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测量。这些数据将为发展用于湍流混合的大涡模拟(LES)的亚网格尺度(SGS)模拟方法提供支持。对于分子混合是化学反应的必要先导的非预混燃烧系统的模拟来说，大涡模拟中混合的准确表示是至关重要的。使用平面标量混合测量对SGS混合模型进行的测试非常有限。其中，粒子图像测速仪(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将测量单组分和多组分的标量混合。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，同时严格的数据处理确保了PLIF和瑞利散射结果的高精度。在气相中工作允许研究与燃烧大涡相关的一系列速度和标量场长度尺度，从耗散尺度到惯性范围。测量的平面性质允许反映LES中隐含的过滤的空间过滤。对SGS混合模型性能的评估将包括先验测试，以及适当的、依赖于网格的对LES结果的后验评估。这些后验检验除了标度特性和平均剖面的标准比较外，还将涉及对大涡模拟捕捉大尺度流动组织的能力的评估，以及真实大涡模拟网格尺度的波动、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(IC)发动机。创新的内燃机技术，如直接喷射，可显著提高燃油经济性，并随之而来的二氧化碳排放减少。实际发动机执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。这项工作还将在地球物理问题的大涡模拟工作中得到应用，例如涉及大气和海洋中的输送和混合的问题。

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.