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。     

垂直轴风力机非对称翼型叶片变攻角方法

分析了H型垂直轴风力机非对称翼型叶片在一定雷诺数下的升力系数和阻力系数的变化,给出了叶片攻角的合理变化范围。通过分析风轮旋转一周叶片攻角的变化,给出了不同叶尖速比下叶片攻角随其方位角变化的规律。利用Origin软件计算出上下风区叶片的安装角与攻角的对应关系,并确定合适的安装角。分析表明,通过改变风轮叶片的安装角来调整叶片的攻角,能使风力机始终保持较高的功率输出。     

尾缘加厚翼型的三维旋转特性研究

采用计算流体动力学(CFD)方法对MEXICO试验风力机叶片不同部位翼型在旋转状态下的升阻力系数进行计算,并与试验数据进行比较分析,验证了CFD方法能够准确预测翼型在旋转状态下的升阻力系数。通过采用尾缘对称加厚到5%翼型弦长的DU 97-W-300-05翼型和对应的尾缘未加厚的DU 97-W-300翼型设计,得到沿叶片径向具有相同弦长的风力机叶片,并采用CFD方法对该叶片在旋转状态下的气动特性进行计算。结果表明:在旋转状态下,当攻角小于15°时,尾缘加厚翼型的升力系数比相对应的尾缘未加厚翼型大10%左右;尾缘加厚翼型在旋转状态下的粗糙度敏感性好于相对应的尾缘未加厚翼型;随半径增大,尾缘加厚翼型和对应的尾缘未加厚翼型的升力系数都增大,但失速提前,尾缘加厚翼型升力系数增大得更明显。     

叶片安装角对H型垂直轴风力机气动性能的影响研究

通过对直叶片垂直轴风力机在不同翼型、尖速比和实度组合状态下改变其叶片安装角得到的模型进行流场计算,总结以上3种情形下不同安装角对直叶片垂直轴风力机气动性能的影响:在以上3种情形下,负安装角对其气动性能不利;最佳气动性能安装角为1°~3°;安装角对其性能的影响相对有限(NACA0015,尖速比λ=1.5时,功率系数CP值从31.3%增加到34.5%),翼型厚度对气动性能的影响较大(21%厚度翼型,其C_P值约为40%),欲得到更好的CP值,最好通过改变翼型或增加翼型厚度来实现;当叶片翼型的相对厚度较小或工况为高尖速比下时,有必要通过改变安装角改善风力机的性能。     

后掠式水平轴潮流能水轮机的载荷与获能特性研究

针对双向潮流能有效利用问题,设计一种基于对称翼型的新型后掠式水平轴潮流能水轮机,并研究其水动力性能。根据对称翼型升阻力特性与叶片展向攻角变化,采用变截面设计优化后掠式对称翼型叶片,并基于Buhl修正模型分析不同后掠偏移叶片所受推力与获能特性。通过3D建模与水槽实验,研究不同后掠偏移叶片的载荷与获能情况。模型实验研究表明,同一尖速比下,后掠偏移量为10%和15%的水轮机相对于偏移量为5%的水轮机所受推力最大分别降低4%和13.3%,获能效率最多分别减小3.8%和11.1%,其中推力比获能效率减幅更大。实验结果与理论分析变化趋势吻合,但减幅比理论值偏高。此外,该水轮机3种后掠偏移量下对应获能效率随桨距角的增大分别降低18%、14%和6%,获能效率下降显著,与300 kW样机实海况运行情况变化趋势相同。     

风力机翼型尾缘加厚修型优化

为实现风力机专用翼型尾缘加厚修型优化,并实现优化过程的自动运行,采用ISIGHT多学科设计优化软件平台,针对钝尾缘翼型的运行特点,用切向和法向载荷系数描述翼型气动性能,基于指数混合函数法,提出翼型尾缘对称和非对称加厚优化问题,以尾缘加厚厚度为优化变量对风力机专用DU91-W2-250翼型的尾缘进行对称和非对称加厚修型优化。在ISIGHT软件平台上集成翼型生成、ICEM网格划分、Fluent流场计算、载荷计算以及遗传算法优化计算模块。优化结果表明,翼型尾缘对称和非对称加厚优化后其代表风力机叶片出力能力的切向载荷获得明显提高。翼型尾缘对称加厚优化的效果优于尾缘非对称加厚的情况。     

