High performance computing methodologies for solving complex turbulent flows

计算流体力学(CFD)方法通常被用作解决工业和环境工程问题的工具。由于这些问题大多是湍流的，因此湍流效果的逼真模拟是必不可少的。基于雷诺平均纳维斯托克斯(RANS)的方法已经成为计算湍流的主要方法，特别是在水力学和空气动力学中。然而，RANS模型已被发现对于具有大分离的复杂流动和需要考虑非定常效应的情况不够准确。计算机计算能力的提高和更精确、更高效的数值方法的发展导致了大涡模拟(LES)方法的发展。LES已被发现优于RAN，但过于昂贵，无法应用于实际规模的工程问题。一种更实惠的方法结合了RAN和LES的不同优势；人们只能在需要的地方使用LES，因为流量太复杂，而在域的其他部分，如靠近墙壁，流量是使用较便宜的RANS模型计算的。这被称为混合RANS-LES方法，对于现代CFD实践来说，这是一种有吸引力的方法。该研究计划致力于开发基于混合LERANS方法的高性能流动求解器，并研究现代数值方法，以实现高精度和高计算性能。更具体地说，我们将研究重叠网格和高阶离散化方法，以达到湍流所需的高精度。这些应用旨在解决水力学和空气动力学工程中遇到的复杂流动问题，例如溢洪道或大坝压力钢管上的自由表面流动，以及飞机结构周围的可压缩流动。

Computational fluid dynamics (CFD) methods are commonly used as tools for solving industrial and environmental engineering problems. As most of these problems are turbulent, the realistic simulation of the turbulence effect is essential. The Reynolds-Averaged Navier-Stokes (RANS)-based approach has become the workhorse for calculating turbulent flows, especially in hydraulics and aerodynamics. However, RANS models have been found to be not sufficiently accurate for complex flows with large separations and where unsteady effects are of interest. The increase in computer power and the development of more accurate and efficient numerical methods have led to the development of large eddy simulation (LES) methodology. LES has been found superior to RANS, but is too expensive to be deployed in real-scale engineering problems. A more affordable approach combines RANS and LES' different strengths; one can use LES only where needed because the flow is too complex, while in other parts of the domain, such as near walls, the flow is computed with the less expensive RANS model. This has become known as the hybrid RANS-LES approach, which is an appealing methodology for modern CFD practice. This research program is focused on the development of a high performance flow solver based on a hybrid LES-RANS approach and on the investigation of modern numerical methods to allow high accuracy and computational performance. More specifically, we will investigate overset-grid and higher-order discretizations methods to achieve the high accuracy required by turbulent flows. The applications are geared towards solving the complex flow problems encountered in hydraulics and in aerodynamics engineering, such as free surface flows over the spillways or the penstocks of dams, and compressible flows around aircraft structures.**