The proposal of active noise control method for the same phase sources distributed on the circle from the rotational blade and the index of the attenuation level

Abstract

In this paper, we propose the active noise control method for the same phase sources distributed on the circle. These sources, which have zero lobe mode, is radiate from the duct fan without attenuation in the duct. Therefore, noise control is need for these sources, which have zero lobe mode. At first, we propose the first ANC method with two control speakers set outside of the duct. This method assume the virtual sound source, which imitate the same phase sources distributed on the circle, is set on the center of the duct edge. We verify this assumption is proper for the same phase sources distributed on the circle with the numerical simulation. Second, we propose the second ANC method with more than three control speakers, which imitate the characteristic of the same phase sources distributed on the circle correctly to improve the attenuation effect. Moreover, we propose the index of the attenuation level. The numerical simulation confirms the validity of the proposed index for the second ANC method. In addition, we verified the attenuation effect of the second ANC method is higher than the first ANC method. The points of these methods to attenuate zero lobe mode are the number of the control speakers are less than conventional method and control speakers are set outside of the duct with considering the sound power attenuation.