Understanding the role and use of superhydrophobic coatings for aircraft and powerplant icing

本项目是为期一年的“飞机防冰超疏水涂层的疏冰评价”项目的延续。设计的超疏水涂层（SHC）小型翼型在防冰和除冰两种模式下都表现出良好的性能。结果表明，在完全蒸发的情况下，使用SHC翼型可节省高达75%的热量输入。该项目旨在通过数值和实验相结合的研究，将技术准备水平（TRL）从2提高到4。由于缺乏对液滴/表面相互作用的基本理解，特别是在空气剪切流存在的情况下，很难实现适当的涂层开发。本文提出的实验/数值研究不同于以往的研究，因为它不仅从涂层的应用、制造和结冰特性的角度出发，而且从表面水滴动力学的角度出发，对涂层问题进行了全面的研究。它将特别关注在静态和动态（冲击）条件下滴与超疏水表面的相互作用。还将调查目前使用的未经处理的铝表面，以建立基线。最初的研究将集中在使用由各种超疏水表面制成的扁平片状固定液滴的滑动行为上。本研究将扩展到液滴撞击平面后的滑动行为研究（即液滴撞击不同疏水性表面的动力学）。除了实验程序之外，还将开发液滴撞击表面的数值模型，该模型将使用从实验研究中产生的静态和动态接触角信息来检查表面处理。我们将使用流体体积（VOF）方法来模拟液气界面的变形以及凝固和相变。从这些模型研究学到的原则将被应用到一个翼型的情况下，试图产生超疏水涂层的应用机翼和机舱的建议。此外，SHC的磨损和侵蚀机制将被广泛研究，以提高其在紫外线和污垢暴露方面的寿命。

This project is the continuation of a one-year project on "Ice-phobic evaluation of superhydrophobic coatings for aircraft icing protection". The devised superhydrophobic coated (SHC) small scale airfoil showed promising performance in both anti- and de-icing modes. It was demonstrated that for fully evaporative case, using SHC airfoil provides up to 75% savings on heat input. This proposed project is aimed at improving the technology readiness level (TRL) from 2 to 4 through a combined numerical and experimental study. The absence of fundamental understanding of the drop/surface interactions, especially in the presence of an air shear flow, has made it difficult to achieve proper coating development. The proposed experimental/numerical study is different from past investigations in that it takes a comprehensive approach to the issues of coatings, not only from the point of view of application, fabrication and icing characteristics, but also that of water drop dynamics on surfaces. It will specifically focus on drop interactions with superhydrophobic surfaces in static and dynamic (impact) conditions. Untreated aluminum surface currently in use will also be investigated to establish a baseline. Initially the study will focus on sliding behavior of stationary drops using flat coupons made of various superhydrophobic surfaces. This study will be extended to study the sliding behavior of a drop after its impact on the flat surface (i.e. the dynamics of drop impact on surfaces with various hydrophobicities). Alongside the experimental program, a numerical model of a drop impacting on a surface will also be developed which will use the static and dynamic contact angle information generated from experimental studies to examine surface treatments. We will use the proven method of Volume of Fluid (VOF) in order to model the deformation of liquid-gas interface as well as the solidification and phase change. Learned principles from these model studies will be applied to case of an airfoil in an attempt to generate recommendations for application of superhydrophobic coating for wings and nacelles. In addition, wear and erosion mechanisms for SHC will be extensively studied to improve its longevity in terms of UV and dirt exposure.