Solar chimney turbine characteristics

A typical layout of a solar chimney power plant has a single axial turbine with radial inflow through inlet guide vanes at the base of the chimney. Turbine efficiency depends on the turbine blade row and turbine diffuser loss coefficients. The paper presents analytical equations in terms of turbine flow and load coefficient and degree of reaction, to express the influence of each coefficient on turbine efficiency. It finds analytical solutions for optimum degree of reaction, maximum turbine efficiency for required power and maximum efficiency for constrained turbine size. Characteristics measured on a 720 mm diameter turbine model confirm the validity of the analytical model. Application to a proposed large solar chimney plant indicates that a peak turbine total-to-total efficiency of around 90% is attainable, but not necessarily over the full range of plant operating points.     

Tests on ducted and bare helical and straight blade Darrieus hydrokinetic turbines

Despite much optimistic language on commercial websites, little data is available on actual performance of hydrokinetic turbines. This paper summarises the findings of a series of tests on several Darrieus type cross flow hydrokinetic turbines (HKTs). Although this type of hydrokinetic turbine (HKT) has some advantages over axial flow turbines, fixed pitch Darrieus HKTs also have some drawbacks, including inability to self-start under load, low efficiency and shaking. Variable pitch has been suggested to increase starting torque and efficiency, ducts to increase power output and helical blades to produce smooth torque. To assess each of these modifications, tests were conducted in Australia and Canada on HKTs with fixed and variable pitch straight blades, fixed helical blades, with and without a slatted diffuser, by mounting each turbine in front of a barge and motoring through still water at speeds ranging from less than 1 m/s up to 5 m/s. The diffuser increased the power output by a factor of 3 in one configuration but considerably less in others. A reason for this finding is suggested. The maximum coefficient of performance Cp of the fixed pitch straight blade and helical turbines without a diffuser ranged from about 0.25 at 1.5 m/s down to less than 0.1 at 5 m/s, while Cp for those with a diffuser ranged from about 0.45 down to about 0.3. Fixed blade turbines, both straight and helical, exhibited low starting torque, while variable pitch turbines started easily. Considerable differences in Cp were observed for the same turbine configuration at different speeds. The turbine with fixed pitch, straight blades was found to shake violently due to cyclical hydrodynamic forces on blades, while the helical and variable pitch turbines did not shake excessively. These findings suggest that variable pitch cross flow HKTs should be further investigated.     

振荡水柱波浪发电空气透平工作特性数值模拟

为更深入地探讨振荡水柱式波能发电装置的原理,对用于波力发电装置二次能量转换的威尔斯式透平进行了三维全流道模拟计算。针对对称翼型叶片和非对称翼型叶片的威尔斯式透平,分别考察了其在不同叶片安装角下的效率和出力随流量系数的变化趋势,得出了不同叶片安装角时威尔斯式透平运行的最佳参数。在相同工况下,对比分析了不同翼型叶片威尔斯式透平的效率、出力、输入系数及扭矩系数随流量系数的变化,并比较了叶片表面的压力分布情况。结果表明,随着叶片安装角增大,装置最高效率值增大,且在安装角大于9°后变化缓慢,而装置最大出力却随着安装角的增大而减小;采用非对称翼型叶片时,装置的出力、输入系数、扭矩系数均大于相同工况下对称翼型叶片装置。     

新型变桨立轴风力机涡效应分析

该文旨在通过变桨来改善升力型立轴风力机叶片气动特性,提高风力机最大运行效率。针对设计尖速比下风能利用系数较低的问题,提出减小叶片小攻角范围,增大叶片大攻角工作范围,以重点改善叶片低性能区域的气动特性为出发点,提高风能利用系数新变桨思路。以采用NACA0012翼型、2 m高和2 m旋转直径的两叶片H型风力机为研究对象,从涡理论来分析和比较在最佳尖速比为5的条件下,附着涡、尾随涡、脱体涡和桨距角对攻角、切向力和功率输出的影响规律。研究结果表明:变桨后,叶片的攻角、切向力和输出功率在原最大值两侧均有明显提高,拓宽了叶片高性能的工作区域;涡系中脱体涡对叶片气动特性影响最大,其中在上盘面影响较小,在下盘面影响较大;变桨前后涡系对上盘面的差异较小,对下盘面的影响差异较明显;变桨后,下盘面的叶片的涡尾迹弯曲程度在加大。     

