ERI: Evolution of Detached Liquid Sheet Edges from Patterned Boundaries

The complex ways in which sheets of liquid break up at their edges to form droplets are important to the understanding of spray characteristics, for example the eventual size of the droplets produced. As sprays are encountered in numerous natural and engineered scenarios involving liquids, their study is important both at a fundamental and applied level. The aim of this project is to develop an experimental platform to explore the role of micropatterned boundaries on the evolution and subsequent breakup of liquid sheet edges. Project results can be used to validate numerical and computational studies of breakup mechanisms. The project, part of the Engineering Research Initiation program, will take place at a primarily undergraduate serving institution of higher education and will give student groups from existing project-based courses the opportunity to develop experimental equipment. Additional student participants will benefit from existing campus programs - one of which is directly tied to university efforts at improving and promoting diversity, equity, and inclusivity in STEM – providing excellent mentoring and professional development opportunities. The goal of this project is to improve experiments to explore the breakup of liquid sheet edges, fundamental to the formation of droplets by sprays, by investigating the influence of micro-scale patterns on the physical boundaries from which the edges are created once liquid sheets are detached. Previous experiments have used rapid heating of metal wire frames to form the edges of liquid films (soap films). The key questions this project proposes to answer are: (1) Instead of using an unadulterated metallic wire to form the initial edge of a liquid sheet for detachment experiments that use rapid boiling to free the edge, can an edge, or boundary, be created with micro-scale patterns to induce disturbances of a known spatial wavelength onto that liquid film edge? (2) If this is possible, what is the nature of the influence of the modulated disturbance on the evolution of the edge? (3) Is it then possible to demonstrate measurements of modulated instability growth to determine, without ambiguity, fastest growing wavelengths to further understand the evolution and breakup, via instability, of the detached liquid sheet edge? To answer these questions, challenging experiments using high-speed photography and at high spatial resolution will be performed. By developing these experimental techniques to answer the key questions, the project will provide useful avenues for future study of liquid sheet breakup. 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.