Control of Flow-Induced Near-field Noise Through the use of Metasurfaces

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Turbulent flow over a surface may limit the detection performance of sonar systems. This project will investigate the effectiveness of patterned surfaces in the reduction of flow noise in structures exposed to turbulent flow, bringing together the disciplines of hydrodynamics, hydroacoustics, and structural dynamics to determine the noise response of a sensor beneath the surface.Flow-induced noise is a limiting factor affecting the performance of sonar systems, including both hull-mounted and towed array sonars. In a typical system, the impact of hydro acoustic noise generated by turbulence - induced pressure fluctuations at the surface is mitigated by the introduction of a stand-off layer between the flow and the sensor, through which non-propagating modes are attenuated. The aim here is to reduce array volume by tackling the fundamental problem of the generation of the turbulent pressure fluctuations and their propagation into the array, allowing size reductions whilst maintaining or improving on current performance. We will achieve this goal by investigating how metasurfaces may effect changes to the flow noise at a sensor through several mechanisms: (i) drag reduction through patterning of the surface, which may result in a reduction in turbulent pressure variations at the surface; (ii) patterning resulting in modification of the wavenumbers generated in the turbulent boundary layer; (iii) use of resonant metasurfaces to control the propagation of structural waves, raising the possibility that flow noise can be steered away from the sensing elements or coupled into more highly attenuated modes. To date, metamaterials have not been fully exploited in the underwater world, and this project will provide valuable information to the scientific and engineering communities.