UNS: Robust Superhydrophobic Surfaces for Enhanced Propulsive Performance and Maneuverability at Intermediate Reynolds Number

#1510707Krueger，Paul S.这项提议的目标是通过使用超疏水表面来改善推进力。当水滴在表面上形成珠状，并且水滴与表面之间的角度大于150度时，表面被定义为超疏水。在这样的情况下，可以实现减阻，因为水在超疏水表面上滑动，并且可以在推进中实现节能。在超疏水表面引入表观滑移，利用表面微结构捕获表面附近的气体，可以导致减阻。然而，众所周知，这样的表面有其自身的挑战，包括在增加的静压或动压下气膜崩溃，气膜因扩散而逐渐耗尽，以及滑移长度受到微结构特征间距的限制。这项拟议的工作旨在通过对气膜加压来扩大超疏水表面的适用性，这将允许气膜在压力扰动和扩散时保持强大的稳定性。气动稳定还有一个额外的优点，即改变气膜压力将允许微结构特征间隔更远，增加表观滑移率，并且压力的动态变化将允许直接控制表面行为，包括气膜的重新初始化。气动控制表面将由聚二甲基硅氧烷使用激光微加工和软光刻技术构建，并在中等雷诺数(Re)流动下测试扑翼和脉冲喷射推进方法。研究了超疏水表面引入的表观滑移对扑翼和脉冲喷气推进流场推进性能的影响。还将研究动态驱动气膜的能力。第二个结果将是提高开发和维持超疏水表面的技术能力，扩大它们的应用领域，使其适用于其他减阻和自清洁表面。提出了通过暑期沉浸进行本科生教育的活动，并将编写关于机械和生物推进的网络教程，供学生和社区使用。

#1510707Krueger, Paul S.The goal of this proposal is to improve propulsion by using superhydrophobic surfaces. A surface is defined as superhydrophobic when water droplets bead on the surface, and the angle between the drop and the surface is larger than 150 degrees. In cases like this, one can achieve drag reduction, since water slips on the superhydrophobic surface, and energy savings can be realized in propulsion. The introduction of apparent slip at the superhydrophobic surface using gas trapped near the surface by the microtexture of the surface can lead to drag reduction. However, it is known that such surfaces have their own challenges, including collapse of the gas film under increased hydrostatic or dynamic pressure, gradual depletion of the gas film by diffusion, and slip lengths limited by the spacing of the microtexture features. The proposed effort seeks to expand the applicability of superhydrophobic surfaces by pressurizing the gas film, which will allow for robust stabilization of the gas film against pressure disturbances and diffusion. Pneumatic stabilization has the additional advantages that changing the gas film pressure will allow mictotextured features to be spaced further apart, increasing the apparent slip, and dynamic variation of the pressure will allow for direct control of the surface behavior, including re-initialization of the gas film. Pneumatically controlled surfaces will be constructed from polydimethylsiloxane using laser micromachining and soft lithography techniques and tested on flapping-fin and pulsed-jet propulsion methods at intermediate Reynolds number (Re) flows. The effect of apparent slip introduced by the superhydrophobic surfaces on the propulsive performance of flow fields generated by flapping-fin and pulsed-jet propulsion will be investigated as a function of Re. The ability to dynamically actuate the gas film will also be investigated. A secondary outcome would be an improved technical capability in developing and sustaining superhydrophobic surfaces broadening the areas of their application to other cases of drag reduction and self-cleaning surfaces. Activities on undergraduate education through summer immersion were proposed and a web-based tutorial on mechanical and biological propulsion will be developed and made available to students and the community.