Lamella Edge Dynamics

1336489最近的实验和发展中的技术促使我们重新评估我们理解跌落冲击和飞溅的理论框架。本文提出的对受冲击喷射的流体薄片前缘动力学的理论/数值研究将实现这一目标。它将评估将牛顿液体碰撞的已知相图应用于密集悬浮塞碰撞的潜力，这是金属和陶瓷机器部件的热喷涂涂层和喷墨打印中重要的现象。它还将研究片层边缘动力学的稳定性。最近的实验表明，降低环境压力和/或表面粗糙度等微小影响可以稳定薄片边缘并防止飞溅，即使在以前认为不可避免的飞溅的冲击状态下也是如此。本研究将建立由片层流动引起的空气涡度渐近模型，将相关的空气应力纳入液体片层的润滑流动模型，并将其结果与两相流模拟和实验结果进行比较。智力优势：拟议的研究将通过弥合现有的液体撞击理论框架与最近的实验发现之间的差距，推进目前的科学理解状态。我们目前的框架断言，液滴撞击的结果是由撞击速度、基材粗糙度、基材滑移条件和撞击液滴的材料特性决定的。周围气流的特性被认为是不重要的，表面粗糙度被认为会导致更多的飞溅。相比之下，实验清楚地显示出更微妙的结果。成功地弥合理论与实验之间的差距将改变我们的理解。最后，前缘运动的物理动机，精确的模型为理解更复杂的流体（如液态金属和悬浮液）的影响所形成的结构提供了理论工具。更广泛的影响：本文提出的工作将提高喷涂的效率，这对于喷墨打印产生的图像的清晰度和3D打印制造的物体的精细分辨率至关重要。如果能够消除飞溅，这些过程将得到显著改善。相比之下，柴油发动机的效率主要取决于将注入的液体燃料流完全分解成小液滴。最大限度地提高飞溅量，提高效率并减少废气。虽然发动机舱内的气体压力不能轻易改变，但了解更大的环境气体压力如何引起飞溅形成，为设计技术的其他方面（例如表面粗糙度）提供了可能性，以模拟这种高压行为。建议的研究也为研究生和博士后学者提供了良好的教育。作为芝加哥大学本科生研究经验（REU）计划的一部分，本科生将参与该项目。芝加哥大学REU项目的重点是为代表性不足的少数群体的学生提供从事研究工作的机会。以前在PI实验室指导过的少数族裔学生已经继续攻读化学工程和物理学的研究生教育。在更广泛的背景下，研究成果也将纳入两门选修课程（一门本科生/一门研究生）的课程，并发展成为PI部门年度科学开放日的演示。

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.