Quantitative Gas-Phase Scalar Mixing Measurements in Turbulent Spray Flows

湍流喷雾流中的定量气相标量混合测量

• 批准号: 1067625
• 负责人: Jeffrey Sutton
• 金额: $ 28.04万
• 依托单位: Ohio State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2011
• 资助国家: 美国
• 起止时间: 2011-06-01 至 2016-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1067625&HistoricalAwards=false
• 关键词: Quantitative; Gas; Phase; Scalar; Mixing

1067625SuttonFor the majority of practical energy-conversion systems, a liquid fuel spray is injected into an oxidizing environment; where the liquid droplets must disperse, evaporate, and the fuel vapor must molecularly mix with the oxidizer prior to chemical reaction. Although complicated by several physical and chemical processes, liquid-fueled combustors are ultimately limited by droplet vaporization and the subsequent gas-phase mixing process. While scalar mixing has been studied in-depth for single-phase turbulent flows, the current understanding of gas-phase mixing processes within turbulent sprays is limited due to the scarcity of experimental evaluation. This primarily stems from the extreme difficulty of accurately measuring vapor-phase concentrations in the presence of droplets. The objective of this research is the development, validation, and application of a new laser-based imaging diagnostic to experimentally investigate vaporization and gas-phase mixing processes in turbulent spray flows. Intellectual Merit: The current research program will involve the development of a variation of the Filtered Rayleigh Scattering (FRS) technique to accurately image fuel-vapor concentration fields without interference from the surrounding liquid-phase droplets. This research program is underpinned by a systematic assessment of the accuracy, sensitivity, and limitations of the proposed FRS technique as applied in turbulent spray flows. The new FRS approach offers the potential for two distinct advantages compared to previous techniques for detecting fuel vapor in the presence of droplets: (1) due to the nature of FRS, the recorded signal can be unambiguously due to vapor because the light scattering from the unwanted liquid-phase droplets can be spectrally-filtered using the combination of a single-frequency laser source and an optically-thick atomic or molecular filter. The gas-phase scattering of interest is spectrally-broadened due to thermal Doppler effects and a portion of this broadened gas-phase information falls outside of the molecular filter's bandwidth and is successfully transmitted to a detector. (2) The FRS technique does not require a particular fluorescent fuel or tracer, rather it takes advantage that the majority of fuels have large Rayleigh scattering cross sections and the recorded signal is dependent on the local composition of the fuel vapor and air mixture. By not using fluorescent fuel tracers, complications due to distillation effects are avoided. Once validated, the new tool will be applied to understand the coupling between droplet dispersion, vapor production, and gas-phase (fuel vapor and air) mixing in turbulent evaporating sprays. The proposed diagnostic approach will be transformative as a new, fundamental level of understanding of the vaporization and mixing processes found within multi-phase systems will result from the development of this diagnostic, allowing access to previously unavailable gas-phase processes embedded within the liquid spray. It is also anticipated that new fundamental measurements in turbulent sprays will prove invaluable to the modeling communityBroader Impacts: Proper fuel-air mixture preparation is critical for meeting performance objectives of modern energy-conversion systems including controlled ignition, flame stability, efficiency, and low pollutant emissions. The proposed FRS technique offers the opportunity to acquire a new, fundamental level of understanding of the complex vaporization and turbulent mixing processes that is needed as a building block to understand the highly turbulent, multiphase conditions found in realistic engines. An improved fundamental understanding offers the opportunity for more efficient and controlled combustion within practical platforms. In terms of research-related education, the Ph.D. research of a graduate student will be supported by this project. This research provides unique opportunities for direct teaching and training and allows the graduate student to work within (and significantly contribute to) a wide range of advanced topics including fluid dynamics and optical diagnostics. This project also will involve the participation of undergraduate student researchers, providing an opportunity to expose the brightest undergraduates to graduate-level research and thus helping to extend the pool of qualified graduates within the scientific and technological community. Additional contributions to the national and international academic and research infrastructure will be made through the dissemination of results into the open literature, and through presentations at conferences. Additional contributions to the educational infrastructure will be made by integrating the research efforts into teaching at the graduate level.

对于大多数实用的能量转换系统，液体燃料喷雾被注入到氧化环境中；在氧化环境中，液滴必须分散、蒸发，燃料蒸汽必须在化学反应之前以分子形式与氧化剂混合。尽管液体燃料燃烧器有几个复杂的物理和化学过程，但最终还是受到液滴蒸发和随后的气相混合过程的限制。虽然单相湍流标量混合已经被深入研究，但由于缺乏实验评价，目前对湍流喷雾内的气相混合过程的了解是有限的。这主要源于在存在液滴的情况下准确测量气相浓度的极端困难。这项研究的目的是开发、验证和应用一种新的基于激光的成像诊断方法来实验研究湍流喷雾流动中的汽化和气相混合过程。智能优点：目前的研究计划将涉及开发一种滤波瑞利散射(FRS)技术的变体，以准确地成像燃料蒸汽浓度场，而不会受到周围液滴的干扰。这项研究计划的基础是对建议的FRS技术在湍流喷雾流动中应用的准确性、敏感性和局限性进行了系统的评估。与以前用于检测存在液滴的燃料蒸气的技术相比，新的FRS方法具有两个明显的优势：(1)由于FRS的性质，记录的信号可以明确地归因于水蒸气，因为来自不需要的液滴的光散射可以使用单频激光光源和光学厚度的原子或分子滤光片组合进行光谱过滤。由于热多普勒效应，感兴趣的气相散射被光谱展宽，并且这种展宽的气相信息的一部分落在分子滤光器的带宽之外，并被成功地传输到探测器。(2)FRS技术不需要特定的荧光燃料或示踪剂，而是利用了大多数燃料具有较大的瑞利散射截面，并且记录的信号取决于燃料蒸汽和空气混合物的局部组成。由于不使用荧光燃料示踪剂，避免了由于蒸馏效应而导致的并发症。一旦得到验证，新工具将被用于了解湍流蒸发喷雾中液滴分散、蒸汽产生和气相(燃料蒸汽和空气)混合之间的耦合。拟议的诊断方法将是变革性的，因为这种诊断方法的发展将使人们对多相系统内的汽化和混合过程有一个新的、基本的了解，使人们能够接触到以前无法获得的嵌入在液体喷雾中的气相过程。还预计，湍流喷雾中的新基本测量将被证明对模型界非常有价值：适当的燃料-空气混合物制备对于实现现代能源转换系统的性能目标至关重要，这些目标包括受控点火、火焰稳定性、效率和低污染物排放。拟议的FRS技术提供了一个机会，让我们有机会对复杂的汽化和湍流混合过程有一个新的、基本的了解，这是理解现实发动机中存在的高度湍流、多相条件所需的基础。更好的基本理解为在实际平台中更有效和更可控的燃烧提供了机会。在研究型教育方面，该项目将支持一名研究生的博士研究。这项研究为直接教学和培训提供了独特的机会，并允许研究生在包括流体动力学和光学诊断学在内的广泛的高级主题中工作(并做出重大贡献)。该项目还将有本科生研究人员参与，使最聪明的本科生有机会从事研究生水平的研究，从而帮助扩大科技界的合格毕业生队伍。将通过在公开文献中传播成果和在会议上发言，为国家和国际学术和研究基础设施作出更多贡献。将把研究工作纳入研究生一级的教学，从而为教育基础设施作出更多贡献。