叶片副翼摆角对两段式翼型气动性能的影响

以Spalart-Allmaras(S-A)湍流模型为计算模型,对风力机叶片NACA0018翼型在副翼摆角分别为0°、5°、10°和15°下的流体流动情况进行数值模拟,分析不同攻角下带副翼翼型上升阻力性能曲线以及翼型表面压力分布云图和流场流线图,研究不同摆角对带副翼翼型的空气动力学性能的影响。结果表明:相同攻角时,翼型的升力系数随着副翼摆角的增大而减小;副翼摆角的增大可以增大翼型的失速攻角,改善翼型周围流体的流动状况,提高翼型周围特别是副翼周围流体流动稳定性,抑制流动分离涡的形成。     

风力机双层叶片式翼型气动性能

为了提高风力机的发电效率,优化风机叶片的翼型,以NREL研发的S809翼型为优化对象,设计了双层叶片翼型模型,利用Auto CAD软件建立了双层叶片翼型的几何模型。采取计算流体力学方法(CFD方法),对0~25.21°等26个攻角下双层叶片翼型进行气动计算,对其附近流场的流线图、压力分布云图、压力系数分布进行了分析,并与S809基准翼型进行了比较。结果表明:双层叶片翼型使叶片在不增加翼展的情况下增大升力;相比S809基准翼型,双层叶片翼型将失速攻角增加了6°;最大升力系数在S809翼型1.059的基础上增大到了1.363,研究结果为今后双层叶片翼型的研究打下了基础。     

垂直轴潮流能水轮机不同翼型叶片空化规律

为研究垂直轴水轮机叶片翼型形状对叶片空化的影响,采用数值模拟方法,对相同条件下相同相对厚度不同相对弯度的翼型,以及相同相对弯度不同相对厚度的翼型做了空化仿真。仿真结果表明,相同相对厚度不同相对弯度的薄、厚两种翼型,随着相对弯度增大,空化现象越易出现。相同相对弯度不同相对厚度的对称、相对弯度不为零的两种翼型,随着相对厚度增大,空化现象越易出现。同时监测了不同情况下翼型的升力系数和阻力系数,考虑到空泡的出现对翼型升力和阻力有所影响,将能量转化参数中的升力系数、阻力系数和升阻比与空化性能结合起来讨论。并将翼型按照相对弯度与相对厚度分组,分别探讨了相对弯度和相对厚度对翼型空化的影响规律,翼形相对厚度相同时,相对弯度越大,或者翼形相对弯度相同,相对厚度越大,则更容易空化。     

一种垂直轴螺旋形风力叶轮附近的三维湍流特征

以FIN翼型作为基本翼型,设计了一种垂直轴螺旋形风力叶轮。运用商用CFD软件Fluent对叶轮附近的三维湍流场进行了非定常数值模拟,分析了基本截面在不同迎风角度下的受力特征,获得了在最大力矩系数工况下流场中的流速和压力系数分布,并对比分析了不同扭角时的力矩系数。研究结果表明:采用不同迎风角度基本截面上的合力方向有较大差别,整个叶片上的力构成了复杂的力系;在最大力矩条件下,随着叶轮高度的变化,叶轮内的气流扩散区逐渐增大,压力系数分布逐渐减小;在不同叶片扭角条件下,力矩系数在叶轮旋转过程中的波动特征不同,90°叶片扭角力矩波动幅度较小,运行相对稳定。     

Effect of guide vanes on the performance of a self-rectifying air turbine with constant and variable chord rotors

A Wells turbine is a self-rectifying air flow turbine capable of converting pneumatic power of the periodically reversing air stream in Oscillating Water Column into mechanical energy. The Wells turbine has inherent disadvantages; lower efficiency, poorer starting characteristics, higher axial force and low tangential force in comparison with conventional turbines. Guide vanes before and after the rotor suggest a means to improve the tangential force, hence its efficiency. Experimental investigations are carried out on a Wells turbine with the constant chord and variable chord blade rotors fitted with inlet and outlet guide vanes to understand the aerodynamics. Experiments were also conducted for the above said rotors with various stagger angles to validate the design stagger angle. In addition, the starting and running characteristics of the rotors have been studied and compared with the case without guide vanes. Studies were done at various flow coefficients covering the entire range of flow coefficients over which the turbine is operable. The efficiency, starting characteristics of the turbines with guide vanes have improved when compared with the respective turbines without guide vanes.     

可变叶片安装角立轴风力机的转动力矩计算

为提高市轴风力机的效率,对可变叶片安装角的立轴风力机进行了分析,根据机翼升力与阻力的理论,在固定来流风速和旋转速度下计算了叶片在每个方位角上产生力矩最大的最佳安装角的变化规律,为了更好的运行,对最佳安装角的变化规律进行了一定修改.计算比较了固定安装角度的叶片与可变安装角度的叶片旋转一周产生的力矩,结果表明叶片在最佳安装角下运行时,每一转的正力矩都有明显增大,平均力矩町提高14倍.多个叶片在最佳安装角下运行时的力矩变化较平稳.可变叶片安装角立轴风力机是一种有发展前途的动力设备.     

