风力机叶片挥舞和摆振的位移时间序列的分形特性

为了研究风力机叶片挥舞和摆振的位移时间序列具有分形特征,基于数学形态学的分形维数计算方法,证明风力机叶片挥舞和摆振的位移时间序列具有标度不变性;通过分析长程相关性与自相似性的关系,由Hurst指数证实上述位移时间序列具有自相似性。理论分析和计算结果表明:挥舞和摆振的位移时间序列具有自相似特征,为采用分形理论研究风力机叶片动态特性奠定了数学基础,所揭示的时间序列整体与局部之间关系以及其自相似性,是基于挥舞和摆振位移时间序列数据进行风力机叶片故障诊断的技术支撑。     

潮流能水平轴水轮机叶片专用翼型族设计

针对潮流能水平轴水轮机的水动力学特性的特殊要求,采用直接数值优化方法进行潮流能水平轴水轮机叶片翼型优化设计,得到最大相对厚度介于12%～40%之间、适用于从叶片尖部到根部的7个不同厚度的OUC-TTXXX潮流能水平轴水轮机专用翼型,数值模拟和模型水槽试验结果表明所设计的OUC-TT-XXX潮流能水平轴水轮机翼型族具有良好的水动力学性能。     

线性波作用下水平轴潮流能水轮机水动力性能的数值模拟

文章以20 kW水平轴潮流能水轮机为例,分别选取正常工况和极限工况下的波浪参数,运用计算流体动力学软件Fluent对线性波作用下的水平轴潮流能水轮机的水动力性能进行了数值模拟。数值模拟结果表明:水平轴潮流能水轮机在波浪作用下会受到交变的海洋环境载荷的作用,在该环境载荷的作用下,水轮机的各项水动力性能参数发生周期性变化;正常工况下,水轮机水动力性能参数的波动幅度为3%左右,波浪对水轮机的影响不大;极限工况下,水轮机水动力性能参数的波动幅度为35%左右,波浪对水轮机的影响很大。波浪对水轮机的影响不容小觑,对此,工程上应尽量避开波浪影响区或采取适当的措施提高水平轴潮流能水轮机叶片和支撑结构的疲劳强度,以减小波浪对水平轴潮流能水轮机性能的影响和破坏。     

新型潮流能发电装置的水动力学特性模拟

为深入分析水平轴潮流能发电装置的水动力性能,文章建立了叶轮和导流罩模型,使用计算流体力学理论（CFD）和流体仿真软件FLUENT对水轮机叶轮与导流罩周围的流场分布进行模拟分析,并对3种叶片数和6种导流罩张角下的水轮机进行数值模拟,模拟结果表明：当叶片数为4,导流罩张角为25°时,水轮机输出功率与获能效率均达到了较为理想的效果。研究结果可为今后新型水平轴潮流能发电装置的结构设计与优化提供参考和依据。     

潮流能水轮机叶片在多安装角下的水动力研究

为精确控制潮流能水轮机的输出功率与载荷,得到叶片安装角控制规律,基于动量叶素理论、粘性CFD数值模拟以及模型试验的方法,对1 k W水轮机模型在不同安装角度下的水动力性能进行研究,计算水平轴潮流能水轮机叶片在不同安装角下的水动力性能与载荷。数值模拟与理论计算的结果表明:叶片安装角度的改变对水轮机的输出功率与载荷均有较明显影响,并呈现一定规律;通过模型实验验证了数值模拟方法的可靠性。     

多工况条件下变叶片数潮流能水轮机能量及流动特性研究

文章建立了潮流能水轮机水动力性能数值计算模型,通过实验验证了利用该模型预测水轮机尾流的准确性,并利用该模型研究了潮流能水轮机在不同叶片数和不同叶尖速比条件下的能量和流动特性。研究结果表明:该数值计算模型在预测尾流速度亏损和湍流强度方面具有较好的精度,尤其在远尾流区,数值计算结果与实验结果保持一致;当叶尖速比(TSR)为4.5左右时,3叶片和4叶片的潮流能水轮机具有相对较高的获能系数,此结果对于水平轴潮流能水轮机的设计具有一定的指导意义。     

