Large Drag Reductions with Superhydrophobic Surfaces Sustainable in Turbulent Boundary Layer Flows

Kim，Chang-Jin 1336966利用最近开发的超疏水（SHPo）表面，即使在高速流动中也可以保持非润湿状态，加州大学洛杉矶分校的研究小组建议阐明它们如何在湍流中减少阻力（50%）。减阻的特点是实验和数值在很宽的雷诺数范围内的湍流边界层流动，这代表水上车辆的运动。开发的SHPo表面的最终效用将在海洋环境中的现场测试中得到证实。智力优点：尽管在过去的十年中对SHPo表面进行了大量的研究，但在获得可用于真实的应用的SHPo表面方面仍然存在挑战。尽管减阻是SHPo表面最有吸引力的特性，但在野外条件下（如室外水中），还没有任何表面表现出减阻效果。虽然减阻要求SHPo表面处于去湿状态作为必要条件，但去湿状态在水下非常脆弱。无论人们做什么，被困的气体最终都会扩散到周围的水中，最终使表面变湿。最近，PI的实验室通过开发一种半活性SHPo表面，即使在几十米深的水下也能保持去湿状态数月，从而大大提高了水下SHPo表面的鲁棒性。此外，他们在湍流边界层流动中的一些被动SHPo表面上获得了超过50%的减阻。即使在高速流动中，这些表面也被发现不湿润。在这些最新突破的推动下，加州大学洛杉矶分校的团队提出要在湍流中找到SHPo表面大减阻的基本物理原理，并在很宽的雷诺数范围内（5x 10 E5 - 2x 10 E7）建立减阻。最终，他们将证明在现场条件下的阻力减少，使用一艘小船。更广泛的影响：减少摩擦阻力的流动液体长期以来一直是一个难以捉摸的目标，在流体工程。 如果减阻是可持续的实用条件，仅节能就将带来显著的经济效益和环境效益。这项研究的目的是解释在代表大多数水上交通工具一般行驶条件的流动中，某些SHPo表面上的阻力是如何减少的。研究结果将通过实验室网站、杂志、博客和常规媒体广泛传播。研究成果将被整合到加州大学洛杉矶分校的课程和项目中，特别是博士学位。微机电系统和纳米技术的主要领域。此外，通过为非专业人员提供有吸引力的任务，该项目将促进本科生和高中生的教育。例如，本科生将通过加州大学洛杉矶分校工程学院的许多项目帮助开发现场测试设备。高中教师和学生可以在当地沿海水域帮助现场测试SHPo表面，加强加州大学洛杉矶分校加州纳米系统研究所（CNSI）的推广计划。

Kim, Chang-Jin1336966Utilizing recently developed superhydrophobic (SHPo) surfaces that can sustain the nonwetting state even in high-speed flows, the UCLA team proposes to elucidate how they experience such a reduced drag (by 50%) in turbulent flows. The drag reduction will be characterized both experimentally and numerically over a wide range of Reynolds numbers in turbulent boundary layer flows, which represent water vehicles in motion. The ultimate utility of the developed SHPo surfaces will be confirmed by the field tests in marine environment.Intellectual Merit :Despite numerous studies on SHPo surfaces over the past decade, challenges remain in obtaining SHPo surfaces deployable for real applications. Although drag reduction is the most attractive feature anticipated from the SHPo surfaces, no surface has ever demonstrated a drag reduction under a field condition, such as in outdoor water. While the drag reduction requires the SHPo surface to be in a dewetted state as a necessary condition,the dewetted state is very fragile underwater. No matter what one does, the trapped gas would eventually be diffused out to the surrounding water, eventually making the surface wetted. Recently the PI's lab has dramatically increased the robustness of underwater SHPo surfaces by developing a semi-active SHPo surface that sustained the dewetted state for month,) even in tens of meters of deth. In addition, they obtained over 50% drag reduction on some passive SHPo surfaces in turbulent boundary layer flows. These surfaces were also found nonwetting even in high-speed flows. Empowered by these recent breakthroughs, the UCLA team proposes to find the underlying physics of the large drag reduction on SHPo surfaces in turbulent flows, and establish the drag reduction over a wide range of Reynolds numbers (5x10E5 - 2x10E7). Ultimately, they would demonstrate a drag reduction under field conditions, using a small boat.Broader Impacts :Reduction of friction drag by flowing liquids has long been an elusive goal in fluid engineering. If the drag reduction is sustainable practical conditions, the energy savings alone will bring about significant benefits to the economy and the environment. Rhe proposed research aims to explain how drag is reduced on certain SHPo surfaces in flows that represent the general traveling conditions of most water vehicles. The results will be widely disseminated through lab websites, magazines, blogs, and regular media. The research results will be integrated in curricula and programs at UCLA, especially the Ph.D. Major Field of MEMS and nanotechnology. Furthermore, by providing attractive tasks for non-specialists, the project will promote education for undergraduate and high school students. For example, undergraduate students will help develop the field-testing apparatus through many programs at the UCLA engineering school. High school teachers and students can help field-test the SHPo surfaces in their local coastal water, strengthening the outreach programs of UCLA California NanoSystems Institute (CNSI).