Research on Pitch Control Strategies of Horizontal Axis Tidal Current Turbine

Based on blade element momentum theory and generator characteristic test,a dynamic simulation model of 150 kW horizontal-axis tidal current turbine was established.The matching of the dynamic characteristics between the turbine and generator under various current velocities is studied,and the influence of the pitch angle on the matching is analyzed.For the problem of maximum power output in case of low current speed and limiting power in high current speed,the relation between optimal pitch angle and output power is analyzed.On the basis of dynamic characteristic analysis,the variable pitch control strategy is developed.The performance of the turbine under various tidal conditions is simulated.The research results show that the designed controller enables the turbine to operate efficiently under the condition of low current speed,and achieve the goal of limited power at high current speed.

Numerical Investigation of Flow Motion and Performance of A Horizontal Axis Tidal Turbine Subjected to A Steady Current

Horizontal axis tidal turbines have attracted more and more attentions nowadays, because of their convenience and low expense in construction and high efficiency in extracting tidal energy. The present study numerically investigates the flow motion and performance of a horizontal axis tidal turbine with a supporting vertical cylinder under steady current. In the numerical model, the continuous equation and incompressible Reynolds-averaged Navier-Stokes equations are solved, and the volume of fluid method is employed to track free surface motion. The RNG k-ε model is adopted to calculate turbulence transport while the fractional area/volume obstacle representation method is used to describe turbine characteristics and movement. The effects of installation elevation of tidal turbine and inlet velocity on the water elevation, and current velocity, rotating speed and resultant force on turbine are discussed. Based on the comparison of the numerical results, a better understanding of flow structure around horizontal axis tidal turbine and turbine performance is achieved.

Design and Test of 1/5th Scale Horizontal Axis Tidal Current Turbine

Tidal current energy is prominent and renewable. Great progress has been made in the exploitation technology of tidal current energy all over the world in recent years, and the large scale device has become the trend of tidal current turbine （TCT） for its economies. Instead of the similarity to the wind turbine, the tidal turbine has the characteristics of high hydrodynamic efficiency, big thrust, reliable sealing system, tight power transmission structure, etc. In this paper, a l/5th scale horizontal axis tidal current turbine has been designed, manufactured and tested before the full scale device design. Firstly, the three-blade horizontal axis rotor was designed based on traditional blade element momentum theory and its hydrodynamic performance was predicted in numerical model. Then the power train system and stand-alone electrical control unit of tidal current turbine, whose performances were accessed through the bench test carried out in workshop, were designed and presented. Finally, offshore tests were carried out and the power performance of the rotor was obtained and compared with the published literatures, and the results showed that the power coefficient was satisfactory, which agrees with the theoretical predictions.

Numerical Study of A Generic Tidal Turbine Using BEM Optimization Methods

Three blade-geometry optimization models derived along with assumptions from the blade element momentum(BEM)approach are studied by using a steady BEM code to improve a small horizontal-axis rotor of three blades that has been previously used in experiments.The base rotor blade has linear-radially varying chord length and pitch angle,while the other three models noted as Burton,Implicit and Hansen due to their references and characteristics yield blades of non-linearly varying chord length and pitch angle.The aim is to compare these rapid models and study how assumptions embedded in them affect performance and induction factors.It is found that the model that has the least assumptions(Hansen)and which considers the blade-profile drag in its optimization procedure yields the highest power coefficient,C_(P),at the optimal tip speed ratio(TSR),about 7%higher than the base one and also higher C_(P) at high TSR.It produces an axial induction factor distribution along the blade that is closest to the 1 D optimal value of 1/3.All optimized tangential induction-factor distributions along the blade closely vary as inverse to the square of the radial distance,while being mildly higher than the base distribution.It shows that sufficient swirl is necessary to increase power but at a level causing not too much energy loss in unnecessary swirl of the wake.At high TSR,all optimized rotors adversely produce higher thrust than the base one,but the one with most embedded assumptions(Burton)produces the highest thrust.Details of all three optimization models are given along with the distributions of the power,thrust,blade hydrodynamic efficiency and induction factors.

