Large-eddy simulations of complex turbulent flows

湍流发生在大多数流体流动中。它的复杂性是由于湍流输送主要是由于相干的，螺旋状的运动（“漩涡”），这是确定性的，但出现在随机的时间和地点。湍流输送在确定例如飞机的阻力或热交换器中的热传递方面起主要作用。明确解决涡流的解决方法越来越受欢迎，因为可以分析流动的更高精度和完整性;其中之一是大涡模拟（LES）。这项建议的重点是，首先，改进模型和方法的LES的发展，以减少其计算需求，并加快其过渡到工业;第二，LES的应用程序复杂的流动。 我的小组最近开发了一个新的模型来参数化小漩涡[Piomelli等人，流体力学杂志，766：499-527，2015]，其在初始测试中已经显示出其自身比现有模型准确并且计算上更便宜。我们建议修改它，以更好地响应当地的湍流状态，并将其扩展到更现实的流动。此外，我们将致力于发展一个“最佳LES”，其中计算网格适应流动，使网格大小的比例湍流的特征长度尺度是均匀的。这种改进有可能降低模拟的成本的数量级，因为目前的应用程序使用的网格，在某些地区过于精细和边际在其他地区。 第二个主题是LES的应用程序的技术相关性的问题，其中更详细的了解流物理，LES提供相比，其他技术可以导致显着的好处。首先，我们将研究粗糙度对热传递的影响，并探索未知的机制，确定能量的传输，为什么与动量传输的类比不成立时，粗糙度存在，以及如何模拟它。其次，我们将调查流动的河流沙丘，我们以前的研究扩展到现实生活中的配置，包括沙的运动和沙丘的动力学演化。最后，我们将应用大涡模拟来研究前缘突起物如何影响机翼的性能，以及哪些形状可以改善机翼的空气动力学性能和声音发射。 总之，这项建议将采取双管齐下的办法，协调方法改进、基础研究和应用。模型开发旨在显著降低计算成本，基础研究和应用将使用LES的增强功能来理解复杂的，以前无法解决的物理问题。这一建议还将导致培训至少四名HQP。

Turbulence occurs in most fluid flows. Its complexity is due to the fact that turbulent transport is mostly due to coherent, whorl-like motions (“eddies”), which are deterministic in character, but appear at random times and locations. Turbulent transport plays the primary role in determining, for instance, the drag of an aircraft or the heat transfer in a heat exchanger. Solution methods in which the eddies are explicitly resolved are gaining popularity because of the higher accuracy and completeness with which the flow can be analyzed; among them is the large-eddy simulation (LES). This proposal will focus, first, on the development of improved models and methodologies for LES, to decrease its computational demands and accelerate its transition to industry; second, on the application of LES to complex flows. My group has recently developed a new model to parameterize the small eddies [Piomelli et al., J. Fluid Mech., 766:499-527, 2015], which, in initial tests, has shown itself to be accurate and computationally cheaper than existing models. We propose to modify it to respond better to the local state of the turbulence, and extend it to more realistic flows. Furthermore, we will work towards the development of an "optimal LES" in which the computational grid adapts to the flow so that the ratio of grid size to the characteristic length-scale of turbulence is uniform. This improvement has the potential of decreasing the cost of a simulation by orders of magnitude, since present applications use grids that are overly refined in some regions and marginal in others. The second theme is the application of LES to problems of technological relevance, in which the more detailed understanding of the flow physics that LES affords in comparison to other techniques can result in significant benefits. First, we propose to study the effect of roughness on heat transfer, and explore the unknown mechanisms that determine the transport of energy, why the analogy with the transport of momentum does not hold when roughness is present, and how to model it. Second, we will investigate the flow over river dunes, extending our previous research to real-life configurations, including the sand motion and the dynamical evolution of the dune. Finally, we will apply LES to study how leading-edge protuberances can affect the performance of wings, and which shapes can improve the aerodynamic behaviour and sound emission of the wing. In summary, this proposal will take a two-pronged approach that coordinates methodological improvements, fundamental studies and applications. The model development is designed to decrease significantly the cost of the calculations, and the fundamental studies and applications will use the increased capabilities of LES to understand the physics of complex, previously unapproachable, problems. This proposal will also result in the training of at least four HQP.