Wind Turbine Aerodynamics

水平轴风力发电机的空气动力学仍有许多有待改进的课题。叶片单元理论（blade element theory， BET）是一种估算风力机性能的简单方法，普遍用于叶片优化，是许多控制算法和运行模型的基础，本文主要关注四个方面：***1。低叶尖速比（TSR）。该项目将发展目前关于有限叶片数下尾流动量和角动量的BET方程中出现的“非线性”项的工作，特别是在低TSR下。在此基础上，建立了低TSR条件下的尾迹扩展模型，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以及当前叶尖损失模型不准确的情况下的应用，例如扩压器增强风力涡轮机。* * * 2。坚固。BET将叶片元素视为翼型，相当于假设零固体度，定义为叶片元素弦与相邻叶片上叶片元素的周向距离的比率。一个具有不同叶片数量的风洞模型涡轮机将被用于进一步研究坚固性和低TSR效应。一项已经开始的关于翼型“叶栅”固体性的计算流体动力学研究将用于解释实验结果。低雷诺数（Re）。小型风力涡轮机在低Re下运行，并且在这些条件下经常受到低升阻比的影响。目前在UofC进行的用于确定低Re条件下翼型升力和阻力的风洞试验，正在扩展到包括在低Re条件下尚未研究的结冰影响。对两种结冰叶片（以及结冰机制）的同步CFD研究将用于与使用快速原型近似的通用结冰形状的实验进行比较。***4。叶片气动载荷不均匀。最近，作者首次从理论上证明了当叶片气动不均匀时，BET会产生额外的诱导速度。造成这种不平衡的原因有很多，比如风切变和（单个）俯仰角不相等。这些例子将用于扩展不等载荷理论，并追踪其在涡轮传动系统瞬态载荷方面的意义。关于结冰和不均匀叶片负荷及其对风力涡轮机动力学的影响的实用信息将与一家大型风力发电场所有者合作，提供给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.