Reflected wave manipulation by acoustic metasurface in a grazing shear flow

Qu, Renhao, Guo, Jingwen, Fang, Yi, Yi, Wei, Zhong, Siyang, Angland, David and Zhang, Xin (2022) Reflected wave manipulation by acoustic metasurface in a grazing shear flow. In 28th AIAA/CEAS Aeroacoustics Conference, 2022. American Institute of Aeronautics and Astronautics.. (doi:10.2514/6.2022-2905).

Abstract

Acoustic metasurfaces (AMs) are artificial structures that can realize exotic properties, such as negative refraction and perfect absorption, etc., in sub-wavelength thickness scales. Most of the previous studies on AMs were conducted in laboratory conditions with a static medium, limiting their applications in practical conditions, e.g., the aircraft engines where an aerodynamic background flow is present. To fill this gap, the effect of a grazing shear flow on the reflection performance of AMs with periodic construction is studied. An AMs design method is proposed to realize effective wavefront manipulation with the consideration of the shear flow. The strategy is to form a linear reflected phase-shifting covering 0 to 2π at the interference plane between the uniform and the shear flow regions. To validate the effectiveness of the proposed design method, two acoustic porous metasurfaces (APMs), APM1 for the uniform flow and APM2 for the shear flow, are designed and their reflection characteristics are numerically investigated. Results show that the presence of the shear layer deteriorates the effectiveness of APM1 under oblique incidences due to the considerable refraction effect. In contrast, APM2 realizes reflection wavefront manipulation, such as anomalous reflection and surface wave conversion, under the same conditions. This study provides a guideline for AMs design in flow conditions, which offers potential for noise control in aeroacoustic problems.

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Contributors

Author: David Angland

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