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.     

Wells turbine blade profile optimization for better wave energy capture

Despite the fact that wave energy is available at no cost, it is always desired to harvest the maximum possible amount of this energy. The axial flow air turbines are commonly used with oscillating water column devices as a power take‐off system. The present work introduces a blade profile optimization technique that improves the air turbine performance while considering the complex 3D flow phenomena. This technique produces non‐standard blade profiles from the coordinates of the standard ones. It implements a multi‐objective optimization algorithm in order to define the optimum blade profile. The proposed optimization technique was successfully applied to a biplane Wells turbine in the present work. It produced an optimum blade profile that improves the turbine torque by up to 9.3%, reduces the turbine damping coefficient by 10%, and increases the turbine operating range by 5%. The optimized profile increases the annual average turbine power by up to 3.6% under typical sea conditions. Moreover, new blade profiles were produced from the wind turbine airfoil data and investigated for use with the biplane Wells turbine. The present work showed that two of these profiles could be used with low wave energy seas. Copyright © 2017 John Wiley & Sons, Ltd.     

Impact of Stagger Angle Nonuniformity on Turbine Aerodynamic Performance

The assembling error may lead to variation in stagger angles, which would affect the aerodynamic performance of the turbine. To investigate this underlying effect, two parallel numerical experiments on two turbines with the same profile, but uniform and nonuniform vane stagger angle respectively, were conducted in both steady and un- steady methods. The results indicate that certain changes in the detailed flow field of the turbine occur when the stagger angles are nonuniform, further, the blade loading distribution of the vane and rotor become markedly dif- ferent from that in uniform vane stagger angle situation. Then these consequences caused by nonuniformity men- tioned above enhance the unsteadiness of the flow, finally, the aerodynamic performance changes dramatically. It also shows that, compared with steady simulation, the unsteady numerical simulation is necessary in this investigation     

A modified Wells turbine for wave energy conversion

The method of wave energy conversion utilises an oscillating water column (OWC). The OWC converts wave energy into low-pressure pneumatic energy in the form of bi-directional airflow. Wells turbine with its zero blade pitch setting has been used to convert this pneumatic power into uni-directional mechanical shaft power. Measurements in OWC based wave energy plants in India and Japan show that the airflow velocity is not equal in both directions. The velocity is more when the airflows out to the atmosphere (exhalation) than in the reverse direction. It may be advantageous to set the rotor blade pitch asymmetrically at a positive pitch so as to achieve a higher mean efficiency in a wave cycle. Towards this objective, performance characteristics of a turbine with different blade setting angles in steady flow were found by experimentation. Quasi-steady analysis was then used to predict the mean efficiency for a certain variation of air velocity with time. This variation with time was taken as pseudo-sinusoidal wherein the positive part of the cycle was taken as a half sine-wave whose amplitude is greater than that of the negative half sine-wave. Such a variation is representative of what happens in reality. For exhalation velocity amplitude to inhalation velocity ratios 0.8 and 0.6, a rotor blade setting angle of 2° was found to be optimum.     

双层翼水平轴风力机气动性能研究

以NREL Phase VI风力机叶片为参照对象,设计一种双层翼叶片.在不同来流风速下,对该新型水平轴风力机叶片气动性能进行数值模拟,对比原始NREL Phase VI风力机在相同来流风速相同叶片高度处的流线图,发现双层翼叶片可较有效抑制流动分离.进一步将双层翼风力机叶片的扭矩值、弯矩值分别与相同条件下NREL Pha...     

Hysteretic characteristics of Wells turbine for wave power conversion

A Wells turbine blade for wave power conversion has hysteretic characteristics in a reciprocating flow. The hysteretic loop is opposite to the well-known dynamic stall of an airfoil. In this paper, the mechanism of the hysteretic behavior was elucidated by an unsteady 3-dimensional Navier-Stokes numerical simulation. It was found that the hysteretic behavior was associated with a streamwise vortical flow appearing near the blade suction surface. And also the effects of solidity, setting angle and blade thickness on the hysteretic characteristics of the Wells turbine have been discussed.     

Performance of an impulse turbine with fixed guide vanes for wave power conversion

A simple fixed geometry impulse turbine has been studied as a suitable power converter in Oscillating Water Column based wave power plants. Comparison with the Wells turbine, which is the commonly used self-rectifying turbine in such applications, shows it to be superior in performance under irregular flow conditions. Optimum guide vane angle for maximum efficiency has been arrived at based on the five angles tested.