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

1336761 suttn这个项目的目标是量化由湍流运动控制被动标量混合的多尺度动力学。具体来说，流体湍流和气相剪切流中标量场之间的时间和尺度依赖性耦合将通过同时高速（10 kHz采集率）3D速度和2D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，已经成为60多年来的研究课题；然而，产生观察到的现象的潜在物理和控制机制仍然不清楚。湍流本质上是间歇性的、多维的现象，它创造了一个高度动态的系统，发生在多个长度和时间尺度上。此外，标量输运可能以一种时空复杂的方式与高度非线性的速度场耦合。这不仅会导致在开发可处理的理论描述方面的困难，而且还会导致开发鲁棒性和预测性计算建模能力的困难。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场性质。该项目将得益于定量高速成像的最新技术进步，特别是一种新的多千赫高能激光系统，该系统可以同时在高雷诺数气相流中进行时间分辨3D速度和2D守恒标量测量。该项目将通过实时表征湍流速度和标量场之间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。这些测量结果将用于研究控制所谓“斜坡-悬崖”形成的潜在机制，这表明在较小尺度上存在大规模间歇性的印记，而在所有尺度上都存在持续的标量各向异性。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，表征每个过程的间歇性水平。基于时间的关节速度标量统计将允许速度混合动力学性质的新参数化。此外，还建议通过实验确定新的多点多时间相关性，这些相关性是包含空间和时间结构信息的统计量，可以与大涡模拟（LES）的理论和时间相关建模结果进行适当的比较。更广泛的影响：一个成功的项目将对湍流中标量混合的基本理解和一般湍流领域产生重大影响。由于大多数实际燃烧系统（如燃气轮机和内燃机）的性能都是由湍流混合支撑的，因此更好地理解底层物理可以导致更清洁、更高效的系统。拟议的研究还将提供关键的新数据来评估湍流理论，并开发基于物理的LES模型，以及它们在现实湍流环境中的实施。在与研究相关的教育方面，本项目将支持一名博士生。将尽一切努力使传统上被归类为代表性不足的学生，包括妇女和少数民族的学生参与进来。通过本科生荣誉项目、研究研讨会、将成果传播到公开文献中，以及通过在会议上发表演讲，可以获得更广泛影响的额外机会。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.