单桩结构的潮流能水轮机尾流流场分析

为降低潮流能水轮机尾流效应对机组间距的影响,合理布置水轮机位置,通过数值模拟和水槽实验的方法对具有单桩支撑结构的潮流能水轮机尾流流场进行研究,在此基础上分析具有单桩支撑结构和不同安装高程对潮流能水轮机尾流流场的影响。结果显示:数值模拟与水槽试验总体上数值模拟与实验结果的趋势具有一致性;单桩结构对纵向近尾流场造成影响,会产生一个谷值突变;安装高程越高则导致沿转轮中心直线处的流速恢复越快。     

海浪条件下水平轴叶片式潮流能水轮机流动特性的数值模拟

为了研究自由海浪条件下的高潮汐流速对水平轴潮流能水轮机的动态特性影响，基于STAR-CCM+建立了海浪条件下潮流能水轮机水动力特性的数值模拟方法，得到了海浪对潮流能水轮机转动影响规律及转动过程中产生的尾流特征。结果表明，潮流能水轮机角加速度的幅度与频率受海浪影响，但波动幅度小于海浪波动幅度、变化频率高于海浪波动频率；水轮机转动产生的尾流会使下一个水轮机的周围流场更紊乱，对叶片转动的影响、水轮机轴负载和能量利用率等方面会产生影响；压力脉动变化趋势分析认为，尾流对水轮机疲劳损伤并无太大影响。     

水槽尺寸对水平轴潮流能转轮试验效率的影响

潮流能水轮机模型试验受试验条件的制约,其试验相似性距实际运行差距很大。利用CFD分析软件计算了不同水槽宽度和深度情况下水平轴潮流能转轮的能量转换效率,采用无限翼展与有限翼展原理探索了水槽尺寸对潮流能转轮性能的影响,并与相应的水槽模型试验结果进行了对比,合理解释了两种不同环境下产生差异的原因,为不同水槽尺寸下的叶片式水平轴转轮模型试验与原模型换算提供了参考依据。     

偏流角对潮流能水轮机水动力影响研究

基于三维CFD数值模拟方法对潮流能水平轴水轮机进行分析研究,并与试验结果比较,验证该方法的有效性。通过改变迎流式和背流式偏流角的大小,研究不同偏流角对水平轴水轮机水动力特性的影响规律。结果表明:偏流使水轮机效率及轴向载荷的平均值下降,偏流20°时,迎流式和背流式效率最大下降分别约为5%和6%,轴向载荷系数最大下降分别为5.5%和7.0%;使瞬时值波动幅值增加,偏流角越大,波动幅值越大。     

基于惯容的风力机结构控制装置作用位置研究

针对基于惯容的结构控制装置（IDVA）最优作用位置问题,建立基于拉格朗日方程的风力机动力学模型,给出装置参数优化方法。优化问题考虑IDVA系统安装在塔架不同位置对减振性能的影响,以及塔架位移与IDVA相对位移之间的相互影响。结果表明：IDVA系统安装在塔架的位置越高减振效果越好。不考虑IDVA行程时,IDVA系统可极大提升减振性能;考虑IDVA行程时,IDVA系统减振性能有所下降,在该优化问题条件下,塔顶位移与IDVA行程存在冲突,无法同时得到改善。     

Development of a hydraulic control mechanism for cyclic pitch marine current turbines

Tidal power generation by means of marine current farms is potentially a large renewable energy resource which could be harnessed in many coastal waters. Its availability is highly predictable in time, and the technology promises high energy conversion efficiency along with a relatively low impact on sea life due to its relatively small disturbance of natural tidal flows.A series of devices have so far been proposed and developed for the extraction and conversion of kinetic energy present in tidal flows into useful electrical power [1]. Designs include horizontal axis turbines, vertical axis turbines, and devices with oscillating lift surfaces. Up to date no technology has firmly established itself.This paper describes a novel hydraulic control mechanism designed for vertical-axis marine current turbines of the straight-bladed Darrieus type. It has been found to significantly improve turbine efficiency over conventional Darrieus turbines when operated at low blade tip-speed to tidal-flow-velocity ratios (TSR) and to give the turbine the ability to self-start reliably. The control mechanism enforces a cyclic pivoting motion on the turbine blades as they move around their circular flight-path. The movement of the pitch control is of sinusoidal shape and is continuously variable in amplitude. The blade actuation is powered by the turbine's own rotation and is implemented using a swash-plate mechanism in conjunction with a hydraulic circuit for every blade. For surface piercing turbines, this control mechanism may be remotely positioned in a dry nacelle above sea level. If the appropriate design is applied, this can offer access to the cyclic pitch control mechanism, gearbox and generator, even when the turbine is operational, promising lower maintenance and operating costs compared with submerged systems.     

