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Massively parallel time- and frequency-domain Navier-Stokes Computational Fluid Dynamics analysis of wind turbine and oscillating wing unsteady flows

机译：大规模并行时域和频域的Navier-Stokes计算流体动力学分析，风力涡轮机和摆动翼非定常流动

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摘要

Increasing interest in renewable energy sources for electricity production complying with stricter environmental policies has greatly contributed to further optimisation of existing devices and the development of novel renewable energy generation systems. The research and development of these advanced systems is tightly bound to the use of reliable design methods, which enable accurate and efficient design. Reynolds-averaged Navier-Stokes Computational Fluid Dynamics is one of the design methods that may be used to accurately analyse complex flows past current and forthcoming renewable energy fluid machinery such as wind turbines and oscillating wings for marine power generation. The use of this simulation technology offers a deeper insight into the complex flow physics of renewable energy machines than the lower-fidelity methods widely used in industry. The complex flows past these devices, which are characterised by highly unsteady and, often, predominantly periodic behaviour, can significantly affect power production and structural loads. Therefore, such flows need to be accurately predicted.ududThe research work presented in this thesis deals with the development of a novel, accurate, scalable, massively parallel CFD research code COSA for general fluid-based renewable energy applications. The research work also demonstrates the capabilities of newly developed solvers of COSA by investigating complex three-dimensional unsteady periodic flows past oscillating wings and horizontal-axis wind turbines.ududOscillating wings for the extraction of energy from an oncoming water or air stream, feature highly unsteady hydrodynamics. The flow past oscillating wings may feature dynamic stall and leading edge vortex shedding, and is significantly three-dimensional due to finite-wing effects. Detailed understanding of these phenomena is essential for maximising the power generation efficiency. Most of the knowledge on oscillating wing hydrodynamics is based on two-dimensional low-Reynolds number computational fluid dynamics studies and experimental testing. However, real installations are expected to feature Reynolds numbers of the order of 1 million and strong finite-wing-induced losses. This research investigates the impact of finite wing effects on the hydrodynamics of a realistic aspect ratio 10 oscillating wing device in a stream with Reynolds number of 1.5 million, for two high-energy extraction operating regimes. The benefits of using endplates in order to reduce finite-wing-induced losses are also analyzed. Three-dimensional time-accurate Reynolds-averaged Navier-Stokes simulations using Menter's shear stress transport turbulence model and a 30-million-cell grid are performed. Detailed comparative hydrodynamic analyses of the finite and infinite wings highlight that the power generation efficiency of the finite wing with sharp tips for the considered high energy-extraction regimes decreases by up to 20 %, whereas the maximum power drop is 15 % at most when using the endplates.ududHorizontal-axis wind turbines may experience strong unsteady periodic flow regimes, such as those associated with the yawed wind condition. Reynolds-averaged Navier-Stokes CFD has been demonstrated to predict horizontal-axis wind turbine unsteady flows with accuracy suitable for reliable turbine design. The major drawback of conventional Reynolds-averaged Navier-Stokes CFD is its high computational cost. A time-step-independent time-domain simulation of horizontal-axis wind turbine periodic flows requires long runtimes, as several rotor revolutions have to be simulated before the periodic state is achieved. Runtimes can be significantly reduced by using the frequency-domain harmonic balance method for solving the unsteady Reynolds-averaged Navier-Stokes equations. This research has demonstrated that this promising technology can be efficiently used for the analyses of complex three-dimensional horizontal-axis wind turbine periodic flows, and has a vast potential for rapid wind turbine design. The three-dimensional simulations of the periodic flow past the blade of the NREL 5-MW baseline horizontal-axis wind turbine in yawed wind have been selected for the demonstration of the effectiveness of the developed technology. The comparative assessment is based on thorough parametric time-domain and harmonic balance analyses. Presented results highlight that horizontal-axis wind turbine periodic flows can be computed by the harmonic balance solver about fifty times more rapidly than by the conventional time-domain analysis, with accuracy comparable to that of the time-domain solver.
机译：遵循更严格的环境政策，对用于电力生产的可再生能源的兴趣日益增加，极大地促进了现有设备的进一步优化和新型可再生能源发电系统的开发。这些先进系统的研究与开发紧密地依赖于使用可靠的设计方法，从而可以进行准确而有效的设计。雷诺平均的Navier-Stokes计算流体动力学是一种设计方法，可用于准确分析经过当前和即将到来的可再生能源流体机械（例如风力涡轮机和用于海上发电的摆动翼）的复杂流动。与工业上广泛使用的低保真度方法相比，使用这种模拟技术可以更深入地了解可再生能源机器的复杂流场。经过这些设备的复杂流量具有高度不稳定的特点，并且通常主要表现为周期性行为，会严重影响电力生产和结构负荷。因此，需要对这种流量进行准确的预测。 ud ud本论文中的研究工作涉及为常规的基于流体的可再生能源应用开发新颖，准确，可扩展，大规模并行CFD研究代码COSA。该研究工作还通过研究经过摆动翼和水平轴风力涡轮机的复杂三维非定常周期性流动，证明了新开发的COSA求解器的功能。摆动翼用于从迎面而来的水或空气流中提取能量，具有高度不稳定的流体动力学特性。经过摆动的机翼的气流可能具有动态失速和前缘涡旋脱落的特征，并且由于有限的机翼效应，气流明显为三维。对这些现象的详细了解对于最大化发电效率至关重要。关于摆动翼流体动力学的大多数知识是基于二维低雷诺数计算流体动力学研究和实验测试的。但是，实际的安装预计将具有雷诺数1百万的数量级以及有限的机翼引起的强烈损失。这项研究调查了雷诺数为150万的流中两种高能量提取操作方案中有限机翼效应对实际长宽比10振荡机翼装置的流体动力学的影响。还分析了使用端板以减少有限翼引起的损失的好处。使用Menter的切应力传递湍流模型和3000万个单元的网格，进行了三维时间精确的雷诺平均Navier-Stokes模拟。对有限翼和无限翼的详细比较流体力学分析表明，对于考虑到的高能量抽取状态，具有尖锐尖端的有限翼的发电效率最多降低20％，而使用时最大功率下降最多为15％ ud ud水平轴风力涡轮机可能会遇到强烈的不稳定的周期性流动状态，例如与偏航风况相关的状态。雷诺平均的Navier-Stokes CFD已被证明可以预测水平轴风力发电机的非恒定流量，其准确度适合可靠的风力发电机设计。常规雷诺平均Navier-Stokes CFD的主要缺点是计算成本高。水平轴风力涡轮机周期性流动的与时间步无关的时域仿真需要较长的运行时间，因为在达到周期性状态之前必须先模拟几次转子旋转。通过使用频域谐波平衡方法求解不稳定的雷诺平均Navier-Stokes方程，可以大大减少运行时间。这项研究表明，这项有前途的技术可以有效地用于分析复杂的三维水平轴风力涡轮机的周期性流动，并具有快速风力涡轮机设计的巨大潜力。选择了偏航中经过NREL 5兆瓦基线水平轴风力涡轮机叶片的周期性流动的三维模拟，以证明所开发技术的有效性。比较评估基于彻底的参数时域和谐波平衡分析。提出的结果表明，谐波平衡求解器可以比常规时域分析更快地计算出水平轴风力发电机的周期性流量，其精度可与时域求解器相媲美。

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    Drofelnik Jernej;

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