Large-Eddy-Simulation Studies and In-situ Observations of Land Atmosphere Exchanges in Large Wind Farms

这项研究将开发和应用计算工具，以预测和了解超大型风电场中标量的通量，如热量和水分。这些通量在陆地-大气耦合以及陆地-大气界面因预期的全球风能增长而改变而可能产生的扰动中发挥了关键作用。目前，风电场的影响是在区域尺度和全球尺度模式中使用有效粗糙度长度来参数化的，有时还会因为尾迹而增加湍流动能。这种方法仍然以经典的大气边界层相似理论为基础。该理论假设地面是均匀的，但在非均匀特征的地面上的流动也经常被发现是可以接受的，例如由尾流和风力涡轮机的其他效应引起的非均匀。这是由于ABL中的湍流，有效地将各种来源和景观中的不均匀混合在一起。然而，这种参数化的适当性和所使用的参数的值是高度不确定的，特别是在一般大气条件(对流、稳定、中性)下的风电场的情况下。智力优势：相关的高分辨率数据将通过一系列适当选择的参数大涡模拟(LES)来产生，这些LES准确地量化了风力机阵列下方地表预期的陆地-大气感热和水汽交换。模拟将涵盖广泛的大气条件(中性、对流、稳定)和风电场布置(涡轮机间距、地面特性、负载系数)。在相当理想和可管理的条件下获得的计算结果将与风电场的现场观测相补充。实地研究将通过与瑞士研究人员的国际合作进行，这些研究人员可以访问西班牙萨拉戈萨附近的La Muela风力发电场。经过验证的模拟结果将被分析，其具体目的是推导包括风力涡轮机阵列在内的大气边界层的新的Monin-Obukhov类型关系。例如，修正的稳定性修正和修正的有效标量粗糙度长度将作为相关参数的函数得到。这项研究的结果将能够更准确地预测大范围风电场可能的反馈机制，包括当地和区域的气象条件、区域尺度的蒸发等。随着计算模拟的出现，人们对人为改变地表对陆地-大气相互作用的影响有了更多的了解。风能作为可再生能源组合的重要贡献者的增长表明，美国和世界陆地表面不可忽视的部分最终可能被用于大型风力发电场。预测和更好地了解在这种条件下陆地和大气耦合的物理过程是一个非常及时和关键的研究领域。研究生教育和培训将强调模拟、参数化和现场实验活动之间的相互作用。招聘和教育外展将利用综合研究生教育和研究培训(IGERT)对复杂系统进行建模，以及PI通过在波多黎各的联系人招聘美国拉美裔研究生的持续努力。通过为初中生或高中生提供研究经验，PI将积极继续与巴尔的摩当地一所高中进行的接触。

The study will develop and apply computational tools for predicting and understanding fluxes of scalars such as heat and moisture in very large wind farms. These fluxes play a crucial role in the land-atmosphere couplings and in possible perturbations stemming from modifications of the land-atmosphere interface with the anticipated global growth of wind energy. At present, effects of wind farms are parameterized in regional scale and global scale models using effective roughness lengths and, sometimes, increased turbulence kinetic energy due to wakes. Such approaches continue to be based on classical similarity theory of the atmospheric boundary layer (ABL). The theory assumes a uniform land surface yet has also often been found acceptable in flows over heterogeneous features of the land surface such as heterogeneities induced by wakes and other effects from wind turbines. This is due to the turbulent flow in the ABL, which efficiently blends the various sources and inhomogeneities across the landscape. However, the appropriateness of such parameterizations, and the values of parameters to be used, are highly uncertain especially in the case of wind farms under general atmospheric conditions (convective, stable, neutral).Intellectual merit:The relevant high-resolution data will be generated via a series of suitably chosen parametric Large-Eddy-Simulations (LES) that quantify accurately the land-atmosphere exchanges of sensible heat and moisture to be expected at the ground surface, underneath wind turbine arrays. These LES resolve significant portions of the individual wakes behind wind turbines and the concomitant modifications to mixing and entrainment.The simulations will cover a wide range of atmospheric conditions (neutral, convective, stable) and wind farm arrangements (turbine spacings, ground properties, loading factors). The computational results obtained under fairly idealized, and thus manageable, conditions will be complemented with in-situ observations in a wind farm. Field studies will take place through an international collaboration with researchers in Switzerland who have access to the La Muela wind farm near Zaragoza in Spain. The results of the validated simulations will be analyzed with the specific purpose of deriving new Monin-Obukhov-type relationships for atmospheric boundary layers including wind turbine arrays. For instance, modified stability corrections and modified effective scalar roughness lengths will be derived as function of relevant parameters. The results of this study will enable more accurate prediction of possible feedback mechanisms of extensive wind farms with local and regional meteorological conditions, regional scale evaporation, etc.Broader impacts: Regional scale surface fluxes of momentum, sensible heat and water vapor play a crucial role in quantifying and understanding the water and energy cycles at various spatial and temporal scales. With the advent of computational modeling, there has been much increased understanding of the effects of manmade modifications to the land surface on land-atmosphere interactions. The growth of wind energy as an important contributor to the renewable energy portfolio suggests the possibility that non-negligible portions of the land surface of the U.S. and the world may ultimately be used for large wind farms. Predicting and better understanding the physical processes coupling the land and atmosphere under such conditions is a very timely and critical area of research.Graduate education and training will stress the interplay between simulation, parameterization, and in-situ field experimental campaigns. Recruiting and educational outreach will leverage an Integrative Graduate Education and Research Traineeship (IGERT) on modeling complex systems and the PI's ongoing efforts to recruit U.S. Hispanic graduate students through contacts in Puerto Rico. The PI's ongoing outreach to a local Baltimore high-school will be actively continued by providing research experiences for junior or senior high-school students.