IDR: Phononic Surfaces for Flow Control

这个跨学科的研究项目提出了一个与流体相互作用的新概念——柔性表面可以被设计成水弹性或气弹性与边界层流动以有利的方式相互作用，从而减少阻力。受凝聚态物理的启发，其基本思想是在表面的内核处有一个周期性的晶格结构，因此被称为声子表面。表面的设计主要是为了延迟层流到湍流的过渡和分离，同时也为了减少完全发展的湍流的阻力。其他可以同时实现的功能是减少整体振动和结构噪声发射。研究计划包括对所提出的声子表面的建模、分析和设计进行有效、系统和集成的方法研究。对于周期性晶格单元胞带结构的计算，将采用一种新颖有效的基于模态分析的计算方案。将为单元优化创建专门的遗传算法算子。直接数值模拟流动和弹性波动在表面将进行。单元格设计将独立于完全耦合的固体-流体模拟进行，从而节省了大量的计算量。研究的跨学科性质，在动力系统，凝聚态物理和流体动力学的十字路口将丰富计划研究的各个方面。阐明固体表面内和表面下的色散周期波与非线性不稳定流体波之间相互作用的性质，将构成涉及基本物理现象的新发现。对这一知识的后续利用有望为流动控制开辟一个新的方向。就流线型船舶、飞机或一般车辆而言，建议的减阻概念将大大提高燃油效率，从而带来经济和环境效益。不同类型的涡轮机性能的提高也可以实现。

This Interdisciplinary Research project presents a new concept for surfaces interacting with fluids - flexible surfaces that can be designed to hydroelastically or aeroelastically interact with boundary-layer flow in a favorable manner leading to reduction of drag forces. The basic idea, which is inspired by condensed matter physics, is to have a periodic lattice structure at the inner core of the surface, hence the phrase phononic surface. The surface will be primarily designed to delay laminar-to-turbulence transition and separation, and also to cause drag reduction for fully developed turbulent flow. Other functions that can be simultaneously realized are reduction of overall vibrations and structural noise emission. The research plan involves investigation of an efficient, systematic and integrated methodology for modeling, analysis and design of the proposed phononic surfaces. For the periodic lattice unit cell band structure calculation, a novel and efficient computational scheme based on modal analysis will be utilized. Specialized genetic algorithm operators will be created for the unit cell optimization. Direct numerical simulation of the flow and the elastic wave motion in the surface will be carried out. The unit-cell design will be performed independently of the full coupled solid-fluid simulations thus providing crucial computational savings. The interdisciplinary nature of the research, at the cross-roads of dynamical systems, condensed matter physics and fluid dynamics will enrich the various aspects of the planned research. Elucidating the nature of the interaction between the dispersive periodic waves in and beneath the solid surface and the nonlinear and unstable fluid waves will constitute a new discovery involving fundamental physical phenomena. The subsequent utilization of this knowledge promises to open a new direction in flow control. For streamlined ships and aircrafts, or vehicles in general, the proposed drag-reduction concept will bring about substantial improvements in fuel efficiency and hence economic and environmental benefits. Gains to the performance of turbines of different sorts could also be realized.