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

0933848 Adrian本研究将研究中等雷诺数、规范壁湍流中的涡流结构，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。现在清楚的是，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剪应力的一半以上。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相关外，还没有了解缓冲层、对数层和尾流中的涡如何与LSM和VLSM相关。我们描述三维结构的能力的另一个弱点是，一个统一的数学方法还没有被应用到全范围的规模和规范流的全套。因此，具体的目标是适应三维适当的正交分解（POD），以达到这一目的，并将其应用到三个流：管道，通道和边界层使用现有的直接数值模拟的数据。近壁面准流向涡的结构及其动力学正变得相当清楚。这项工作将使我们对对数层和大/超大尺度结构的理解建立在一个可比的基础上，并为解决这些运动的动力学奠定基础。将LSM/VLSM涡旋描述成一幅统一的图像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。更深入地了解POD模式及其在多尺度上与相干结构的关系，将大大推进我们从丰富的直接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尔-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。从广义上讲，这种改进在能源、运输、天气预报和其他地球物理过程等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.