Investigation of the performance of a staggered configuration of tidal turbines using CFD

This paper investigates the influence of wake interaction and blockage on the performance of individual turbines in a staggered configuration in a tidal stream farm using the CFD based Immersed Body Force turbine modelling method. The inflow condition to each turbine is unknown in advance making it difficult to apply the correct loading to individual devices. In such cases, it is necessary to establish an appropriate range of operating points by varying the loading or body forces in order to understand the influence of wake interaction and blockage on the performance of the individual devices. The performance of the downstream turbines was heavily affected by the wake interaction from the upstream turbines, though there were accelerated regions within the farm which could be potentially used to increase the overall power extraction from the farm. Laterally closely packed turbines can improve the performance of those turbines due to the blockage effect, but this could also affect the performance of downstream turbines. Thus balancing both the effect of blockage and wake interaction continues to be a huge challenge for optimising the performance of devices in a tidal stream farm.     

Numerical analysis of the characteristics of vertical axis tidal current turbines

Tidal current is considered to be one of the promising alternative green energy resources. Tidal current turbines are devices used for harnessing tidal current energy. The development of a standard for tidal current turbine design is a very important step in the commercialization of tidal current energy as the tidal current industry is growing rapidly, but no standard for tidal current turbines has been developed yet. In this paper, we present our recent efforts in the numerical simulation of the characteristics (e.g., power output, torque fluctuation, induced velocity, and acoustic emission) of tidal current turbines related to the development of the standard. The relationship between the characteristics and the parameters of an example turbine are extensively discussed and quantified. The findings of this paper are expected to be helpful in developing the standards for tidal current turbines in the near future.     

Numerical simulation of the loading characteristics of straight and helical-bladed vertical axis tidal turbines

The stress and deflection of straight and helical-bladed vertical axis turbines was investigated using hydrodynamic and structural analysis models. Using Double Multiple Streamtube (DMS) and Computational Fluid Dynamics (CFD) models, the hydrodynamic forces and pressures on the turbines were modelled for three rotational rates from startup to over speed conditions. The results from these hydrodynamic models were then used to determine stress and total deflection levels using beam theory and Finite Element Analysis (FEA) methods. Maximum stress and deflection levels were found when the blades were in the furthest upstream region, with the highest stresses found at the blade-strut joints for the turbines studied. The helical turbine exhibited on average 13% lower maximum stress levels than the straight-bladed turbine, due to the helical distribution of the blades around the rotational axis. All simulation models offered similar accuracy when predicting maximum blade stress and deflection levels; however for detailed analysis of the blade-strut joints the more computationally demanding CFD-FEA models were required. Straight-bladed, rather than helical turbines, are suggested to be more suited for tidal installations, as for the same turbine frontal area they produce higher power output with only 13% greater structural stress loading.     

A computational hydrodynamics method for horizontal axis turbine – Panel method modeling migration from propulsion to turbine energy

A computational hydrodynamics method was formulated and implemented for horizontal axis tidal turbines. This paper presents a comparative analysis between screw propellers and horizontal axis turbines, in terms of geometry and motion parameters, inflow velocity analysis and the implementation methodologies. Comparison and analysis are given for a marine propeller model and a horizontal axis turbine model that have experimental measurements available in literature. Analysis and comparison are presented in terms of thrust coefficients, shaft torque/power coefficients, blade surface pressure distributions, and downstream velocity profiles. The effect of number of blades from 2 to 5, of a tidal turbine on hydrodynamic efficiency is also obtained and presented. The key implementation techniques and methodologies are provided in detail for the propeller based panel method tool to migrate as a prediction tool for tidal turbine. While the method has been proven to be accurate and robust for many propellers tested in the past, this numerical tool could be validated further for turbines. To further refine and validate the panel method for various turbines, it requires substantial additional experimental measurements. These measurements include downstream velocity profile by using LDV and/or SPIV, which are essential for numerical wake vortices descritization.     

