On enhancing the noise-reduction performance of the acoustic lined duct utilizing the phase-modulating metasurface

Abstract

Abstract This work proposes a noise-reduction structure that integrate phase-modulating metasurface (PMM) with acoustic liners (ALs) to enhance the absorption performance of a duct with relatively small length-diameter ratio. The PMM manipulate the wavefront by introducing different transmission phase shifts, so that the spinning wave within the duct is generated. Compared with the plane wave, the generated spinning wave has a lower group velocity, which results in a greater traveling distance over the ALs in the duct. The optimization design is performed to determine the final structural parameters of the PMM, which is based on the predictions of the amplitude and phase shift of the acoustic wave at the outlet of the PMM using the theory of metascreen-based acoustic passive phased array. With the manipulation of the PMM, the incident plane wave is modulated into a spinning wave, and then enters into the ALD, whose structural parameters are optimized by maximizing the transmission loss using the mode-matching technique. Finally, the noise-reduction performance of this combined structure is evaluated by numerical simulations. The results demonstrate that, compared with the traditional ALD, the proposed structure exhibits a 83.8% increase in transmission loss, and hence the noise-reduction performance is significantly improved.