Tackling the global blockage problem in a wind-farm due to interactions between turbulent wakes

随着对全球气候和持续使用化石燃料的影响的日益关注，可再生能源最近受到了广泛关注。尽管如此，尽管取得了相当大的进展，但在充分利用风能方面仍然存在许多挑战。风力涡轮机通过从风中提取能量来产生可用的电力。这就产生了一个尾流，即紧接在涡轮机后面的一个缓慢移动的空气区域。一个涡轮机是好的，但为了满足我们在有限的陆地（或海洋）上的能源需求，我们需要许多精心布置的涡轮机（称为风力发电场）。这可能是一个问题，因为顺风涡轮机将位于上游涡轮机的尾流中。这种较低能量的尾流意味着由随后的涡轮机提取的能量较少，以及结构载荷增加，从而降低了能量产量并增加了成本。在风力工业中，考虑单个涡轮机并基于该单个涡轮机来确定特定地点处的风电场的性能通常是有用的。我们知道，当我们考虑风电场的性能时，必须考虑涡轮机的尾流。然而，这并不是全貌。随着风力发电场的安装增加，有关其运行的更多信息已经变得可用，并且已经确定了能源生产的赤字。这一赤字很小，但考虑到设计、建造和运营一个风力发电场20年的成本，这一小赤字可能导致重大的财务后果。直到最近，这一赤字的来源才被证明是微妙和难以捉摸的。风电场对发电量的影响比尾流的组合更为复杂。风电场本身的存在改变了风电场所在地遇到的风。风力发电场对风来说是一个障碍物，一个阻塞物，就像阻力最小路径的概念一样，风在某种程度上试图避开风力发电场。这表现为领先的迎风涡轮机以比没有风电场时更低的速度接收风。这被称为全球封锁。人们可以预料，全球封锁将引起学术界和工业界的极大兴趣，而事实上，这种兴趣已经得到。但这是以某种临时的方式完成的，侧重于问题的不同方面。该项目的性质是完成对全球阻塞的彻底和严格的调查，并确定和消除导致阻塞的风电场设计的主要恶化方面。风电场阻塞的精确定义和量化仍存在一定程度的不确定性，本项目必须从文献中确定或创建此类定义。这项研究将是实验性质的，在伦敦帝国理工学院的风洞中进行，即10英尺x 5英尺低速国家风洞设施。如前所述，阻塞损失的能量仅占风电场总能量产量的一小部分（约2%）。由于堵塞的影响如此之小，因此必须非常小心，以确保任何结果都能与测量不确定性区分开来。随着碳中和需求的增加和风能需求的增加，北海等高风力发电量地区的需求将越来越大。随着越来越多的农场被开发，全球封锁只会扮演越来越不那么微妙的角色。这项调查的潜在结果可能对未来风能项目的设计产生重要影响。阻塞的特征可以允许其减轻并增加能量产量，或者如果不能减轻，则可以更准确地了解特定风能项目的财务可行性。

With rising concerns about the global climate and the impact of continued use of fossil fuels, renewable sources of energy have received much attention of late. Despite this attention, and considerable progress, there remain many challenges to fully exploit the energy available in the wind. A wind turbine produces usable electricity by extracting energy from the wind. This produces a wake, an area of slower moving air immediately behind the turbine. One turbine is good, but to satisfy our energy needs on limited land (or sea) we need many carefully arranged turbines (called a wind farm). This can be a problem, as downwind turbines will sit in the wake of upstream turbines. This lower energy wake means there is less energy to be extracted by the following turbine(s), as well as increased structural loading, reducing energy yield and increasing costs. In the wind industry, it is often useful to think of an individual turbine and base the performance of the wind farm at a specific site on this individual turbine. We know that we must account for the wakes of the turbines when we account for the performance of the wind farm. This, however, is not the complete picture. With the increased installation of wind farms, more information about their operation has become available and a deficit energy production has been identified. This deficit is small, but considering the costs involved in designing, constructing and operating a wind farm for a period of 20 years this small deficit can result in significant financial consequences. The source of this deficit has proven to be subtle and elusive until recently. The influence of the wind farm on the energy yield is more complex than the combination of wakes. The presence of the wind farm itself changes the wind encountered at the wind farm's site. The wind farm acts as an obstacle, a blockage, to the wind, and like the concept of the path of least resistance, the wind in a manner tries to avoid the wind farm. This manifests itself as the leading upwind turbines receiving wind at a lower speed than they would in the absence of the wind farm. This is referred to as Global Blockage. One would expect that global blockage would be subject to considerable academic and industrial interest, which it indeed has received. But this has been completed in a somewhat ad hoc manner, focusing on disparate aspects of the problem. The nature of this project is to complete a thorough and rigorous investigation of global blockage, and to identify and characterise the principal exacerbating aspects of wind farm design that result in blockage. There remains a degree of uncertainty on the precise definition and quantification of wind farm blockage, this project will have to identify from literature or create such definitions. The investigation will be experimental in nature, taking place in the wind tunnels at Imperial College London, namely the 10ft x 5ft Low Speed National Wind Tunnel Facility. As alluded to previously, the energy lost to blockage is only a small percentage (around 2%) of the total energy yield of the wind farm. With the influence of blockage being so small, considerable care must be taken to ensure any results are distinguishable from measurement uncertainty. As the need to go carbon neutral increases and the necessity of wind energy increases, high wind yield locations such as the North Sea will become in increasing demand. With more and more farms being developed, global blockage is only going to play an increasingly less subtle role. The potential results of this investigation could have important bearing on the design of future wind energy projects. Characterisation of blockage may allow for it to mitigated and increase energy yields or if it cannot be mitigated, it will allow for a more accurate picture to be developed of the financial viability of a particular wind energy project.