Collaborative Research: A new understanding of droplet breakup: hydrodynamic instability under complex acceleration

液滴的破碎在许多工程应用中都很重要，例如农业喷雾，液体燃料的燃烧以及雨滴对飞机的影响。气体中液滴的破裂是由于气体和液滴速度的差异，作用于液滴表面，就像海洋上的波浪一样。在低速时，液滴在相对恒定的条件下发生破裂。然而，在高速下，液滴的破裂更为复杂，涉及到气体速度的突然变化。在许多高速应用中，例如雨滴对高超音速飞机的冲击，液滴首先会经历气体速度的突然增加，导致快速破裂，随后速度迅速下降，减慢和改变破裂过程。为了设计先进的高超声速飞行器，需要对这些复杂的破碎过程建立准确有效的模型。该项目将采用独特的实验和模拟相结合的方法来研究这些复杂条件下的液滴破裂，并开发一个用于计算机模拟的简单模型。该项目还将让研究生和本科生参与研究和实验设计，训练他们掌握对我们国家安全至关重要的技能。该项目的总体目标是通过建立基于液滴破碎的一般流体动力不稳定性模型，显著提高我们对复杂、可变加速度下液滴破碎的理解。该项目将测试中心假设：液滴破裂是由可变加速度主导的，三层瑞利泰勒不稳定性。模拟将充分解决界面动力学问题，并研究不同加速度历史下不稳定性的增长率。实验将利用高速荧光技术对不同加速历史下的液滴破碎和子液滴大小进行成像。这些测量将用于测试一种新的破碎模型，该模型结合了变加速度流体动力不稳定模型、大尺度液滴变形和动态气滴条件。该破裂模型将在工业过程中的爆炸缓解、高超音速天气影响和先进的基于爆炸的推进循环等广泛应用中发挥预测作用。该模型将使在这些应用中执行系统级模拟成为可能，从而实现液滴事件的准确和高效建模。这项工作的更广泛的影响在于能够有效地模拟对能源效率和国防特别重要的高速多相问题，并吸引不同背景的学生参与多相研究。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The breakup of droplets is important in many engineering applications such as agricultural sprays, combustion of liquid fuels, and the impact of rain droplets on aircraft. The breakup of droplets in a gas occurs due to a difference in the gas and droplet velocities, acting on the droplet surface like waves on the ocean. At low speeds, droplet breakup occurs under relatively constant conditions. However, at high speeds droplet breakup is more complex, involving sudden changes in the gas velocity. In many high-speed applications, such as the impact of rain droplets on hypersonic aircraft, droplets will first experience a sudden increase in gas velocity driving rapid breakup, followed by rapid decrease in velocity, slowing and modifying the breakup process. In order to design advanced hypersonic vehicles, accurate and efficient models for these complex breakup processes are needed. This project will use a unique combination of experiments and simulations to examine droplet breakup under these complex conditions and develop a simple model for use in computer simulations. The project will also engage both graduate and undergraduate students in research and experimental design, training them in skills vital to our national security. The overall goal of this project is to significantly improve our understanding of droplet breakup under complex, variable accelerations by developing a general hydrodynamic instability-based model for droplet breakup. The project will test the central hypothesis: droplet breakup is dominated by a variable acceleration, three-layer Rayleigh Taylor instability. Simulations will fully resolve interfacial dynamics and study the growth rate of instabilities under varying acceleration histories. Experiments will image droplet breakup and child droplet sizes with high-speed fluorescence techniques under different acceleration histories. These measurements will be used to test a new breakup model incorporating variable acceleration hydrodynamic instability models, large-scale droplet deformation, and dynamic gas-droplet conditions. The breakup model will be useful in a predictive capacity in a wide range of applications such as blast mitigation in industrial processes, hypersonic weather impacts, and advanced detonation-based propulsion cycles. The model will make it possible to perform system-level simulations in these applications, enabling accurate and efficient modeling of droplet events. The broader impact of this work lies in enabling efficient simulation of high-speed multiphase problems of particular importance to energy efficiency and national defense and in engaging students of diverse backgrounds in multiphase studies and research.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.