Experimental measurements for targeted assessments of turbulent shear flow mixing simulations

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。这些数据将支持亚网格尺度（SGS）湍流混合的大涡模拟（LES）的建模方法的发展。在大涡模拟中，混合的精确表示对于模拟非预混燃烧系统是至关重要的，其中分子混合是化学反应的必要前体。非常有限的测试SGS混合模型使用平面标量混合测量已被报道。在这里，粒子图像测速（PIV）和平面激光诱导荧光（PLIF）将产生气相湍流射流的速度和标量场的同时测量，而同时瑞利散射和PLIF将测量单和多物种标量混合。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，同时严格的数据简化确保了PLIF和瑞利散射结果的高精度。在气相中工作允许调查的速度和标量场长度尺度的范围内有关LES燃烧，从耗散尺度以及惯性范围。测量的平面性质允许反映LES中隐含的过滤的空间过滤。SGS混合模型性能的评价将包括先验检验，以及LES结果的适当的、网格相关的后验评估。这些后验测试将涉及，除了标度特性和平均配置文件的标准比较，LES捕获大规模流动组织的能力的评估，和真正的LES网格规模的波动，空间梯度和概率分布。研究结果将为理解SGS标量模型的性能提供一个严格的框架。这项工作将直接通知的努力，应用LES现实的燃烧系统，包括燃气涡轮机和内燃机（IC）发动机。创新的内燃机技术，如直接喷射，在燃油经济性方面提供了显着的收益，并随之减少了二氧化碳的产生。对实际发动机进行大涡模拟的能力将极大地促进其效率和排放控制的优化。这项工作也将在LES在地球物理问题上的努力中得到应用，例如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.