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

1336761问题本项目的目标是量化控制通过湍流运动混合被动标量的多尺度动力学。具体地说，在高速(10 kHz采集率)三维速度和二维守恒标量成像的同时，将研究气相剪切流动中流体湍流和标量场之间的时间和尺度耦合。湍流标量混合在自然界和工程过程中普遍存在，是六十多年来研究的主题；然而，产生所观察到的现象学的基本物理和支配机制仍然不清楚。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，标量输运很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。这不仅导致开发易于处理的理论描述的困难，而且也导致开发健壮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性质。该项目将得到定量高速成像技术最新进展的帮助，特别是一种新的多千赫高能激光系统，该系统可以在高雷诺数、气相流中同时进行时间分辨3D速度和2D守恒标量测量。该项目将通过实时描述湍流速度和标量场之间的动态相互作用来实现变革性。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。这些测量将被用来研究控制所谓的“斜坡-悬崖”形成的潜在机制，这表明在更小的尺度上存在大范围的间歇性，在所有尺度上都存在持续的标量各向异性。最后，独特的数据集将使我们能够调查平流和扩散作为时间函数的相对重要性，从而表征每个过程的间歇性程度。基于时间的联合速度标量统计将允许对速度混合动力学的性质进行新的参数化。此外，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结构信息和时间结构信息的统计量，可以与大涡模拟(LES)的理论和时间相关模拟结果进行适当比较。更广泛的影响：一个成功的项目将对湍流和整个湍流领域中标量混合的基本理解产生重大影响。由于大多数实际燃烧系统(如燃气轮机和内燃机)的性能都以湍流混合为基础，因此对基本物理的更好理解可以带来更清洁和更高效的系统。这项拟议的研究还将为评估湍流理论、发展基于物理的大涡模拟及其在现实湍流环境中的应用提供关键的新数据。在研究性教育方面，该项目将支持一名博士生。将尽一切努力包括传统上被归类为代表不足的学生的参与，包括妇女和少数群体。更多产生更广泛影响的机会将通过本科生荣誉项目、研究研讨会、将结果传播到公开文献中以及通过在会议上发表演讲来实现。这项研究为学生参与者提供了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(并对其做出重大贡献)的绝佳机会。

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.