Effects of absorbing duct on turbulent noise of CR-fan

We made an experimental and theoretical investigations on turbulent noise reduction of the counter rotating axial flow fan. The fan had the absorbing systems which was consisted of the absorbing duct and iron duct partly. The absorption coefficient of the whole duct system was obtained in consideration of the respective absorption coefficient of the absorbing duct and iron duct. In this paper, it was examined the effects of three parameters, such as the length of absorbing duct, the arrangement of absorbing duct, and the thickness of the absorbing material, on the aerodynamic characteristics and the turbulent noise. Moreover, the comparison between the predicted and the measured values was tried for radiated noise from fan. The agreement between the predicted and measured values was satisfactory