竖轴潮流能水轮机群数值模拟研究

为了实现竖轴潮流能水轮机群的优化布置,基于CFD方法分别对单排和双排水轮机群进行数值模拟。对于单排水轮机群排布,水轮机只有相互十分靠近时其输出效率才会得到显著提升,而相邻水轮机相对旋转方向对机群的效率无影响。对于双排水轮机群排布,下游水轮机会使上游水轮机的尾流变窄、流速加快,但对上游水轮机的效率无影响。合理选择上游水轮机的间距可提高下游水轮机的效率,优化的双排水轮机群排布方案大幅提升了整个机群的效率。     

竖轴潮流能水轮机组排列规律试验研究

针对竖轴潮流能水轮机阵列的水动力性能,在拖曳水池中开展模型试验研究。研究竖轴潮流能水轮机阵列整体水动力性能模型试验技术,讨论给定转速、流速的情况下双水轮机阵的能效指数。通过改变两个水轮机模型的相对位置,分析水轮机轴间距、轴心连线与来流的偏角对能效指数的影响规律。     

竖轴潮流能水轮机叶片安装位置研究

将竖轴潮流能水轮机简化为二维形式,以二维机翼非定常运动数值分析方法为基础,构建多机翼非定常运动的边界元法模型,并在此基础上开发竖轴潮流能水轮机结构受力数值预报方法。利用该方法研究竖轴潮流能水轮机叶片安装位置对水轮机叶片、水轮机转子受力的影响规律。研究表明:安装位置靠近叶片翼型可提升水轮机的获能效率,安装位置靠近翼型中部可使叶片、转子的受力减小。     

竖轴水轮机空化对捕获功率的影响研究

竖轴潮流水轮机是目前被广泛研究的潮流能的转换装置。利用CFD软件FLUENT的滑移网格模型、多相流模型和用户自定义函数UDF,通过求解动量方程、连续性方程以及气泡输运方程,分别在忽略空化的全湿流和考虑空化的空化流情况下对竖轴潮流水轮机进行了非定常数值模拟。结果表明,两种数值模型下的水轮机附近的流场在水轮机的上游面差别很大,空化不仅使水轮机叶片周围产生气泡,而且严重扰乱了水轮机叶片周围的流场,从而导致水轮机水动力性能的改变。空化的存在使潮流水轮机叶片对主轴的作用力减小,使水轮机的能量利用率Cp降低,当尖速比λ=2.75时,Cp值最大,为0.23,比忽略空化时降低了25%。     

横向布置单桩潮流能水轮机的数值模拟研究

文章以单桩潮流能水轮机为研究对象,通过数值计算的方法对横向布置下两台单桩潮流能水轮机的尾流场及机组性能进行研究。通过对比不同横向间距下单桩潮流能水轮机的尾流场,获得了横向间距对潮流能水轮机尾流场的影响规律。数值计算结果表明:单桩结构会改变水轮机的纵向尾流场,但对横向尾流场的影响较小;随着横向间距的改变,机组的功率系数和推力系数的变化幅值不超过0.01;横向间距对机组的横向尾流场也造成了影响,导致各个机组的尾流中心偏向两个机组的中间位置,且随着横向间距的增大,机组u/U0低于0.9的范围随之增大,幅值可达0.26D。     

导流涵道对垂直轴水轮机性能影响的研究

垂直轴水轮机作为重要的潮流能捕获装置,相比于水平轴水轮机,它具有结构简单、适应任意水流等优点,但获能效率较低。为了增大垂直轴水轮机的获能效率,文章提出了一种导流涵道装置。采用CFD方法研究了其增速性能,并探究了水轮机在导流涵道下的输出扭矩特性,最后讨论了水轮机与导流涵道之间的间距对获能效率和转矩的影响。研究表明:导流涵道在一定程度上增大了来流的速度,涵道中心处速度可增大至原来的2倍。在导流涵道作用下,水轮机转矩脉动系数减小了0.474。水轮机与导流涵道的间距对效率与转矩产生了显著的影响,当间距为0.175倍水轮机直径时,其能源利用率达到最大,同时转矩系数在0.1倍直径时降至最小。     

