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

利用最近开发的即使在高速流动中也能维持非润湿状态的超疏水(SHPO)表面，加州大学洛杉矶分校的团队建议阐明它们如何在湍流中经历如此减少的阻力(减少50%)。湍流边界层流中的减阻特性将在很大范围的雷诺数范围内进行实验和数值表征，这些雷诺数代表运动中的水上交通工具。所开发的SHPO表面的最终用途将被海洋环境中的现场测试所证实。智能优点：尽管在过去的十年中对SHPO表面进行了大量的研究，但在获得可展开用于实际应用的SHPO表面方面仍然存在挑战。虽然减阻是SHPO表面预期的最吸引人的特征，但没有一个表面在野外条件下表现出减阻效果，例如在室外水域中。虽然减阻要求SHPO表面处于去湿状态作为必要条件，但去湿状态在水下是非常脆弱的。无论做什么，被困住的气体最终都会扩散到周围的水中，最终使表面湿润。最近，PI的实验室开发了一种半活动SHPO表面，即使在几十米深的情况下也能保持数月的去湿状态，从而极大地提高了水下SHPO表面的耐用性。此外，在湍流边界层流中的一些被动SHPO表面上，他们还获得了50%以上的减阻效果。这些表面也被发现即使在高速流动中也不润湿。在这些最新突破的推动下，加州大学洛杉矶分校的团队建议找到湍流中SHPO表面大幅减阻的基本物理，并在大范围的雷诺数(5x10E5-2x10E7)上建立减阻。最终，他们将使用一艘小船在现场条件下展示减阻效果。布罗德影响：减少流动液体的摩擦阻力长期以来一直是流体工程学中一个难以实现的目标。如果减阻是可持续的实际条件，仅节能一项就会带来显著的经济和环境效益。他提出的研究旨在解释流动中某些SHPO表面上的阻力是如何减少的，这些流动代表了大多数水上交通工具的一般行驶条件。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，特别是微机械和纳米技术的博士专业领域。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帮助在当地沿海水域实地测试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).