Lamella Edge Dynamics

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Zhang, Wendy 1336489Recent experiments as well as developing technologies are motivating a re-assessment of our theoretical framework for understanding drop impact and splash. The proposed theoretical/ numerical study on the dynamics at the leading edge of a fluid lamella ejected by impact will fulfill this aim. It will assess the potential for adapting the known phase diagram for Newtonian liquid impacts to dense suspension plug impacts, a phenomenon important in thermal spray coating and inkjet printing of metallic and ceramic machine parts. It will also investigate the stability of lamella edge dynamics. Recent experiments show small effects such as a reduction in ambient pressure and/or surface roughness can stabilize lamella edge and prevent splash, even in impact regimes where splash was previously thought to be inevitable. This study will develop a asymptotic model for air vorticity induced by lamella flow, incorporate associated air stresses into a lubrication flow model for the liquid lamella and compare their results against two-phase flow simulations and experiments.Intellectual Merit :The proposed study will advance the current state of scientific understanding by bridging an existing gap between the existing theoretical framework for liquid impact and recent experimental findings. Our current framework asserts that the outcome of liquid drop impact is dictated by the impact speed, the substrate roughness, the substrate slip condition, and the material properties of the impacting drop. Properties of the ambient airflow are held to be unimportant and surface roughness is thought to lead to more splashing. In contrast, experiments clearly show more subtle outcomes. Success in bridging this gap between theory and experiment will transform our understanding. Finally a physically motivated, accurate model for the leading edge motion provides a theoretical tool for understanding the structures formed by the impact of more complex fluids such as liquid metals and suspensions. Broader Impacts :The work proposed herein would enhance the efficiency of spray coating, which is important for the sharpness of images created by inkjet printing, and the fine-scale resolution of objects manufactured by 3D printing. These processes improve significantly if splash can be eliminated. In contrast, the efficiency of a diesel engine depends crucially on completely fragmenting the injected streams of liquid fuel into small droplets. Maximizing the amount of splash, improves efficiency and reduces exhaust. While the gas pressure inside an engine chamber cannot be easily varied, an understanding of how a larger ambient gas pressure induces splash formation opens the possibility that one can engineer other aspects of the technology, e.g. surface roughness, to mimic this high pressure behavior.The proposed research also provides an excellent education for both the graduate student and thepostdoctoral scholar. Undergraduate students will work on this project as part of the University ofChicago's Research Experience for Undergraduates (REU) program. The University of Chicago REU program focuses on providing students from under-represented minority groups opportunities to work in research. Previous under-represented minority students mentored it he PI's lab have gone on to pursue graduate education in Chemical Engineering and Physics. In a broader context, research results will also be incorporated into the curriculum of two elective courses (one undergraduate / one graduate), and developed into a demonstration for the annual science open house at the PI's department.