Design of a low-frequency noise suppression periodic pipe and its acoustic performance test

To control the transmission of low-frequency noise in the ventilation and air conditioning pipelines, a periodic pipe equipped with a 1D array of Helmholtz mufflers was constructed. Such a periodic pipe has a set of screw holes distributed in the axial direction with identical spacing such that the Helmholtz mufflers could be seated into the holes via the matching screw on the Helmholtz neck, thereby forming periodic pipes with various lattice constants. Numerical simulation results show that there are two types of low-frequency band gaps existed in the periodic pipe system, i.e., the resonant and the Bragg type band gaps, respectively. These two types of gaps can be coupled by modulating the geometric parameters e.g., the lattice constant, via an exactly coupling condition. The experimental test of noise reduction (NR) and insertion loss (IL) further validate the theoretical prediction. Experimental results show that within the band gap frequency ranges, the propagation of acoustic waves in the periodic system will be prohibited, exhibiting a good suppression effect on the transmission of low-frequency pipe noise, particularly in the resonant gap frequency range. Moreover, increasing the installing space of Helmholtz mufflers, the Bragg type gap will be moved towards the lower frequency range. Under a certain condition, the Bragg and the resonant gaps could be combined together, giving rise to a low-frequency and broadband coupled gap with heavy attenuation effect. The experiment test reveals that the proposed strategy possesses a good control effect on the low-frequency noise transmission in the ventilation and air conditioning pipeline, thus providing a possible technical way to deal with the low-frequency noise problem in ship ventilation and air conditioning pipeline systems. © 2022, Editorial Office of Journal of Vibration and Shock. All right reserved.