预埋与绑扎埋管形式能量桩承载特性研究

预埋钢管能量桩是一种新型桩埋管形式的地源热泵技术;然而针对其特殊埋管形式下的承载特性的研究相对较少。针对预埋钢管单U型埋管能量桩的承载特性开展模型试验和数值模拟研究,测得在热-冷循环温度荷载作用下预埋钢管单U型埋管能量桩桩顶位移、桩体热应变及桩端阻力的变化规律;为了对比分析,同时进行传统绑扎单U型埋管能量桩的承载特性模型试验,并分析预埋钢管能量桩的适用性。研究结果表明,与传统绑扎单U型埋管形式相比,预埋钢管能量桩具有相对更优的承载性能;预埋钢管能量桩两种工况最终的桩顶位移比绑扎埋管能量桩分别小23%和13%,而桩体最大热应变分别仅为绑扎埋管能量桩的44%和25%,桩端阻力也分别比绑扎埋管能量桩小14%和35%。     

导流罩对潮流能水轮机效率提升分析

设置导流罩能提高潮流能水轮机效率,缩小转轮尺寸,降低机组造价。为了揭示导流罩聚能增效机理,采用VOF两相流模型对竖轴直叶潮流能水轮机进行三维模拟分析。即先根据模拟对象计算无导流罩情况下水轮机效率与尖速比的关系曲线,并对比加装导流罩前后的流态变化;然后分析导流罩各体型参数对水轮机获能效率的影响,通过正交分析得到使水轮机效率最高的体型。研究表明,导流罩通过提高转轮下游盘面流速来提高水轮机获能效率,其中导流罩喉部宽度对水轮机效率影响最大。     

旋向对竖轴潮流能水轮机阵列特性的影响分析

应用竖轴水轮机阵列水动力性能预报程序研究潮流能水轮机阵列水动力干扰现象。分析单体的相对旋转方向对其自身水动力响应以及对阵列整体获能效率的影响方式、影响程度和影响规律。研究表明:反向旋转水轮机组整体获能效率明显比同向旋转对应值高,水轮机间距越小,反向旋转的优势越明显。和同向旋转相比,反向旋转转子力矩系数均值大,对应的峰值高。较之于同向旋转情况,反向旋转情况下水轮机叶片合力均值略大。     

计入自由端扭矩输出的轴系扭振计算

某六缸直列柴油机自由端输出载荷增加,需要再次对曲轴的可靠性进行评估。我们运用Excite Designer搭建了曲轴一维仿真模型,通过改变曲轴自由端和飞轮端功率输出,得到各轴段扭振幅值及扭振应力的变化情况。计算结果表明:在增大自由端载荷输出后,曲轴各轴段扭振幅值没有变化,但是扭振应力均有不同程度的减小,曲轴趋于更加安全。     

A conceptual study of floating axis water current turbine for low-cost energy capturing from river,tide and ocean currents

The cost of utilizing kinetic energy of river stream, tidal and ocean current is considered to be higher than that of wind power generation because of difficulties in construction and maintenance of devices installed in seawater. As a solution to the problem, the authors propose a new concept of water stream turbine. The main idea is in the manner of supporting turbine. Although it is similar to a vertical axis turbine, the direction of turbine axis is not firmly fixed and its tilt angle is passively adjustable to the stream velocity. Since it does not have to keep the turbine axis in upright position, required structural strength and weight of the device will be reduced significantly. This paper describes the application ranging from the small hydro power in river streams to large application of tidal and ocean current turbine. In the large capacity plant for tidal stream and ocean current, the main mechanism of turbine axis support is the same as that of the wind turbine authors proposed in the previous paper. It leads to the further opportunity of cost reduction. The sample design of a multi-megawatt ocean current turbine shows the possibility of high economic performance of the concept. The results show that the cost of energy in the concept can be comparable to a land based wind turbine.     

