Unified description of the three-dimensional structure of wall-turbulence

0933848Adrian本研究将研究中等雷诺数、正则壁面湍流中的涡旋结构，目的是建立一个统一的物理-数学描述，包括从近壁到超大尺度运动的所有尺度。很明显，大尺度和超大尺度运动(LSM和VLSM)发生在所有壁面流动中，并占外层湍流动能和雷诺切应力的一半以上。但是，人们对它们的形态知之甚少，对它们的起源更是知之甚少。除了一些证据表明它们与小的近壁涡旋相关外，还不清楚缓冲层、对数层和尾迹中的涡旋是如何与LSM和VLSM相关的。我们描述三维结构的能力的另一个弱点是，还没有一个统一的数学方法应用于所有范围的尺度和全套规范流。因此，我们的具体目标是利用现有的直接数值模拟数据，将三维本征正交分解(POD)应用于三种流动：管流、槽流和边界层。近壁中准流向涡旋的结构及其动力学正变得相当清楚。这项工作将使我们在可比较的基础上理解对数层和大/超大尺度的结构，并为解决这些运动的动力学问题奠定基础。将LSM/VLSM涡旋合并到一张统一的图片中，将回答一个长期存在的问题，即近壁层的自主性和决定统计行为的物理过程。深入理解POD模式及其与多尺度相干结构的关系，将极大地促进我们从丰富的Direct Navier Stokes模拟数据库中提取信息的方法。它还将影响大涡模拟和雷诺平均纳维斯托克斯计算方法的制定，以及工程系统的标度律和减少阻力和以其他方式管理表面湍流的技术的制定。非常广泛地说，这种改进在能源、交通、天气预报和其他地球物理过程领域对社会具有价值。

0933848AdrianThis research will investigate the structure of eddies in moderate Reynolds number, canonical wall turbulence for the purpose of developing a unified physical-mathematical description including all scales ranging from the near- wall to the very large-scale motions. It is now clear that large- and very-large-scale motions (LSM and VLSM) occur in all wall flows and account for more than one-half of the turbulent kinetic energy and Reynolds shear stress in the outer layer. But, very little is known about their form, and even less about their origins. Aside from some evidence that they are correlated with the small, near-wall eddies, there is no understanding of how eddies in the buffer layer, the logarithmic layer, and the wake are related to the LSM and the VLSM. The other weakness in our ability to describe the three-dimensional structure is that a unified mathematical methodology has yet to be applied to the full range of scale and the full set of canonical flows. The specific goals are therefore to adapt three-dimensional proper orthogonal decomposition (POD) to this purpose and apply it to three flows: pipe, channel and boundary-layer using data from existing direct numerical simulations. The structure of quasi-streamwise vortices in the near-wall and their dynamics are becoming reasonably well understood. This work would put our understanding of the structure of the logarithmic layer and large/very-large scale on a comparable footing, and establish a basis for addressing the dynamics of these motions. Incorporating the LSM/VLSM eddies into a unified picture will answer a long-standing question concerning autonomy of the near-wall layer and the physical processes that determine the statistical behavior. Deeper understanding of POD modes and their relation to coherent structures on multiple scales will materially advance our methodology for extracting information from the richness of Direct Navier Stokes simulation databases. It would also impact the formulation of large eddy simulations and Reynolds Averaged Navier Stokes computational methods, and scaling laws for engineering systems and the formulation of techniques to reduce drag and otherwise manage turbulent flow over surfaces. Very broadly, such improvements have value to society in the areas of energy, transportation, weather prediction and other geophysical processes.