论文标题
改进的边缘区域技术，用于代表大涡模拟中的重力波，并应用于风电场
An improved fringe-region technique for the representation of gravity waves in large-eddy simulation with application to wind farms
论文作者
论文摘要
大气边界层的大涡模拟通常使用伪谱法进行，该方法采用边缘区域方法引入流入边界条件。但是，我们注意到，当考虑分层气氛时，标准的边缘区域技术会激发伪重力波，从而增强了从域顶的顶部反射的能量，并扰乱了下游的速度和压力场。在这项工作中，我们开发了一种新的边缘区域方法，该方法施加了流入条件，同时限制了对周围流动的虚假影响。这是通过在垂直动量方程中局部抑制对流项来实现的。我们首先将标准和无波的边缘区域技术应用于受169个不同大气状态的二维无关流量模拟。使用几个大气状态在三维领域进行了类似的研究。在所有情况下，新的边缘区域技术都均优于标准方法，从而施加流入条件，对周围流动的影响最小。此外，我们还研究了两个已经存在的非反射上边界条件的性能，即瑞利阻尼层（RDL）和辐射条件（RC）。结果突出了仔细调整RDL以限制数值解决方案的失真的重要性。另外，我们发现调整后的RDL在所有情况下都胜过RC。最后，将调谐的RDL与无波纹区域方法一起应用于在常规中性边界层中运行的风电场的LE，为此我们仅测量仅0.75％的反射率。
Large-eddy simulations of the atmospheric boundary layer are often performed using pseudo-spectral methods, which adopt a fringe-region approach to introduce inflow boundary conditions. However, we notice that a standard fringe-region technique excites spurious gravity waves when stratified atmospheres are considered, therefore enhancing the amount of energy reflected from the top of the domain and perturbing the velocity and pressure fields downstream. In this work, we develop a new fringe-region method that imposes the inflow conditions while limiting spurious effects on the surrounding flow. This is achieved by locally damping the convective term in the vertical momentum equation. We first apply the standard and wave-free fringe-region techniques to two-dimensional inviscid-flow simulations subjected to 169 different atmospheric states. A similar study is performed on a three-dimensional domain using a couple of atmospheric states. In all cases, the new fringe-region technique outperforms the standard method, imposing the inflow conditions with a minimal impact on the surrounding flow. Moreover, we also investigate the performance of two already existing non-reflective upper boundary conditions, that is a Rayleigh damping layer (RDL) and a radiation condition (RC). Results highlight the importance of carefully tuning the RDL to limit the distortion of the numerical solution. Also, we find that the tuned RDL outperforms the RC in all cases. Finally, the tuned RDL together with the wave-free fringe-region method are applied to an LES of a wind farm operating in a conventionally neutral boundary layer, for which we measure a reflectivity of only 0.75%.
