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

超疏水表面结合了联合收割机的防水性和微尺度纹理，产生了几个令人惊讶的和有用的性能。当浸入水中时，超疏水表面可以在微观空腔内捕获空气层，从而可能减少液体和表面之间的摩擦阻力。减阻超疏水表面可以大大减少能源使用，排放和海上运输成本，以及其他应用。然而，当在实验室或现场在层流和湍流条件下测试时，超疏水表面显示出不一致的性能。最近的工作表明，微量的表面活性剂可以显着削弱层流减阻性能。这一观察结果具有广泛的实际意义，因为表面活性剂天然存在于环境和工程系统中，通常浓度很高。该项目将研究表面活性剂是否也会影响湍流中超疏水表面的性能，解释实验测试中发现的不一致性，以及与现有模型的不匹配，这些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益处的认识。该项目的目标是揭示表面活性剂在现实条件下的影响，以确定实用的减缓策略，并释放超疏水表面在现实应用中的减阻潜力。通过加州大学、圣巴巴拉（美国）和曼彻斯特大学（英国）之间的合作，这将是有史以来第一次通过表面活性剂在湍流中的超疏水减阻的基本建模研究。将实施一种完全解析的数值模拟方法，能够表示超疏水表面上包含表面活性剂的湍流。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，以达到与海洋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。理论模型也将使搜索可能的制度，减阻可以最大化，而数值模拟将提供丰富的详细信息的流动动力学和表面活性剂的效果，并将用于验证理论模型。模拟结果也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知识价值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.