Wind Turbine Aerodynamics

水平轴风力发电机的空气动力学仍然包含许多重要的改进课题。本提案侧重于叶素理论（BET）背景下的四个领域，叶素理论是估算风力涡轮机性能的简单方法，普遍用于叶片优化，并且是许多控制算法和操作模型的基础： 1.低叶尖速比（TSR）。该项目将开发当前关于“非线性”项的工作，这些项出现在BET方程中，用于有限叶片数（特别是在低总叶面积比时）的尾流动量和角动量。同时，将开发一个低TSR时的扩展尾流模型，并将其应用于精确确定叶尖损失的相关问题，该问题考虑到有限数量的叶片。这项工作将是DG项目的主要组成部分。主要合作者将是Valery Okulov教授（丹麦DTU风能系）。建议扩展Wood和Okulov最近导出的叶尖损失直接计算，以改善其在BET计算中的数值行为，并研究尾流膨胀的影响以及当前叶尖损失模型不准确的情况下的应用，如扩压器风力涡轮机。 2.坚固。BET将叶片元件视为翼型，这相当于假设零实度，实度定义为叶片元件弦与相邻叶片上叶片元件的周向距离之比。将使用具有不同叶片数量的风洞模型涡轮机进一步研究坚固性和低TSR效应。一个已经开始的计算流体动力学研究的坚实性的“叶栅”的翼型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，并且在这些条件下通常受到低升阻比的影响。目前在UofC进行的确定低雷诺数下翼型升力和阻力的风洞试验正在扩展，以包括在低雷诺数下尚未研究的结冰影响。将使用两种结冰叶片（和结冰机理）的并行计算流体动力学研究，与使用快速原型近似法对一般结冰形状进行的实验进行比较。 4.具有不等气动载荷的叶片。 最近，提议者首次从理论上证明，当叶片在空气动力学上不相等时，BET中会出现额外的诱导速度。这种不平等可能有许多原因，如风切变和不平等的（个人）桨距角。这些示例将用于扩展不等载荷理论，并跟踪其在涡轮机传动系瞬态载荷方面的意义。 有关结冰和不均匀叶片载荷及其对风力涡轮机动力学影响的实用信息将与主要风电场所有者一起提供给一个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.