Thin-film flows over topographically patterned surfaces: Free-surface characteristics, atomization, and cleaning

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0854046 StoneThis award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5). Fluid flows over rough surfaces constitute an important and challenging class of problems in fluid dynamics with both industrial applications and natural examples. Many materials and products have a surface texture by design or one that evolves due to natural erosion. The geometric features of the surface texture may be random, with only limited correlations between surface features or made through a machining process with a pattern or structure for decorative reasons, for frictional control, or to improve the adhesive/frictional properties of the surface. The velocity field near a textured surface depends on the texture amplitude and wavelength of the pattern and the thickness of the fluid film. This texture-scale velocity distribution is critical to many processes, such as coating with thin films, surface cooling, cleaning, and drying. The PI will perform systematic experiments and develop theoretical models to explore liquid thin-film flows where the film thickness is comparable to the largest characteristic dimension of the depth of the surface texture. Here three-dimensional effects are significant, and also we focus on phenomena where some aspects of the flow include inertial effects. Flows driven by jet impact on the surface, such as is important in many coating and cleaning processes, will be emphasized. Such flows are important to understand and describe for applications such as atomization in fuel combustion. The study will thoroughly examine new experimental observations, such as the polygonal jump occurring in flow over a rough surface, in contrast to the familiar circular hydraulic jump obtained on a smooth substrate. As another example, polygonal free sheets are precursors to atomization. The PI anticipates uncovering general principles for manipulating thin-film flows using topographic features of a patterned substrate. A systematic experimental study of the physicochemical properties of the fluids and flow parameters, as well as the geometric features of the micro-textured substrates on coating flows, and related sheet flows will be will coupled with modeling and simulations appropriate to the free-surface motions. The PI will continue to involve undergraduates in research, including working with students from underrepresented groups who have participated regularly in the PI's research group the past six years. Several of the research themes will provide demonstration material for the PI's outreach efforts involving public lectures such as the yearly holiday lecture created by the PI for children and their parents (now starting its 8th year), and science demonstrations for local public school students and teachers.