Optimization of Blade Motion of Vertical Axis Turbine

In this paper,a method is proposed to improve the energy efficiency of the vertical axis turbine.First of all,a single disk multiple stream-tube model is used to calculate individual fitness.Genetic algorithm is adopted to optimize blade pitch motion of vertical axis turbine with the maximum energy efficiency being selected as the optimization objective.Then,a particular data processing method is proposed,fitting the result data into a cosine-like curve.After that,a general formula calculating the blade motion is developed.Finally,CFD simulation is used to validate the blade pitch motion formula.The results show that the turbine＇s energy efficiency becomes higher after the optimization of blade pitch motion;compared with the fixed pitch turbine,the efficiency of variable-pitch turbine is significantly improved by the active blade pitch control;the energy efficiency declines gradually with the growth of speed ratio;besides,compactness has lager effect on the blade motion while the number of blades has little effect on it.

Experimental study of hydrodynamic performance of full-scale horizontal axis tidal current turbine

In this paper, experiments of both the model turbine （1 kW） and the full scale （10 kW） turbine are carried out in a towing tank and a basin, respectively, and the test of the full scale turbine on the sea is conducted. By comparison between the model turbine （D = 0.7 m） and the full scale turbine （D = 2.0 m）, it is shown that the maximum power coefficient increases with the increase of the diameter of the turbine. The test results on the sea are used to study the hydrodynamic performances of the horizontal axis turbine, and provide a basis for the design. Experimental results can validate the accuracy of the numerical simulation results.

Numerical study of power production from tidal energy in the Khuran Channel and its feedback on background hydrodynamics

This study focuses on the development of a farm of tidal turbines in the Khuran Channel.The important factors include the location of turbines and their hydrodynamic effects on the environment.A three-dimensional circulation model for the Persian Gulf is employed for the comprehensive evaluation of the tidal energy potential throughout the study area.The model is validated by using in situ observations of water level and current data.The appropriate potential points for extracting the tidal energy were identified in the Persian Gulf using the model results.The Khuran Channel,located in the north of Qeshm Island,was found to be the best place to extract tidal energy inside the Persian Gulf.By adding the term of momentum losses to the governing equations,the feedback of extracting energy on the hydrodynamic around Qeshm Island was studied.The simulation results show that the average daily power production of a tidal farm with 99 turbines for one month is approximately 1.3 MW.This tidal farm also has a significant impact on the water level inside the Khuran Channel,especially near the tidal farm where these fluctuations exceed 4 cm.The change in the current speed caused by wake reaches 0.4 m/s.Wake effects were active up to 7 km downstream of the turbines.The current velocity was also estimated to be 1.6 m/s and 2.1 m/s during the spring and ebb tides within the channel,respectively.

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。

水平轴潮流能水轮机实验方法发展现状

潮流能可预测性强、能量密度大,具有广阔的开发前景。水平轴潮流能水轮机是发电效率最高的潮流能装置,世界各国对水平轴潮流能水轮机进行了大量实验研究。本文阐述了国内外水平轴潮流能水轮机的实验方法,包括实验设施、实验模型、实验平台和测量方法;并从均匀流和复杂环境两个方面对水平轴水轮机的模型实验现状进行总结和评价;分析目前水平轴潮流水轮机模型实验中存在的不足,并对未来的水轮机模型实验提出了一些建议,这对潮流能的开发具有重要意义。

浮式水平轴潮流能水轮机横摇艏摇耦合运动水动力性能分析

浮式潮流能装置的水轮机会随着与之刚性连接的载体在波浪作用下发生六自由度运动。为了研究横摇和艏摇耦合运动对其影响,采用滑移网格技术实现无界均匀流环境下水轮机在不同频率下横摇艏摇同频同幅耦合运动的非定常模拟,在网格无关性验证的基础上,将数值模拟的结果与水槽试验中扭矩传感器测量值对比来验证数值模拟结果的准确性。结果表明:水轮机的能量利用系数和轴向载荷系数平均值相比于无摇时分别约减小0.035和增大0.02,瞬时值出现周期波动且波动规律与仅发生艏摇运动时基本一致,当耦合运动频率为2 rad/s时,能量利用系数和轴向载荷系数瞬时值的变化幅度分别约为8.6%和5.9%;叶轮正面和背面压力出现不均匀分布且在平衡位置处最为严重,尾流场低速区和高涡量区域出现明显摆动,近尾流区的速度恢复加快但远尾流区域速度恢复变慢。

