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是重要的，例如农业喷雾、液体燃料的燃烧以及雨滴对飞机的影响。由于气体和液滴速度的差异，气体中液滴的分裂发生，就像海洋上的波浪一样作用在液滴表面上。在低速下，液滴破碎在相对恒定的条件下发生。然而，在高速下，液滴破碎更复杂，涉及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，液滴将首先经历气体速度的突然增加，从而驱动快速破碎，然后速度迅速降低，从而减缓和修改破碎过程。为了设计先进的高超声速飞行器，这些复杂的破碎过程的准确和有效的模型是必要的。该项目将使用实验和模拟的独特组合来研究这些复杂条件下的液滴破碎，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，培训他们对我们的国家安全至关重要的技能。这个项目的总体目标是显着提高我们的理解液滴破碎复杂的，可变的加速度下，通过开发一个通用的流体动力学不稳定性为基础的模型液滴破碎。该项目将测试中心假设：液滴破碎是由一个可变的加速度，三层瑞利泰勒不稳定性。模拟将完全解决界面动力学和研究增长率的不稳定性在不同的加速度的历史。实验将图像液滴破碎和子液滴的大小与高速荧光技术在不同的加速度历史。这些测量将被用来测试一个新的崩溃模型，将可变加速度流体动力学不稳定模型，大规模的液滴变形，和动态的气体液滴条件。破裂模型将在广泛的应用中具有预测能力，例如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。该模型将使在这些应用中执行系统级仿真成为可能，从而实现对液滴事件的准确和有效建模。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和研究。该奖项反映了NSF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.