Design of a rotating hole-type sonic crystal structure for low-frequency noise reduction

The characteristics of a kind of rotating hole-type sonic crystal(or phononic crystal) which can be designed to reduce low-frequency noise are discussed in this paper based on the experiment results. In the experiment, a kind of two-dimensional sonic crystal(SC) was applied to reduce the rotating structure noise in 0-2550Hz obviously and the maximum value of noise reduction reaches 25dB.This phenomenon couldn´t be explained by the static model analysis. Therefore, a proper theoretical model is built to describe the impact of the interaction between rotating sonic crystal and the air around it. Dispersion relation of this equivalent model is obtained, which shows that the wave couldn´t propagate in the range of 0-5400Hz. This phenomenon illustrates that the approximate band gap feature is existed in the low-frequency range. This kind of extremely low-frequency band gap is due to the combination of the vibration of a single air scatter and the interaction among scatters which are generated by the SC motion. Theoretical result fits the experiment data well. In general, for rotating machine noise control in low-frequency range, the wave propagation impediment phenomenon which is generated by SC structure rotating could be expected to be of great interest technically.