尾水管扩散段结构变化对低水头混流式水轮机性能的影响

为探究低水头混流式水轮机尾水管扩散段底板抬起角对其性能的影响,结合西南某水电站增效扩容项目,在保证尾水管扩散段上下面角度不变的前提下,拟定了两套扩散段底板抬起角方案,利用相关软件建立了高效区内导叶开度为35°时水轮机的水体模型,并对其进行了流场数值模拟。结果表明,尾水管扩散段底板抬起角对水轮机效率影响不大,对水轮机出力和尾水管回能系数影响较大;随着底板抬起角的增加,相同水头下水轮机出力逐渐减小;在低水头(小流量)时,有适当的底板抬起角比没有时更有利。     

遗传算法在水平轴洋流机叶片优化设计中的应用

水平轴洋流机是捕获洋流能的主要设备,其叶片外形直接影响捕能效率。通过Bezier参数化曲线描述定速定桨距洋流机的叶片弦长和扭角分布规律,采用叶素-动量理论计算其水动特性。以额定流速下能量利用系数系数最大为目标,基于遗传算法建立了叶片外形优化模型。同时,为了避免因汽蚀导致功率输出不稳定的现象,在优化过程中以汽蚀作为约束条件,与经典设计方法Wilson理论设计叶片进行了比较。结果表明:优化叶片在叶根处的扭角更小,具有更佳的抗扭性能;叶根和叶尖处弦长均更小,节省了材料;在设计流速范围内,优化叶片在低流速下效率更高,平均提高了4.6%,具有更好的启动性能。     

Characteristics of a highly efficient propeller type small wind turbine with a diffuser

We studied the improved effects a diffuser had on the output power of small wind turbine systems, aiming to introduce these systems to radio relay stations as an independent power supply system. A frustum-shaped diffuser was chosen from an economical standpoint and wind speed distribution. The effect the diffuser's shape had on the wind speed was analyzed by simulation and showed that the wind speed in the diffuser was greatly influenced by the length and expansion angle of the diffuser, and maximum wind speed increased 1.7 times with the selection of the appropriate diffuser shape. The wind speed in the diffuser was fastest near the diffuser's entrance. We conducted field tests using a real examination device with a diffuser and confirmed that the output power of the wind power generator increased by up to 2.4 times compared to that of a conventional turbine. Moreover, it was confirmed that the diffuser was especially useful where the wind direction was constant.     

Experimental investigation of wake effects on wind turbine performance

The wake interference effect on the performance of a downstream wind turbine was investigated experimentally. Two similar model turbines with the same rotor diameter were used. The effects on the performance of the downstream turbine of the distance of separation between the turbines and the amount of power extracted from the upstream turbine were studied. The effects of these parameters on the total power output from the turbines were also estimated. The reduction in the maximum power coefficient of the downstream turbine is strongly dependent on the distance between the turbines and the operating condition of the upstream turbine. Depending on the distance of separation and blade pitch angle, the loss in power from the downstream turbine varies from about 20 to 46% compared to the power output from an unobstructed single turbine operating at its designed conditions. By operating the upstream turbine slightly outside this optimum setting or yawing the upstream turbine, the power output from the downstream turbine was significantly improved. This study shows that the total power output could be increased by installing an upstream turbine which extracts less power than the following turbines. By operating the upstream turbine in yawed condition, the gain in total power output from the two turbines could be increased by about 12%.     

带大小叶片楔形扩压器设计及流场分析

设计了两套双圆弧中线的叶片,并在此叶片基础上设计了11个大叶片＋11个小叶片的楔形扩压器.运用通用CFD软件FineTM/Turbo对其进行了流场分析.通过两扩压器的性能比较,初步确定了备用方案,进一步的优化设计对入选方案作了改进以满足微型燃气轮机总体设计要求.同时比较了大小叶片设计方案与全为大叶片方案的性能,发现采用大小叶片可提高静压恢复系数,降低空气动力损失.     

加装后缘小翼的垂直轴风力机输出特性研究

为了研究H型垂直轴风力机后缘加装小翼的输出特性变化规律,文章以NACA0012翼型叶片为例,采用风洞试验与数值模拟的方法,对加装后缘小翼的风力机进行了研究。模拟结果表明,加装后缘小翼的风力机的单叶片扭矩系数及功率性能要优于未加装小翼的风力机,整体功率较未加装小翼的风力机略有提升。风洞实验结果表明:加装后缘小翼可以提高风力机的最大输出功率,其中径长比对于加装小翼的垂直轴风力机功率提升的影响较大;当转速小于300 r/min时,安装径长比为0.6的后缘小翼的风力机输出功率最高;当转速超过300 r/min时,径长比为0.4的后缘小翼的风力机输出功率最高。     

Development of two-way diffuser for fluid energy conversion system

An experimental study was carried out to develop a new type of two-way diffuser suitable for a fluid flow energy conversion system. It is known that the power available from the fluid flow is proportional to the cube of the free stream velocity of the flow. Therefore, in order to take higher power output from the fluid flow, it is very important to construct a suitable system to increase the flow velocity. For a wind turbine, it has been reported that the speed of wind passing through it is dramatically increased by the use of a diffuser with a brim around the turbine. In this study, a new type of two-way diffuser suitable for a flow periodically changing its direction, such as a tidal current, was developed, applying the system to accelerate the wind speed for the wind turbine. The effects of the brim height and the outside body shape on the diffuser performance were experimentally investigated by measurement of the pressure and the velocity distributions along the center axis of the diffuser and around the diffuser. The present study is the first one to clarify the effect of these on diffuser performance.     

