, these tones were often intensified with other resonator depths. For the acoustic radiation at the frequency of the first harmonic frequency of the rotational number, sound reduction effects were obtained over a wide range of resonator depth, where the frequency did not match the resonance frequencies of the resonator.