潮流能水平轴水轮机流场分析

用OpenFOAM开源软件对水平轴水轮机进行数值模拟,以推力T作为体积力附加源项均匀加载到制动盘模型(AD),进行求解计算。在尖端速度比(TSR)为5.5的条件下,对自由区、单台水轮机、水轮机阵列3种情况下的流场进行分析。结果显示:在来流上游时,三者流速曲线吻合,流速增长趋势一致。水流在AD前端时,AD会对其有阻力作用,导致流速大幅下降。在尾流处,在水轮机阵列上游中,并列两侧水轮机尾流与下游水轮机流场发生动能交换,使其尾流恢复速度大于单台水轮机尾流速度。然而,无论是单台水轮机还是水轮机阵列,它们轴线方向上的中部尾流恢复严重不足,这是由于尾流的干涉使得下游水轮机的来流速度不断减小,其可吸收转化的能量也减少,速度随之减小,尾流也无法恢复。

剪切流下潮流能水平轴水轮机的水动力分析

为研究剪切流下潮流能水平轴水轮机的水动力问题,本文采用叶素动量理论与动态入流模型相结合的方法,考虑相对入流速度的时域变化,计算了不同剪切率下水轮机的各水动力系数,探究了剪切率对潮流能水平轴水轮机的水动力载荷特性的影响规律。经验证,数值模型与CFD模拟结果吻合良好。结果表明:一定范围内,同一速比下,剪切率对时均轴向力系数的影响不明显,对时均功率系数的影响大约以最优速比为分界,高速比时剪切率越大,功率系数越大,低速比时关系不明显;水动力系数的波动周期与叶轮旋转周期存在倍数关系;水动力系数的幅值与剪切率呈近似线性关系。本文可为剪切流下潮流能水平轴水轮机的载荷分析、设计优化提供有效的预报。

池壁效应对水平轴潮流涡轮水动力性能影响分析

为了分析池壁效应对水平轴潮流涡轮水动力性能的影响,本文采用数值仿真与模型试验的方式测试直径300 mm潮流涡轮的水动力性能,并对数值仿真方法进行验证;采用Bahaj修正方法与数值仿真方法对不同流域、流速下涡轮的能量转换效率以及阻力系数进行对比,进一步分析池壁效应对涡轮桨盘处以及尾流区域流场的影响。研究结果表明:池壁效应对水平轴潮流涡轮的水动力性能影响明显,其对能量转换效率影响伴随尖速比的增加逐渐增大;池壁效应对潮流涡轮桨盘处的轴向流速以及流场分布影响较小,但对潮流涡轮尾流区轴向速度恢复影响明显。研究结果可为水平轴潮流涡轮水动力性能的数值仿真研究与试验提供相关数据以及参考。

潮流能水平轴水轮机湍流模型研究初探

借助计算流体力学(CFD)方法研究潮流能水平轴水轮机水动力学性能,选择合适的湍流模型至关重要。为此,本文采用计算流体力学软件Fluent,将Spalart-Allmaras湍流模型、标准k-ε湍流模型、RNGk-ε湍流模型、标准k-ω湍流模型和SSTk-ω湍流模型分别应用到水平轴水轮机数值模拟当中。对数值模拟结果进行分析比较,并与模型试验数据进行对比,得出应用SSTk-ω湍流模型可以更好的模拟潮流能水平轴水轮机的水动力学性能。

水平轴潮流能发电机组独立变桨距系统

针对水平轴潮流能发电机组轮毂空间小、变桨角度大、变桨力矩大等特点,设计一种新型的基于电液比例控制的齿轮齿条传动方案的独立变桨距系统.该系统机械结构紧凑,占用空间小,各个桨叶变桨执行机构相互独立.在分析变桨距载荷的基础上,建立系统的数学模型,并在AMESim软件中对系统进行了仿真研究.仿真结果表明:该系统顺桨变桨180°只需1.1s,逆桨变桨180°只需3.4s,响应速度快,稳定性好,并且可以实现独立变桨,满足了水平轴潮流能发电机组的变桨要求.

