博士论文答辩：表面性质对液滴撞击行为的影响：单滴与双滴动力学研究
日期：2025/05/23 - 2025/05/23
博士论文答辩：表面性质对液滴撞击行为的影响：单滴与双滴动力学研究
主讲人：Nuri Erdem Ersoy, Ph.D. candidate at UM-SJTU Joint Institute
时间：2025年5月23日（周五）上午10:00
地点：密西根学院龙宾楼503会议室
讲座摘要
Droplet impact on various surfaces and geometries has applications in both traditional and emerging fields, such as microelectronics, biomedical engineering and internal combustion engines. While extensive research has been conducted on homogeneous surfaces and geometries, the influence of more complex surface characteristics on single and double droplet impacts remains underexplored. This is particularly true for surfaces with multiple surface roughness characteristics and geometries comparable in size to the droplets. Understanding this phenomenon requires a thorough investigation of surface properties including hydrophobic and hydrophilic characteristics, flat and convex geometries, smooth and rough textures, and dual roughness surfaces. This dissertation investigates the effects of these surface properties on single and double droplet impact dynamics, with a particular focus on expansion behavior and asymmetric rim formation on dual roughness surfaces.
Using high-speed imaging and image analysis methods, experiments were conducted to investigate droplet impact on single- and dual-roughness surfaces. For single droplet impacts, findings revealed an additional dissipation mechanism at the interface of dual roughness surfaces, as evidenced by a reduction of up to 12% in longitudinal spreading. To quantify this additional dissipation, an energy-based model was introduced. The model demonstrated strong agreement with experimental data, accurately capturing the observed reduction in longitudinal spreading. Additionally, a transition zone that significantly influences the formation of secondary droplets and a novel “interface finger” mechanism was identified. Different from single droplet impacts, double droplet impact scenarios produced distinct central rising sheet morphologies. Moreover, analysis using Bond number and circularity indicated that gravity has no influence on the early phase of the central rising sheet's evolution. Depending on the impact conditions, three different forms of the central rising sheet were identified: a semilunar type, a curved-base type, and an irregular type without clear sheet formation. Furthermore, on dual roughness surfaces, increasing the step change in surface roughness resulted in less stable and more asymmetric central rising sheets. To determine the maximum height and the thickness of the sheet at the time of maximum expansion, a theoretical analysis based on the volume and expansion characteristics was conducted and demonstrated as a useful method.
This dissertation significantly enhances the understanding of droplet dynamics by developing novel frameworks for analyzing single and double droplet impacts on surfaces with varying roughness, discovering previously unidentified phenomena such as "interface finger" formation, and delivering predictive models for energy dissipation influenced by step change in surface roughness. These contributions provide valuable insights and tools for a wide range of applications, including inkjet printing, spray coating, and microfluidics, where precise control over droplet impact behavior on rough surfaces is essential.
主讲人介绍
Nuri Erdem Ersoy, originally from Turkey, earned his bachelor's degree from Middle East Technical University and his master's degree from the University of Michigan–Shanghai Jiao Tong University Joint Institute. During his post graduate studies, he specialized in droplet impact dynamics, investigating capillary waves, mixing, target surface effects, interface evolution, and surface roughness. He has published five papers in top-tier journals, four as first author. Currently, his PhD research focuses on single and double droplet impacts on dual-roughness surface interfaces.