CBET-EPSRC: Surfactant impact on drag reduction of superhydrophobic surfaces in turbulent flows

超疏水表面结合了憎水性和微尺度纹理，产生了一些令人惊讶和有用的特性。当浸入水中时，超疏水表面可以将空气层困在微小的空腔中，潜在地减少液体和表面之间的摩擦阻力。减阻超疏水表面可以极大地减少海上运输以及其他应用中的能源消耗、排放和成本。然而，在实验室或现场进行层流和湍流条件下的测试时，超疏水表面表现出不一致的性能。最近的工作表明，微量的表面活性剂会显著影响层流中的减阻性能。这一观察结果具有广泛的实际意义，因为表面活性剂自然存在于环境和工程系统中，通常浓度很高。这个项目将调查表面活性剂是否也会影响湍流中超疏水表面的性能，解释在实验测试中发现的不一致，以及与现有模型的不匹配，现有模型目前都忽略了表面活性剂。该项目还将通过与当地社区的外联计划，提高公众对减阻技术及其好处的认识。该项目的目标是揭示表面活性剂在现实条件下的影响，以便确定实用的缓解策略，并释放超疏水表面在现实世界应用中的减阻潜力。这将通过加州大学圣巴巴拉分校(美国)和曼彻斯特大学(英国)合作进行的关于表面活性剂在湍流中超疏水减阻的首次基本模拟研究来进行。将实施一种全分辨率的数值模拟方法，能够表示超疏水表面上包含表面活性剂的湍流流动。该模拟方法将使用先进的网格细化技术，并将在并行超级计算机上运行，以获得与海上应用的现实条件相关的流态。此外，将开发更简单的理论模型来识别和预测关键现象。理论模型还可以寻找减阻最大化的可能区域，而数值模拟将提供大量关于流动动力学和表面活性剂效果的详细信息，并将用于验证理论模型。模拟结果还将在线提供给其他寻求在表面活性剂存在下提高超疏水表面性能的研究人员。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Superhydrophobic surfaces combine water repellency and microscale texture to yield several surprising and useful properties. When immersed in water, superhydrophobic surfaces can entrap an air layer inside microscopic cavities, potentially reducing friction drag between the liquid and the surface. Drag-reducing superhydrophobic surfaces could greatly reduce energy use, emissions, and cost for maritime transport, as well as in other applications. However, superhydrophobic surfaces have shown inconsistent performance when tested in the laboratory or in the field in both laminar and turbulent flow conditions. Recent work has revealed that trace amounts of surfactants can significantly impair the drag-reduction performance in laminar flows. This observation has vast practical implications, since surfactants are naturally present in the environment and in engineering systems, often at large concentrations. This project will investigate whether surfactant can also affect the performance of superhydrophobic surfaces in turbulent flows, explaining inconsistencies found in experimental tests, as well as the mismatch with existing models, which currently all ignore surfactant. The project will also develop public awareness about drag-reduction technology and its benefits through outreach programs with local communities.The goal of this project is to uncover the impact of surfactant in realistic conditions, in order to identify practical mitigation strategies and unlock the drag-reduction potential of superhydrophobic surfaces for real-world applications. This will be pursued through the first-ever fundamental modelling investigation of superhydrophobic drag reduction in turbulent flow with surfactant, through a collaboration between the University of California, Santa Barbara (US) and the University of Manchester (UK). A fully-resolved numerical simulation approach will be implemented, capable of representing surfactant-inclusive turbulent flow over superhydrophobic surfaces. The simulation approach will use advanced mesh refinement techniques, and will run on parallel supercomputers in order to reach flow regimes relevant to realistic conditions for maritime applications. In addition, simpler theoretical models will be developed to identify and predict key phenomena. The theoretical models will also enable searching for likely regimes where drag reduction can be maximized, whereas the numerical simulations will provide a wealth of detailed information about the flow dynamics and the effect of surfactants, and will be used to validate the theoretical models. The simulation results will also be made available online to other researchers seeking to advance the performance of superhydrophobic surfaces in the presence of surfactants.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.