CAREER: Transition, Turbulence and Mixing in Shock-Accelerated Variable Density Flows at Extreme Conditions

许多关于混合的研究集中在不可压缩介质中的不稳定性和湍流所起的作用。然而，压缩性和冲击在许多实际应用中起着至关重要的作用。例如，了解火山喷发中羽流的行为，设计用于惯性约束聚变的更有效的燃料颗粒，利用冲击波粉碎胆结石或肾结石，以及开发节能的超燃冲压发动机。理解这种复杂流动中的混合过程，提出了流体力学中一系列真正基本和开放的问题，这些问题仍有待解决。这个CAREER项目正是在这个背景下提升了我们的知识，然后可以应用到这些实际应用中。CAREER项目的科学目标是在可压缩系统中产生、诊断和模拟激波驱动的湍流。该系统将流体动力学不稳定性与辐射和等离子体的影响解耦。该方法是使用一个新建的可变倾斜激波管，其内横截面为11.5cm × 11.5cm，配备了最先进的激光诊断（3D粒子图像测速，平面激光诱导荧光以及瑞利散射），以回答与激波驱动的变密度流相关的关键科学问题，这些问题尚未被探索。智力优势：本研究将量化初始条件（单模和多模）、入射激波马赫数(M)和密度对比对扰动增长和混合速率的影响，并确定自相似标度定律的存在，以及在这些极端混合环境中发生过渡所需的雷诺数和长度标度临界值。作为该项目的一部分进行的实验将提供第一个详细的湍流统计测量（即，雷诺应力，密度-速度相关性及其光谱），用于m2.0的冲击加速变密度流，并将通过在更现实的条件下进行测试，为模拟中使用的基于物理的模型提供信息。这项研究将有助于发展准确预测和模拟极端混合的能力，可能导致许多领域的进步：能源、环境（大气和海洋学）、航空航天工程、化学加工、国土安全，以及最相关的惯性约束聚变（ICF）装置。更广泛的影响：综合教育计划将让第一代大学生参与实验设计和操作，支持一名女研究生参与拟议的研究，并使用可视化和基于团队的方法来提高学生对概念的理解，促进对成功至关重要的沟通和团队合作技能。第一代学生参与研究将提高这些学生在系里的保留率和成功率。一个基于小程序的视觉学习环境可以让学生观察动态现象，探索不同参数对结果解的影响，从而增强课堂上材料的学习和记忆。为了提高公众对激波驱动流及其潜在应用的认识，我们计划与当地一位高中教师合作，制作有关我们的研究和实验设施的信息视频，并将其发布在YouTube上，供教师在课堂上使用。

1254760RanjanMany studies of mixing focus on the role played by instabilities and turbulence in an incompressible medium. However, compressibility and shocks play a critical role in many practical applications. Some examples are understanding the behavior of plumes in volcanic eruptions, design of more efficient fuel pellets for inertial confinement fusion, fragmentation of gallstones or kidney stones by shock waves, and development of energy-efficient scramjet engines. Understanding the mixing process in such complex flows presents a set of truly fundamental and open problems of in fluid mechanics that still remain to be solved. This CAREER project advances our knowledge precisely in this context, which can then be applied to these practical applications. The scientific goal of the CAREER project is to produce, diagnose, and simulate shock-driven turbulent flows in a compressible system. The system decouples hydrodynamic instabilities from the effects of radiation and plasma. The approach is to use a newly built variable-inclination shock tube with 11.5cm × 11.5cm square inner cross-section, equipped with the state-of-the-art laser diagnostics (3D Particle Image Velocimetry, Planar Laser-Induced Fluorescence, as well as Rayleigh-Scattering), to answer critical scientific questions associated with shock-driven variable-density flows in configurations and regimes which have not yet been explored.Intellectual Merit: This research will quantify the effects of initial conditions (single and multimode), incident shock wave Mach numbers (M), and density contrast on the perturbation growth and mixing rate, as well as to determine the existence of self-similar scaling laws and the critical value of Reynolds number and length scales necessary for transition to occur in these extreme mixing environments. Experiments conducted as part of this project will provide the first detailed turbulence statistics measurements (i.e., Reynolds stresses, density-velocity correlations and their spectra) for shock-accelerated variable density flows at M 2.0 and will inform physics-based models used in simulations by testing them under more realistic conditions. This research will help develop the capability to accurately predict and model extreme mixing, potentially leading to advances in a number of fields: energy, environment (atmospheric and oceanographic), aerospace engineering, chemical processing, homeland security and, most pertinently, inertial confinement fusion (ICF) devices. Broader Impacts: The integrated Education Plan will engage first-generation college students in experimental design and operation, support a woman graduate student to work on the proposed research, and use visualization and team-based approaches to improve students' understanding of concepts and promote communication and teamwork skills that are vital to success. The involvement of first generation students in research will lead to enhanced retention and success rates for these students in the department. An applet-based visual learning environment will enhance learning and retention of the material presented in class by allowing students to observe the dynamic phenomena and explore the effects of varying a parameter on the resulting solution. To increase awareness among the general public about shock-driven flows and their potential applications, we plan to work with a local high school teacher to create informational videos about our research and experimental facilities, post them on YouTube, and make them available to teachers for use in the classroom.