CAREER: A New Understanding of Flame Dynamics and Turbulence-Chemistry Interaction from 2D/3D/4D Spatio-Temporal Measurements

本研究的目的是量化湍流火焰中高度非定常流场、物质浓度、局部温度和反应速率之间的随时间耦合。湍流本质上是时变的三维现象，当与化学反应相结合时，就会形成一个高度动态的系统，发生在多个长度和时间尺度上。湍流燃烧动力学还没有得到很好的理解，这限制了先进控制策略和工程应用预测数值模型的发展。目前的燃烧模型很难准确地预测波动湍流流场、反应性标量混合和复杂火焰化学在广泛条件下的时间依赖关系。在这项研究计划下进行的测量将解决空间和时间上的物理和化学过程，并将用于评估时间相关燃烧模型中的常见假设，并指导未来的方法。了解湍流燃烧环境的时间和空间行为对改进现代能量转换系统至关重要。智力优势：拟议的研究植根于一种新的多维、高重复率（10 kHz）激光诊断测量，这些测量的速度、温度、物质浓度和反应速率是以前没有的。湍流火焰中的标量传输和混合，以及单个湍流-化学相互作用将被“实时”跟踪。具体的研究贡献包括完全解析的四维（三维空间和时间）温度和物质浓度梯度，用于分析大尺度湍流输运与小尺度混合和化学反应之间的竞争。在不同的流动条件下，将确定速度场和多个反应标量场的时空相关性以及控制长度和时间尺度。同时进行的高速速度和标量测量将及时得出流动-火焰相互作用，详细说明物质输运、湍流混合和局部反应速率如何被波动湍流修改并与波动湍流耦合。最后，从速度/标量测量中获得的新的时间数据和统计数据（例如波动、相关性、时间尺度和功率谱）将作为大涡模拟（LES）模型的改进评估工具。PI将通过湍流非预混火焰测量和计算国际研讨会与桑迪亚国家实验室的研究人员和同事合作，评估、验证和改进当前LES方法的预测能力。更广泛的影响：一个成功的项目将导致对燃烧动力学的新理解，这将对预测燃烧模型的发展产生重大影响，并可能导致在高瞬态环境下改善燃烧控制。这两个因素都有可能提高燃烧系统的效率、火焰稳定性和污染物排放量。由于湍流燃烧过程占世界能源使用量的85%以上，因此提高效率和降低排放对环境可持续性和能源安全具有重要意义。该研究项目与一系列教育和推广活动紧密结合，有三个目标：(1)通过本地推广提高大学预科学生追求科学和工程职业的兴趣，(2)促进大学水平的主动学习（和教学），(3)提高学生形象化物理概念的能力，从而使个人学生更容易实现从理论到应用的过渡。外展计划的一个组成部分是，将在当地一所以硕士为基础的高中开发并提供一系列互动教学模块，该高中专门针对生活在高度贫困地区的学生提供基于stem的课程。这些模块旨在培养少数民族学生对科学和工程学科的兴趣，这些学生很少接触科学和数学为基础的职业。

The objective of this research is to quantify the time-dependent coupling among the highly unsteady flowfield, species concentrations, local temperature, and reaction rates in turbulent flames. Turbulent flows are inherently time-varying, three-dimensional phenomena, and when coupled with chemical reactions, create a highly dynamic system occurring on multiple length and time scales. Turbulent combustion dynamics are not well understood, which limits the development of both advanced control strategies and predictive numerical models for engineering applications. Current combustion models have difficulty in accurately predicting the time-dependent relationship between the fluctuating turbulent flowfield, reactive scalar mixing, and the complex flame chemistry over a broad range of conditions. Measurements performed under this research program will resolve physical and chemical processes in both space and time and will be used to assess common assumptions found in time-dependent combustion models and guide future approaches. Understanding both the temporal and spatial behavior of turbulent combustion environments is critical for improving modern energy-conversion systems. Intellectual Merit: The proposed research is rooted in a new class of multi-dimensional, high-repetition rate ( 10 kHz) laser diagnostic measurements of velocity, temperature, species concentrations, and reaction rates that have not been available previously. Scalar transport and mixing within turbulent flames, along with individual turbulence-chemistry interactions will be tracked in "real time". Specific research contributions include fully-resolved, four-dimensional (three spatial dimensions and time) temperature and species concentration gradients to analyze the competition between large-scale turbulent transport and small-scale mixing and chemical reaction. Space-time correlations and the governing length and time scales for the velocity and multiple reactive scalar fields will be determined under varying flow conditions. Simultaneous high-speed velocity and scalar measurements will yield flow-flame interactions in time, detailing how species transport, turbulent mixing, and local reaction rates are modified by and coupled to the fluctuating turbulence. Finally, new temporal data and statistics (e.g., fluctuations, correlations, time-scales, and power spectra) derived from the velocity/scalar measurements will serve as improved assessment tools for large-eddy simulation (LES) models. The PI will collaborate with researchers at Sandia National Laboratories and colleagues through the International Workshop on Measurement and Computation of Turbulent Non-Premixed Flames and to assess, validate, and improve the predictive capabilities of current LES approaches.Broader Impacts: A successful project will lead to a new understanding of combustion dynamics, which will have significant impact in the development of predictive combustion models and perhaps lead to improved combustion control within highly transient environments. Both of these factors have the potential to yield improvements in efficiency, flame stability, and pollutant output in combustion systems. Because turbulent combustion processes account for more than 85% of the world's energy usage, improvements in efficiency and lowered emissions have important implications in terms of environmental sustainability and energy security. The research program is heavily integrated into a series of educational and outreach activities with three objectives (1) increasing the interest of pre-college students in pursuing a career in science and engineering through local outreach, (2) fostering active learning (and teaching) at the collegiate level and (3) increasing students- ability to visualize physical concepts, thus making the transition from theory to application more achievable for the individual student. One component of the outreach plan is a series of interactive teaching modules will be developed and delivered at a local mastery-based high school which specializes in a STEM-based curriculum targeted for students living in high poverty areas. These modules are intended to cultivate interests in scientific and engineering disciplines within minority students who have had little exposure to science and math-based careers.