Effects of hydrophobicity-induced wall slip on turbulence drag and turbulence structure

该奖项是根据2009年美国复苏和再投资法案（公法111-5）资助的。CBET-0853657 Papavassiliou，Dimitrios V.该项目将研究可能导致固-液界面处流体滑移的基本分子机制，以及流体滑移如何确切地影响远离粘性壁亚层的湍流结构。最近已经证明，超疏水表面诱导在其上移动的流体中的滑动。对于层流，在壁面处的这种滑移导致了实验和计算都观察到的阻力减小。最近的计算工作表明，超疏水表面可以导致湍流减阻，只有当它们导致显着的流体在壁面滑移。 湍流减阻已经通过引入非常少量的添加剂（例如聚合物、表面活性剂或微泡）来实现。这种方法主要适用于内部流动。然而，当流体在物体周围流动时，使用添加剂来改变流体性质充其量是不切实际的。如果处理管道（或车辆）表面，使其变得超疏水可以导致减阻，那么这种处理将提供一种对内部和外部流动都可行的减阻技术。 本研究的重点是在固体-水界面处产生流体滑移的条件的基本调查，以及这种滑移可能对湍流减阻的影响。具体的问题进行调查，包括疏水性和流体滑移之间的相关性及其解释的基础上的分子结构的流体旁边的固体-流体界面，流体的类型和类型的接口，可以导致流体滑移的探索，并确定的机制，其中滑影响湍流的产生和维持。 这些发现对于固体表面附近的流体流动和湍流理论以及许多工业应用都具有重要意义。该研究项目的各个方面将有助于开发新课程，并将纳入现有课程。此外，通过该项目产生的数据库将通过现有的网络服务器提供给社区，并计划建立可作为验证基准的数据库。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5). CBET -0853657 Papavassiliou, Dimitrios V.This project will investigate the fundamental molecular mechanisms that can result in fluid slip at a solid-fluid interface and how exactly, if at all, fluid slip affects the structure of turbulence away from the viscous wall sublayer. It has been recently documented that ultra-hydrophobic surfaces induce slip in fluids moving over them. For laminar flows, this slip at the wall results in drag reduction that has been observed both experimentally and computationally. Recent computational work shows that ultra-hydrophobic surfaces can lead to turbulent drag reduction only when they result in significant fluid slip at the wall. Turbulent drag reduction has been achieved with the introduction of a very small amount of additives, such as polymers, surfactants or microbubbles. Such methods are mainly feasible for internal flows. However, when a fluid flows around an object, the use of additives to alter the fluid properties is at best impractical. If treating a conduit (or a vehicle) surface such that it becomes ultra-hydrophobic can result in drag reduction, then such treatment will present a drag-reduction technology feasible for both internal and external flows. This study is focused on the fundamental investigation of the conditions that generate fluid slip at the solid-water interface, and the effects that such slip can have on turbulence drag reduction. Specific issues to be investigated include the correlation between hydrophobicity and fluid slip and its interpretation based on the molecular structure of the fluid next to a solid-fluid interface, the exploration of the type of fluid and the type of interface that can result in fluid slip, and the determination of the mechanism by which slip affects the generation and maintenance of turbulence. These findings will be significant for the theory of fluid flow next to solid surfaces and for turbulence, as well as for many industrial applications. Aspects of this research project will be instrumental in the development of a new course and will be integrated in existing courses. In addition, the database generated through this project will become available to the community through existing web servers, and databases that can serve as validation benchmarks are planned.