两种湍流模型在潮流能水轮机数值模拟中的适用性研究

在对特定湍流条件下的水平轴潮流能水轮机进行数值模拟时,不同的湍流模型对于计算结果具有一定的影响。为选择合适的湍流模型对所设计水轮机的三维流场进行描述,将采用常用的两方程模型(SSTk-ω与Realizable k-ε)进行数值模拟,得到不同工况下水轮机的性能参数以及水轮机后1.5D处流场的流速、湍流强度分布情况,并进行模型水槽试验,试验值与采用两种湍流模型进行数值模拟得到的仿真值对比表明:在低尖速比工况下,采用SSTk-ω进行数值模拟得到的仿真值比Realizable k-ε更接近试验值,在较高尖速比时,采用Realizable k-ε进行模拟得到的数值更接近试验值;采用两种湍流模型进行数值模拟得到的速度分布具有相似性,但对于湍流强度的预测,SSTk-ω更具有优势。考虑此水轮机的实际工况,选择SSTk-ω湍流模型进行描述更加合理。

垂直轴潮流能水轮机叶片偏角优化

为提高垂直轴潮流能水轮机的能量利用率,建立了叶片偏角变化规律的数学优化模型.该模型是将一个运动周期内的叶片偏角相对位置角的函数关系表示成Hicks-Henne函数族的线性和,并将此函数关系带入叶轮的水动力计算中.然后以函数族的系数为设计参数,以水轮机能量利用率为目标函数,采用旋转方向法进行优化计算,以此得到最合理的叶片偏角变化规律.计算叶轮的流体动力性能时采用双盘面多流管法.最后,采用本文方法对摆线式水轮机进行了优化.算例结果显示,采用优化偏角的水轮机与原摆线式水轮机相比,能量利用率有较大提高,并且启动性能更好.

水平轴潮流能水轮机耦合运动水动力分析

漂浮式潮流能装置载体的波浪运动响应使水平轴水轮机的水动力特性发生变化,采用滑移网格技术对无界均匀来流中水轮机发生横摇和纵摇耦合运动时的三维水动力特性进行研究.结果表明:水轮机轴向载荷和能量利用率瞬时值产生波动,且横摇和纵摇耦合运动时轴向载荷及能量利用率的计算结果与只发生纵摇运动的计算结果基本相同;横摇和纵摇耦合运动时横摇力矩计算值的波动幅值比只发生横摇运动时的大;横摇和纵摇耦合运动时纵摇力矩的计算值与只发生纵摇运动时的计算值存在差异,横摇频率越大,差异越明显.研究结果可为漂浮式载体的运动响应研究、水轮机的结构设计及电能控制等提供相关数据.

潮流能水平轴水轮机叶片优化研究

叶片对潮流能水轮机的性能有很大的影响,因此对叶片进行优化研究对于提高潮流能水轮机的效率的重大意义。本文对50kW潮流能水平轴水轮机进行了叶片设计,针对水轮机具体的运行环境,以提高水轮机获能为目标,应用遗传算法对叶片弦长和扭角进行了优化设计。通过对比实际工况下水轮机的获能特性得知,优化的叶片获能系数和获能功率较原叶片有所提高,从而证明应用遗传算法进行叶片优化的可行性,为水轮机叶片优化提供了新的方法。

潮流能水平轴水轮机空化数值模拟

以50 k W潮流能水平轴水轮机为例进行叶片设计,采用计算流体力学软件Fluent分别模拟全湿流模型和空化流模型的水轮机水动力学性能,数值模拟结果表明水轮机运行过程中存在空化现象,空化首先发生在背流面叶片尖端,由叶片尖端向叶片中部发展,空化的发生可降低水轮机的功率系数和扭矩系数,增大水轮机的轴向力系数,工程上应采取相应的措施。