Experimental measurements for targeted assessments of turbulent shear flow mixing simulations

su0854402本研究将应用平面激光成像技术对湍流、轴对称射流和旋转射流中的速度场和标量场进行高度定量的测量。这些数据将为大涡湍流混合模拟的亚网格尺度（SGS）建模方法的发展提供支持。分子混合是化学反应的必要前提，因此精确表征LES中的混合对于模拟非预混燃烧系统至关重要。使用平面标量混合测量的SGS混合模型进行了非常有限的测试。在这里，粒子图像测速（PIV）和平面激光诱导荧光（PLIF）将同时测量气相湍流射流中的速度场和标量场，而同时瑞利散射和PLIF将测量单种和多种标量混合。对标准互相关PIV算法的改进提高了速度和速度梯度测量的精度和分辨率，同时严格的数据缩减确保了PLIF和瑞利散射结果的高精度。在气相中工作，可以研究与燃烧LES相关的速度范围和标量场长度范围，从耗散范围到惯性范围。测量的平面特性允许空间滤波，这反映了LES中隐含的滤波。对SGS混合模型性能的评价将包括先验测试，以及对LES结果进行适当的、依赖于网格的后验评估。除了尺度特性和平均剖面的标准比较之外，这些后验测试还包括LES捕捉大规模流动组织的能力的评估，以及真正的LES网格尺度波动、空间梯度和概率分布。这些结果将为理解SGS标量模型的性能提供一个严格的框架。这项工作将直接指导将LES应用于实际燃烧系统的努力，包括燃气轮机和内燃机。创新的集成电路发动机技术（如直喷）显著提高了燃油经济性，并减少了二氧化碳的排放。对实际发动机进行低碳排放的能力将极大地促进其效率和排放控制的优化。这项工作还将应用于LES在地球物理问题上的努力，例如那些涉及大气和海洋中的运输和混合的问题。

Su0854402This study will apply planar laser imaging techniques to perform highly quantitative measurements of velocity and scalar fields in turbulent, axisymmetric jet and swirling jet flows. The data will support the development of subgrid-scale (SGS) modeling approaches for large-eddy simulations (LES) of turbulent mixing. Accurate representation of mixing in LES is crucial to efforts to simulate non-premixed combustion systems, where molecular mixing is a necessary precursor to chemical reaction. Very limited tests of SGS mixing models using planar scalar mixing measurements have been reported. Here, particle image velocimetry (PIV) and planar laser-induced fluorescence (PLIF) will yield simultaneous measurements of velocity and scalar fields in gas-phase turbulent jets, while simultaneous Rayleigh scattering and PLIF will measure single- and multi-species scalar mixing. Refinements to standard cross-correlation PIV algorithms improve the accuracy and resolution of the velocity and velocity gradient measurements, while strict data reduction ensures high accuracy of the PLIF and Rayleigh scattering results. Working in the gas phase allows the investigation of a range of velocity and scalar field length scales relevant to LES of combustion, from the dissipation scales well into the inertial range. The planar nature of the measurements permits spatial filtering that reflects the filtering implicit in LES. Evaluations of SGS mixing model performance will include a priori tests, as well as appropriate, grid-dependent, a posteriori assessments of LES results. These a posteriori tests will involve, besides standard comparisons of scaling properties and mean profiles, assessment of the ability of LES to capture large-scale flow organization, and true LES grid-scale fluctuations, spatial gradients, and probability distributions. The results will provide a rigorous framework for understanding the performance of SGS scalar models. This work will directly inform efforts to apply LES to realistic combustion systems, including gas turbine and internal combustion (IC) engines. Innovative IC engine technologies, such as direct injection, offer significant gains in fuel economy, and attendant reductions in carbon dioxide production. The ability to perform LES of practical engines will greatly facilitate the optimization of their efficiency and emission control. The work will also find applications in LES efforts in geophysical problems, such as those involving transport and mixing in the atmosphere and oceans.