Numerical investigations of the effects of different arrays on power extractions of horizontal axis tidal current turbines

As the tidal current industry grows, power extraction from tidal sites has received widespread attention. In this paper, a blade element actuator disk model that is coupled with the blade element method and a three-dimensional Navier–Stokes code is developed to analyse the relationship between power extraction and the layout of turbine arrays. First, a numerical model is constructed to simulate an isolated turbine and the model is validated using experimental data. Then, using this validated model, the power extraction of horizontal axis tidal current turbines using different tidal turbine arrays and rotation directions is predicted. The results of this study demonstrate that staggered grid array turbines can absorb more power from tidal flows than can rectilinear grid array turbines and that staggered grid array turbines are less affected by the rotation of upstream turbines. In addition, for staggered gird arrays, the relationships between power coefficients, lateral distance and longitudinal distance are discussed. The appropriate lateral distance is approximately 2.5 turbine diameters, whereas for the longitudinal distance, the largest value possible should be used. The relative power coefficient can achieve 3.74 when the longitudinal distance is 6 times the turbine diameter. To further increase the power extraction, this study suggests an improved staggered grid array layout. The relative power coefficient of the improved four-row turbine arrays is approximately 3–4% higher than that of the original arrays and will increase as the distance between the second-row and third-row increases. Considering only the first two rows of turbines, the total power extraction can be 11% higher than for an equivalent number of isolated turbines.     

柱状漂浮式风力机结构振动控制

针对柱状漂浮式风力机的结构振动控制展开研究。首先为进行调谐质量阻尼器(TMD)参数的优化,对风力机模型进行简化,并对简化模型中的未知参数进行估计;随后,基于简化模型分别使用公式法和遗传算法对TMD参数进行优化,并通过比较塔顶前后位移的标准偏差确定最终的优化方法;最后,为评估TMD对风力机振动控制的影响,构建风力机的联合仿真模型,并在3种典型工况下进行仿真分析。仿真结果表明,所设计的TMD可以很好地降低漂浮式风力机的载荷以及位移,有效抑制塔顶振动加速度与系泊缆绳有效张力,同时可有效降低额定风速以上时电功率输出的标准偏差,使电功率输出更加稳定。     

On applicability of reciprocating flow turbines developed for wave power to tidal power conversion

Tidal power generation with reciprocating turbines in a simple system is investigated on a performance simulation in order to enlarge the capability of practical use of tidal power with extra-low head and time-varying energy density characteristics. Four reciprocating turbines, which are two types of impulse and a Wells developed for wave power conversion systems, and a cross-flow type of Darrieus for extra-low head hydropower are focused for utilizing extra-low head tidal power. Their turbine characteristics in a unidirectional steady flow obtained by physical test models are compared in non dimensional forms and power plant performance with the turbines are numerically simulated on equivalently scaled turbines based on the low of similitude on turbine performance with the non dimensional characteristics under one of the simplest controls in combination with suitable reservoir ponds area. The output of the power plant depends on tidal difference and a pond inundation area. The results are summarized and discussed on the averaged electric output of the power plant and the optimum scale of pond inundation area.     

Flume tank characterization of marine current turbine blade behaviour under current and wave loading

The long term reliability of tidal turbines is critical if these structures are to be cost-effective. Optimized design requires a combination of material durability models and structural analyses which must be based on realistic loading conditions.This paper presents results from a series of flume tank measurements on strain gauged scaled turbine blades, aimed at studying these conditions. A detailed series of tests on a 3-blade horizontal axis turbine with 400 mm long blades is presented. The influence of both current and wave-current interactions on measured strains is studied. These tests show that wave-current interactions can cause large additional loading amplitudes compared to currents alone, which must be considered in the fatigue analysis of these systems.