Wind Turbine Aerodynamics

水平轴风力涡轮机的空气动力学仍然包含许多需要进行重要改进的主题。这项建议侧重于叶片元件理论(BET)背景下的四个领域，BET是一种评估风力涡轮机性能的简单方法，普遍用于叶片优化，是许多控制算法和运行模型的基础：*1.低叶尖速比(TSR)。该项目将发展目前在BET方程中出现的关于有限叶片数特别是低TSR时尾迹动量和角动量的“非线性”项的工作。同时，建立了低TSR下的扩展尾迹模型，并将其应用于精确确定叶片数量有限的叶尖损失的相关问题。这项工作将是DG项目的主要组成部分。主要合作者将是瓦列里·奥库洛夫教授(丹麦DTU风能系)。建议推广Wood和Okulov最近导出的叶尖损失的直接计算，以改进其在BET计算中的数值行为，并研究尾迹扩展的影响及其在当前叶尖损失模型不准确的情况下的应用，例如扩散器增强型风力涡轮机。*2.坚固。BET将叶片元件视为翼型，相当于假定为零实度，定义为叶片元件弦向距离与相邻叶片上的叶片元件的周向距离之比。不同叶片数的风洞模型涡轮机将被用来进一步研究坚固性和低TSR效应。已经开始的计算流体力学研究将被用来解释实验结果。*3.低雷诺数(Re)。小型风力涡轮机在低Re下运行，在这些条件下通常会受到低升阻比的影响。目前在加州大学进行的用于确定低Re下翼型升力和阻力的风洞试验正在扩展，以包括结冰的影响，这一影响在低Re下还没有研究过。同时对两种结冰叶片的CFD研究(以及结冰机理)将被用来与使用快速成型近似的通用结冰形状的实验进行比较。*4.气动载荷不相等的叶片。最近，这位学者首次从理论上证明了当叶片气动不相等时，BET内会产生附加的诱导速度。这种不平等可能有多种原因，例如风切变和(个别)俯仰角不相等。这些例子将被用来扩展不均匀载荷理论，并根据涡轮传动系统上的瞬时载荷来追踪它的意义。有关结冰和叶片负载不均匀及其对风力涡轮机动态的影响的实用信息将提供给与一个主要风力发电场所有者合作的关于涡轮机资产管理的新项目。

The aerodynamics of horizontal-axis wind turbines still contains many topics where important improvements are to be made. This proposal focuses on four areas in the context of blade element theory (BET), the simple method of estimating wind turbine performance that is universally used for blade optimization, and is the basis for many control algorithms and operational models:***1. low tip speed ratio (TSR). The project will develop current work on the "nonlinear" terms that arise in BET equations for momentum and angular momentum in the wake for finite blade numbers particularly at low TSR. In conjunction, a model of the expanding wake at low TSR will be developed and applied to the related problem of accurate determination of the tip loss which accounts for the finite number of blades. This work will the main component of the DG project. The main collaborator will be Professor Valery Okulov (Dept Wind Energy, DTU, Denmark). It is proposed to extend Wood and Okulov's recently derived direct calculation of tip loss to improve its numerical behaviour in BET calculations and to investigate the effects of wake expansion and the application to cases where current tip loss models are inaccurate, such as diffuser-augmented wind turbines. ***2. Solidity. BET treats the blade elements as airfoils which is equivalent to assuming zero solidity, defined as the ratio of the blade element chord to the circumferential distance to the blade elements on adjacent blades. A wind tunnel model turbine with varying numbers of blades will be used to further investigate solidity and low TSR effects. An already-started computational fluid dynamics study of solidity for "cascades" of airfoils will be be used to interpret the experimental results.***3. Low Reynolds number (Re). Small wind turbines operate at low Re and are often compromised by the low lift:drag ratio at these conditions. Current wind tunnel tests at the UofC to determine the lift and drag of airfoils at low Re, are being extended to include the effects of icing which has not been studied at low Re. Concurrent CFD studies of both iced blades (and the mechanism of icing) will be used to compare with the experiments which use rapid-prototyping approximations to generic icing shapes.***4. Blades with unequal aerodynamic loading. Recently, the proposer showed theoretically for the first time that additional induced velocities occur in BET when the blades are aerodynamically unequal. This inequality can have many causes, such as wind shear and unequal (individual) pitch angles. These examples will be used to extend the theory of unequal loading and to trace its significance in terms of transient loads on the turbine drivetrain. Practical information on icing and unequal blade loading and its consequences for wind turbine dynamics will feed into a new project on turbine asset management in conjunction with a major wind farm owner.