Solid-liquid Interactions and Interfacial Water Structuring Determine Slip and Drag in Turbulent Boundary Layer Flows

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Fluid friction and drag are ever-present phenomena, and particularly important issues in transportation systems. Fluid drag is an energy consumption barrier that must be continuously overcome by carriers transporting people and goods across the globe; thus, reducing fluid drag translates not only into more effective and viable transportation systems, but also in more ecofriendly ships. Increasing fluid slip at solid surfaces in contact with water is a potential drag-reduction mechanism. Surface engineering can be used to generate slip-surfaces; however, the fundamental mechanisms of slip in turbulent flows are not well understood. Therefore, the main objective of this project is to conduct a fundamental investigation into the mechanisms of hydrodynamic slip using a combination of sophisticated modeling techniques and experiments. This project will also create a general-public-oriented podcast where the investigators will present their findings to the public in a candid and accessible manner. Graduate and undergraduate students will be involved in the research and outreach activities of the project, where the promotion of equity and inclusion of underrepresented populations will be set as a mission.The goal of this project is to bridge the knowledge gap between experimental observations and numerical/theoretical calculations of hydrodynamic slip in high-shear rate flows. Similarly, through the combination of surface characterization techniques and numerical simulations at different length scales, the conceptual mismatch between the microscopic mechanisms of slip and macroscopic drag calculations will be addressed. To achieve these goals: (i) molecular dynamics simulations and theory will be used to create physics-informed models of solid-water interfaces able to calculate hydrodynamic slip and interfacial water structuring; (ii) sum frequency generation vibrational spectroscopy and atomic force microscopy will be used to validate not only the slip calculations, but also to verify the interfacial liquid property relation to slip calculations; and (iii) direct numerical simulations and wall modeled large eddy simulations will be used for the first time to model drag using physics-informed boundary conditions to further contribute to the design of engineered surfaces with low drag. The research output from this project will advance the fields of fluid dynamics and surface science, particularly in areas where drag reduction is paramount for the reduction of energy consumption.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.