Capillary-gravity wave scattering from barriers with pinned contact lines

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Capillary-gravity waves are waves traveling along free surfaces of liquids and are often confined in a narrow channel. The proposed research is designed with the goal of achieving an improved understanding of the fundamental fluid physics underlying surface wave interactions with a rigid wall. The three-phase liquid-air-solid boundary influences the liquid behavior, which is important in laboratory studies and also in industrial applications, for instance, the dynamics of drops attached to a solid wall, liquid oscillations in closed basins, liquid globes and lenses attached to thin wire loops, liquid cylinders stabilized by helical wires, and wave propagation and flows in open narrow channels. The understanding provided by this research will enable the development of new designs and models that will lead to more efficient liquid management involving minimal solid contact. The results will be applicable to engineering areas including condensation heat transfer, liquid-gas contacting processes, and chemical engineering applications, as well as applications in biology and biotechnology. The approaches developed from this project will also provide new methods for measuring and modeling fluid behavior involving three-phase boundaries. The project will also contribute to the preparation and diversification of the STEM workforce involving undergraduates, graduate students, and a mid-career stage faculty member. The proposed research will use laboratory and computational experiments to improve the understanding of the fundamental fluid physics underlying the scattering of travelling capillary-gravity waves from a surface-intersecting rigid barrier, where contact lines pin the free surface of the liquid at a barrier's edge. The laboratory experiments will use an acoustic method of airborne ultrasound reflected out the water surface to measure the amplitude of capillary-gravity waves. The computational experiments will concern inviscid linear waves in incompressible and irrotational flow by finite-element simulations using commercially available software. Specifically, the project will study (i) contact line effects in the transition from gravity wave scattering to capillary wave scattering, (ii) the dependence of wave scattering on the barrier's geometric parameters, and (iii) the effect of menisci near the barrier walls where the liquid surface is curved. Understanding how contact lines at three-phase boundaries influence the dynamics of a free liquid surface is essential in surface-tension dominated fluid dynamics. Prior studies involving contact line effects on capillary dynamics focused mainly on the frequency dependence and the damping of standing-wave modes. In contrast, the proposed research will fill the gap of knowledge in capillary-gravity wave scattering from rigid structures with contact line effects. Since the 1960s theoretical studies have attempted to predict the contact line effects on capillary-gravity wave scattering, but progress has been hindered by the limitation of ideal assumptions made in the models, and by the lack of experimental data for the understanding of the fluid physics. The proposed laboratory experiments will provide the first quantitative results on the effect of contact lines on the scattering. The laboratory and computational experiments should systematically improve the knowledge on the fluid physics of the scattering and yield new insights on the influence of contact lines and menisci, and on the dependence on wave and structure parameters.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.