ERI: Oscillatory patterns in sessile droplets induced by shear flow of surrounding gas phase

Liquid drops that rest on solid surfaces are called “sessile drops”. This project will study the behavior of sessile drops when air flows past the surface. High-speed imaging shows that in this case sessile drops oscillate before they become dislodged from the surface. The reason for these surprising oscillations is not well understood. The experiments in this project will uncover the causes underlying the drop oscillations. This project will benefit many practical applications, including improving surface washing, reducing ice growth on aircraft, and improving heat transfer operations. This project will benefit society by improving energy efficiency and by training students in advanced experimental techniques. Outreach programs will be conducted to attract high school students to scientific careers. This project will investigate the oscillatory dynamics of sessile droplets exposed to steady shear flow of the surrounding air, focusing on the interplay between drag forces, surface tension, and fluctuating pressure fields. The research addresses two fundamental questions: (1) how does the interaction between drag force and surface tension affect droplet oscillations, and (2) what is the role of the surrounding pressure field in modulating oscillation patterns. High-speed shadowgraphy will be used to capture the dynamics of droplets, while Particle Image Velocimetry (PIV) will be used to reconstruct the surrounding velocity and pressure fields. Experiments will systematically vary surface tension and the velocity of the surrounding air to quantify the competing forces responsible for droplet deformation and oscillation. The analysis will combine force balances with image processing techniques to track droplet motion and scaling laws to interpret the results. By characterizing the inertial effects induced within the droplets, the project aims to provide critical insights into the mechanisms governing contact line depinning. Contact line depinning is the critical step to dislodging the droplet from the surface. The project will generate experimental data and insights to inform future predictive models describing the oscillation frequency and amplitude of the sessile drop. The outcomes will advance the fundamental understanding of droplet dynamics and will benefit applications involving droplets that dislodge from surfaces, such as advanced energy systems, heat exchangers, or anti-fog surfaces. 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.