垂直轴潮流能水轮机研究与利用现状

随着化石能源不断枯竭和环保要求的不断提高,世界各国对潮流能的开发利用愈加重视,垂直轴水轮机是潮流发电装置主要结构形式之一,本中介绍了垂直轴水轮机国内外利用现状和研究方法的进展情况,并指出垂直轴水轮机开发利用所需要解决和突破的技术难点和问题,为垂直轴水轮机开发利用指明了研究重点。     

垂直轴水轮机CFD数值模拟有效性验证

CFD方法作为垂直轴水轮机水动力性能预报和分析的一种重要手段,得到了广泛的应用,但是目前,对于垂直轴水轮机CFD数值模拟的精度和可信度缺乏系统的研究,因此针对这一问题,展开了垂直轴水轮机CFD数值模拟有效性研究,探讨了湍流模型、时间步长和网格尺度对计算结果的影响,并通过与试验结果的对比,验证了CFD方法的有效性,为以后CFD方法在垂直轴水轮机性能预报方面的应用奠定了基础.     

驱动热泵的垂直轴风力机风轮气动特性数值分析

根据风能热泵系统的工作环境及匹配特性,针对给定供热面积的系统各参数选取方法以及垂直轴风力机风轮设计进行了探讨,在此基础上初步完成了额定功率为300 W的风轮设计,并利用二维数值模拟方法对不同叶尖速比下的性能曲线进行计算,分析得到了额定风速9.00 m/s时,驱动压缩机的最佳风轮转速为350~375r/min。结果表明,300 W垂直轴风力机的输出特性可满足风能热泵机组的工作要求,该数值分析结果可为风能供热技术的应用示范提供理论支撑。     

Variability and phasing of tidal current energy around the United Kingdom

Tidal energy has the potential to play a key role in meeting renewable energy targets set out by the United Kingdom (UK) government and devolved administrations. Attention has been drawn to this resource as a number of locations with high tidal current velocity have recently been leased by the Crown Estate for commercial development. Although tides are periodic and predictable, there are times when the current velocity is too low for any power generation. However, it has been proposed that a portfolio of diverse sites located around the UK will deliver a firm aggregate output due to the relative phasing of the tidal signal around the coast. This paper analyses whether firm tidal power is feasible with ‘first generation’ tidal current generators suitable for relatively shallow water, high velocity sites. This is achieved through development of realistic scenarios of tidal current energy industry development. These scenarios incorporate constraints relating to assessment of the economically harvestable resource, tidal technology potential and the practical limits to energy extraction dictated by environmental response and spatial availability of resource. The final scenario is capable of generating 17 TWh/year with an effective installed capacity of 7.8 GW, at an average capacity factor of 29.9% from 7 major locations. However, it is concluded that there is insufficient diversity between sites suitable for first generation tidal current energy schemes for a portfolio approach to deliver firm power generation.     

聚风导流型立轴风力机设计及气动性能分析

针对传统的立轴风力机风能利用率低的问题,应用正交优化法和流场数值模拟技术对聚风导流型立轴风力机的结构设计参数进行了优化设计。在同尺度下与传统立轴风力机进行了对比分析。结果表明,聚风导流型立轴风力机叶轮的输出功率、风能利用率及自启动特性均得到了显著提高。     

基于正反装叶片的垂直轴潮流水轮机水动力性能分析

为了解不对称翼型叶片的正反安装对垂直轴潮流水轮机水动力性能的影响,运用CFD软件技术,建立了不对称叶片正反安装的潮流水轮机模型,分析了不对称叶片在正反两种安装方式下,叶片压力面和吸力面压力系数随叶片相位角不同而发生的变化,同时利用效率公式计算得到了效率。结果表明,叶片的正反安装对水轮机的水动力性能影响较大,当叶片正装即不对称翼型叶片凸向朝外时,垂直轴潮流水轮机效率优于叶片反装时,叶片在相位角为0°~120°区间转动时,转轮扭矩先增大后减小,在60°、180°、300°时得到最大扭矩。     

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.     

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.