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

表面的湍流可能会限制声纳系统的探测性能。该项目将研究表面图案在降低暴露在湍流中的结构中流动噪声方面的有效性，将流体力学、水声学和结构动力学的学科结合起来，以确定表面下传感器的噪声响应。流动诱导噪声是影响声纳系统性能的限制因素，包括船载和拖曳阵列声纳。在一个典型的系统中，通过在流体和传感器之间引入隔离层来减弱由湍流引起的表面压力波动所产生的水声噪声的影响，通过该隔离层可以衰减非传播模式。这里的目的是通过解决湍流压力波动的产生及其传播到阵列中的根本问题来减小阵列体积，在保持或改进当前性能的同时允许减小尺寸。我们将通过以下几种机制来研究超表面如何影响传感器上的流动噪声的变化来实现这一目标：(I)通过表面图案化来减少阻力，这可能导致表面湍流压力变化的减少；(Ii)图案化导致在湍流边界层中产生的波数的改变；(Iii)使用共振亚表面来控制结构波的传播，增加了流噪声可以被引导离开传感元件或耦合到更高衰减模式的可能性。到目前为止，超材料在水下世界中还没有得到充分的开发，该项目将为科学界和工程界提供宝贵的信息。

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.