Multi-Scale Fluid Turbulence-Scalar Mixing Dynamics in Gas-Phase Turbulent Jets

1336761 Sutton本项目的目的是量化的多尺度动力学的被动标量的湍流运动的混合。 具体而言，时间和尺度相关的耦合流体湍流和气相剪切流内的标量场将同时高速（10 kHz采集速率）的三维速度和二维守恒标量成像进行研究。 湍流标量混合在自然界和工程过程中普遍存在，并且已经成为研究的主题超过60年;然而，产生所观察到的现象的基本物理和管理机制仍然不清楚。 湍流本质上是间歇性的、多维的现象，其产生在多个长度和时间尺度上发生的高度动态的系统。 此外，标量输运可能以空间和时间复杂的方式耦合到高度非线性的速度场。 这不仅导致难以开发易于处理的理论描述，而且也难以开发鲁棒性和预测性的计算建模能力。 需要新的测量和分析工具来研究、理解和描述湍流标量混合过程的多尺度和多物理性质。 该项目将得到最近在定量高速成像方面的技术进步的帮助，特别是一种新的多kHz高能激光系统，该系统允许在高雷诺数气相流中同时进行时间分辨的3D速度和2D守恒标量测量。 该项目将通过表征湍流速度与标量场之间真实的动态相互作用而具有变革性。 流体运动学和标量梯度之间的空间和时间相关性将被量化。 这些测量将用于调查所谓的“斜坡悬崖”形成的基本机制，这表明在所有尺度上，大规模的不稳定性在较小尺度上和持久的标量各向异性上的印记。 最后，独特的数据集将能够调查平流和扩散作为时间函数的相对重要性，表征每个过程的不稳定程度。 基于时间的，联合速度标量统计将允许一个新的参数化的性质的速度混合动力学。 此外，它建议实验确定新的，多点，多时间的相关性，这是统计量包含空间和时间的结构信息，可以适当地比较理论和时间依赖的建模结果从大涡模拟（LES）。 更广泛的影响：一个成功的项目将有显着影响的基本理解标量混合在湍流流动和湍流领域的一般。 由于大多数实际燃烧系统（如燃气涡轮机和内燃机）的性能都是由湍流混合来支撑的，因此更好地理解底层物理可以导致更清洁和更高效的系统。 拟议的研究还将提供关键的，新的数据来评估湍流理论和开发基于物理的LES模型，以及它们的实施到现实的湍流环境。 在研究相关教育方面，该项目将支持一名博士生。 将尽一切努力让传统上被归类为代表性不足的学生，包括妇女和少数民族学生参加。 通过本科荣誉项目，研究研讨会，将结果传播到公开文献中，以及通过会议上的演讲，将有更多的机会产生更广泛的影响。 这项研究为学生参与者提供了很好的机会，可以在包括流体动力学和光学诊断在内的广泛的高级主题中工作（并做出重大贡献）。

1336761 SuttonThe objective of this project is to quantify the multi-scale dynamics governing the mixing of a passive scalar quantity by turbulent fluid motion. Specifically, the time- and scale-dependent coupling between fluid turbulence and the scalar field within gas-phase shear flows will be investigated with simultaneous high-speed ( 10 kHz acquisition rate) 3D velocity and 2D conserved scalar imaging. Turbulent scalar mixing is ubiquitous in nature and engineering processes and has been a subject of research for more than sixty years; however, the underlying physics and governing mechanisms producing the observed phenomenology remain unclear. Turbulent flows are inherently intermittent, multi-dimensional phenomena, which create a highly dynamic system occurring on multiple length and time scales. In addition, scalar transport is likely coupled to the highly non-linear velocity field in a spatially and temporally complex manner. This not only leads to difficulties in developing tractable theoretical descriptions, but also to difficulties developing robust and predictive computational modeling capabilities. New measurement and analysis tools are needed to investigate, understand, and describe the multi-scale and multi-physics nature of the turbulent scalar mixing process. This project will be aided by recent technological advances in quantitative high-speed imaging and in particular, a new multi-kHz, high-energy laser system, which allows simultaneous time-resolved 3D velocity and 2D conserved scalar measurements in high-Reynolds number, gas-phase flows. The project will be transformative through characterization of the dynamic interaction between turbulent velocity and scalar fields in real time. Space- and time-correlation between fluid kinematics and scalar gradients will be quantified. The measurements will be used to investigate the underlying mechanisms governing the so-called "ramp-cliff" formation, which indicates the imprint of large-scale intermittency on smaller scales and persistent scalar anisotropy at all scales. Finally, the unique data sets will enable an investigation into the relative importance of advection and diffusion as a function of time, characterizing the level of intermittency of each process. Temporally based, joint velocity-scalar statistics will allow a new parameterization of the nature of velocity-mixing dynamics. In addition, it is proposed to experimentally determine new, multi-point, multi-time correlations, which are statistical quantities containing both spatial and temporal structural information that can be appropriately compared to both theory and time-dependent modeling results from large-eddy simulation (LES). Broader Impacts: A successful project will have significant impact on the fundamental understanding of scalar mixing in turbulent flows and in the field of turbulence in general. Since the performance of the majority of realistic combustion systems such as gas turbine and internal combustion engines are underpinned by turbulent mixing, a better understanding of the underlying physics can lead to cleaner and more efficient systems. The proposed research also will provide critical, new data to assess turbulence theory and to develop physically based LES models as well as their implementation into realistic turbulent environments. In terms of research-related education, a doctoral student will be supported by this project. Every effort will be made to include the participation of students traditionally classified as under-represented including women and minorities. Additional opportunities for broader impacts will be available through undergraduate honors projects, research seminars, the dissemination of results into the open literature, and through presentations at conferences. This research provides excellent opportunities student participants to work within (and significantly contribute to) a wide range of advanced topics including fluid dynamics and optical diagnostics.