Characterization of aerodynamic performance of wind-lens turbine using high-fidelity CFD simulations

Wind-lens turbines (WLTs) exhibit the prospect of a higher output power and more suitability for urban areas in comparison to bare wind turbines. The wind-lens typically comprises a diffuser shroud coupled with a flange appended to the exit periphery of the shroud. Wind-lenses can boost the velocity of the incoming wind through the turbine rotor owing to the creation of a low-pressure zone downstream the flanged diffuser. In this paper, the aerodynamic performance of the wind-lens is computationally assessed using high-fidelity transient CFD simulations for shrouds with different profiles, aiming to assess the effect of change of some design parameters such as length, area ratio and flange height of the diffuser shroud on the power augmentation. The power coefficient (C_p) is calculated by solving the URANS equations with the aid of the SST k–ω model. Furthermore, comparisons with experimental data for validation are accomplished to prove that the proposed methodology could be able to precisely predict the aerodynamic behavior of the wind-lens turbine. The results affirm that wind-lens with cycloidal profile yield an augmentation of about 58% increase in power coefficient compared to bare wind turbine of the same rotor swept-area. It is also emphasized that diffusers (cycloid type) of small length could achieve a twice increase in power coefficient while maintaining large flange heights.     

浅析水平轴风力机叶片设计叶尖速比的选择

设计叶尖速比是风力机叶片设计中需要考虑的重要因素,文中分析了叶尖速比对叶片的弦长、载荷、气动性能、整机的功率和发电量等的影响,讨论了设计叶尖速比的选择。并分析得出增大设计叶尖速比,能够减小叶片弦长、载荷、成本,提高气动性能,但会使机组发电量有所下降的结论。     

Performances of ideal wind turbine

If there is an ideal wind turbine, its performances will be the pursuit goals for designing the actual wind turbine. In this paper, the wind turbine that has the maximum efficiency is defined as ideal wind turbine, which has three main features: lift-drag ratio is infinite, it has enough number blades so that the blade tip and root losses can be ignored, and its blades are limited in width. Using blade element theory, the differential equations of power, torque, lift and thrust of blade element were derived, and the expressions of power, torque, lift and thrust coefficients of the ideal wind turbine were gained by integrating along the blade span. Research shows that the power, torque and lift coefficients of the ideal wind turbine are functions of tip-speed ratio. When the lift-drag ratio and the tip-speed ratio is approaching infinity, power coefficient of the ideal wind turbine is close to the Betz limit; The torque limit is 0.401 when the tip-speed ratio equals about 0.635; The Lift limit is 0.578 when the tip-speed ratio equals about 0.714; The thrust coefficient is 8/9, which is unrelated with tip-speed ratio. For any wind turbine which tip-speed ratio is less than 10, the power coefficient is unlikely to exceed 0.585, for any high-speed wind turbine which tip-speed ratio is greater than 6, the torque coefficient in steady state is unlikely to exceed 0.1, and the lift coefficient is unlikely to exceed 0.2.     

Optimization of Savonius turbines using an obstacle shielding the returning blade

Due to the worldwide energy crisis, research and development activities in the field of renewable energy have been considerably increased in many countries. In Germany, wind energy is becoming particularly important. Although considerable progress has already been achieved, the available technical design is not yet adequate to develop reliable wind energy converters for conditions corresponding to low wind speeds and urban areas. The Savonius turbine appears to be particularly promising for such conditions, but suffers from a poor efficiency. The present study considers a considerably improved design in order to increase the output power of a Savonius turbine with either two or three blades. In addition, the improved design leads to a better self-starting capability. To achieve these objectives, the position of an obstacle shielding the returning blade of the Savonius turbine and possibly leading to a better flow orientation toward the advancing blade is optimized. This automatic optimization is carried out by coupling an in-house optimization library (OPAL) with an industrial flow simulation code (ANSYS-Fluent). The optimization process takes into account the output power coefficient as target function, considers the position and the angle of the shield as optimization parameters, and relies on Evolutionary Algorithms. A considerable improvement of the performance of Savonius turbines can be obtained in this manner, in particular a relative increase of the power output coefficient by more than 27%. It is furthermore demonstrated that the optimized configuration involving a two-blade rotor is better than the three-blade design.     

