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

利用最近开发的超疏水（SHPo）表面，即使在高速流动中也能保持非润湿状态，加州大学洛杉矶分校的团队建议阐明它们是如何在湍流中经历如此减少的阻力（减少50%）的。在紊流边界层中，阻力减少将在很大的雷诺数范围内进行实验和数值表征，紊流边界层代表了运动中的水载体。开发的SHPo表面的最终效用将通过海洋环境的现场试验来证实。知识优势：尽管在过去十年中对SHPo表面进行了大量研究，但在获得可部署于实际应用的SHPo表面方面仍然存在挑战。虽然减阻是SHPo表面最具吸引力的特性，但目前还没有一种表面在现场条件下（如室外水域）显示出减阻效果。而减阻要求SHPo表面处于脱湿状态是必要条件，但脱湿状态在水下是非常脆弱的。无论你做什么，被困住的气体最终都会扩散到周围的水中，最终使表面变湿。最近，PI的实验室通过开发一种半活性SHPo表面，大大提高了水下SHPo表面的坚固性，这种表面即使在几十米深的水下也能保持数月的脱水状态。此外，在湍流边界层流动中，他们在一些被动SHPo表面上获得了50%以上的减阻效果。这些表面即使在高速流动中也不湿润。在这些最新突破的推动下，加州大学洛杉矶分校的研究小组提出，要找到湍流中SHPo表面大幅减阻的潜在物理原理，并在广泛的雷诺数范围内（5x10E5 - 2x10E7）建立减阻。最终，他们将利用一艘小船在野外条件下演示减阻效果。更广泛的影响：减少流动液体的摩擦阻力一直是流体工程中难以实现的目标。如果减阻是可持续的实际条件下，仅节能就会给经济和环境带来显著的效益。他提出的研究旨在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。研究成果将纳入加州大学洛杉矶分校的课程和项目，特别是MEMS和纳米技术的博士专业。此外，通过为非专业人员提供有吸引力的任务，该项目将促进大学生和高中生的教育。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他们当地的沿海水域实地测试SHPo表面，从而加强加州大学洛杉矶分校加州纳米系统研究所（CNSI）的推广项目。

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).