气冷涡轮转子变叶尖间距性能试验及数值研究

为量化评估工程应用的气冷低压涡轮带冠转子叶片的叶尖间距大小对涡轮气动性能的影响,综合现有涡轮部件试验能力,以单级轴流低压涡轮性能试验件为基础,通过控制圆度的机加方式磨削转子外环内壁以实现叶尖间距的变化,采用控制冷气流量比的方法,开展5次不同叶尖间距大小的涡轮级性能试验,得到多工况下涡轮效率、换算流量和换算功率等特性参数。采用加载冷气及考虑转子叶冠结构的数值模型进行三维仿真计算,并与试验结果对比分析。研究表明：叶尖间距由0.6 mm增加至3.2 mm,低压涡轮流通能力增大1%,叶冠泄漏量增多3.4%,但做功能力下降2.3%。涡轮效率变化与叶尖间距大小近似呈线性关系,叶尖间距每增加1 mm,效率约降低0.7%,同时,叶尖间距的增加导致了叶冠腔的旋涡结构、气流掺混及主流入侵强度逐渐增大,引起动叶总压损失的增大,叶尖间距增加至3.2 mm导致叶间位置总压损失由0.88增至2.3。     

Numerical optimization of axial turbine with self‐pitch‐controlled blades used for wave energy conversion

Wells turbines are among the most practical wave energy converters despite their low aerodynamic efficiency and power produced. It is proposed to improve the performance of Wells turbines by optimizing the blade pitch angle. Optimization is implemented using a fully automated optimization algorithm. Two different airfoil geometries are numerically investigated: the standard NACA 0021 and an airfoil with an optimized profile. Numerical results show that each airfoil has its own optimum blade pitch angle. The present computational fluid dynamics optimization results show that the optimum blade pitch angle for NACA 0021 is +0.3° while that of the airfoil with an optimized profile equals +0.6°.The performance of the investigated airfoils is substantially improved by setting the blades at the optimum blade pitch angle. Both the turbine efficiency and tangential force coefficient are improved, especially at low flow rate and during turbine startup. Up to 4.3% average increase in turbine efficiency is achieved by optimizing the blade pitch angle. A slight improvement of the tangential force coefficient and decrease of the axial force coefficient are also obtained. A tangible increase of the stall‐free operating range is also achieved by optimizing the blade pitch angle. Copyright © 2013 John Wiley & Sons, Ltd.     

先进的具高出力的核电汽轮机

介绍了西门子设计制造先进大功率核电汽轮机的长期运行经验,并发展半速饱和蒸汽核电汽轮机,功率达1700MW,末级长叶片高度为1829mm,从设计、工艺、材料选择等方面论述了提高机组出力、提高机组效率、减少腐蚀的方法,其中包括套装叶轮设计、3DSTM叶片技术、高压透平和低压透平等。     

Modeling turbine wakes and power losses within a wind farm using LES: An application to the Horns Rev offshore wind farm

A modeling framework is proposed and validated to simulate turbine wakes and associated power losses in wind farms. It combines the large-eddy simulation (LES) technique with blade element theory and a turbine-model-specific relationship between shaft torque and rotational speed. In the LES, the turbulent subgrid-scale stresses are parameterized with a tuning-free Lagrangian scale-dependent dynamic model. The turbine-induced forces and turbine-generated power are modeled using a recently developed actuator-disk model with rotation (ADM-R), which adopts blade element theory to calculate the lift and drag forces (that produce thrust, rotor shaft torque and power) based on the local simulated flow and the blade characteristics. In order to predict simultaneously the turbine angular velocity and the turbine-induced forces (and thus the power output), a new iterative dynamic procedure is developed to couple the ADM-R turbine model with a relationship between shaft torque and rotational speed. This relationship, which is unique for a given turbine model and independent of the inflow condition, is derived from simulations of a stand-alone wind turbine in conditions for which the thrust coefficient can be validated. Comparison with observed power data from the Horns Rev wind farm shows that better power predictions are obtained with the dynamic ADM-R than with the standard ADM, which assumes a uniform thrust distribution and ignores the torque effect on the turbine wakes and rotor power. The results are also compared with the power predictions obtained using two commercial wind-farm design tools (WindSim and WAsP). These models are found to underestimate the power output compared with the results from the proposed LES framework.     

叶片工程图纸智能快速生成技术的研究与实现

为了提高汽轮机叶片设计和出图的效率,在分析叶片零件特殊复杂性的基础上,提出了智能化自动生成工程图纸的方法,并在三维软件平台上开发了叶片工程图纸生成系统,进行验证。结果表明,提出的技术方法提高了叶片工程图纸的生成效率,极大地减少了生产过程中修改的工作量。