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。     

基于烟线法的直线翼垂直轴风力机静态流场可视化试验

为探明直线翼垂直轴风力机自起动性能与风力机叶片迎风角度的关系,设计制作了一台具有3枚NACA0018翼型叶片的直线翼垂直轴风力机模型.通过风洞试验测试了直线翼垂直轴风力机在不同风速下自起动性与叶片迎风角度的关系;利用烟线法对风力机的静态流场进行了可视化试验,获得了不同叶片迎风角度下风力机周围流场的流迹线图像;分析了风力机自起动性与叶片翼型、叶片个数、叶片受力情况和周围流场的关系.     

叶片端板对垂直轴水轮机水动力性能影响的研究

为了减小叶片端部涡流的影响,提高叶片效率,在垂直轴潮流能水轮机叶片端部加装端板。使用Fluent软件对不同流速下加装端板前后的水轮机流场进行三维数值模拟,比较其水动力性能的变化,并通过拖曳水池进行物理模型实验验证。结果表明,为垂直轴水轮机叶片末端加装端板可抑制叶片端部涡流,提高水轮机输出功率。     

不同涡流发生器参数对潮流能水轮机翼型水动力学特性影响研究

将涡流发生器（VGs）流动控制理论引入到水轮机叶片设计领域,开展涡流发生器对潮流能水轮机叶片流动分离效应的抑制机理及水动力学特性研究。以NACA4418翼型为研究对象,分别建立基础翼型段和带VGs翼型段的潮流能水轮机翼型三维模型,应用CFD方法研究不同VGs排布方式、间距、高度以及长度参数对翼型段水动力性能的影响。结果表明：翼型段上安装VGs能有效减缓流动分离,合理的VGs排布方式可有效提高翼型的最大升力系数,正向排布优于反向排布,VGs间距为25 mm、高度为5 mm、长度为17 mm时对翼型段改善效果最佳,各组带VGs翼型最大阻力系数都增大约5%,翼型整体性能上升。利用水槽试验的方法验证仿真模型的准确性。此外,通过对翼型段进行二维流场分布以及VGs背流侧进行静压分布研究,进一步揭示VGs的作用机理。     

固定偏角垂直轴潮流能水轮机叶片安装位置试验研究

叶片安装位置是影响固定偏角垂直轴潮流能水轮机水动力性能的关键参数之一,为了研究其对水轮机性能影响的基本规律,建立了垂直轴水轮机水槽模型试验系统,设计了垂直轴水轮机性能和载荷测试方法。通过试验结果的分析,得到了叶片安装位置对水轮机能量利用率、推力系数、侧向力系数和合力系数的影响规律,为水轮机设计提供了试验依据。     

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%。     

潮流能水平轴水轮机翼型几何参数对其转捩特性的影响研究

边界层转捩对潮流能水轮机翼型的摩擦阻力、流动的分离位置等有较大影响,为了研究潮流能水平轴水轮机翼型的转捩特性,以NACA4418为初始翼型,采用控制变量法对初始翼型进行几何修形来研究不同厚度、不同弯度对潮流能水平轴水轮机翼型边界层转捩及其水动力学性能的影响。通过Fluent软件中的UDF功能将Michel转捩判据与γ-Reθ转捩模型相结合的经验关联值写入求解器中。通过计算,得到不同弯度和厚度的翼型转捩点位置随不同来流攻角的变化规律以及翼型表面的边界层转捩对其水动力学性能的影响规律。研究结果表明:典型工况下,来流攻角越大,翼型边界层转捩点位置随攻角的增大前移,相对厚度和相对弯度均会使转捩点向前缘移动,小攻角条件下弯度影响有减缓的趋势。     

垂直轴风力机动态流场及其气动性能分析

垂直轴风力机气动性能研究是风力机设计、实验的重要部分,对其运动状态下的流场进行分析是观测垂直轴风力机性能重要环节.基于NACA0012对称翼型,建立二维几何模型并进行模拟计算.采用k-ωSST湍流模型及滑移网格技术,通过CFD软件数值计算得到达里厄型直叶片垂直轴风力机运行时周边流场分布情况.通过比较不同方位角下流场涡量以及升、阻力系数得出:在方位角为105°附近时,翼型下表面产生流动分离,并导致失速;下风区翼型运行的流场由于受到上风区尾流的影响,翼型周围没有产生明显的流动分离.     

垂直轴风机叶片覆冰数值模拟及其气动性能研究

研究升力型垂直轴风机叶片的覆冰特性,为风机的防冰、除冰系统研发提供帮助。文章对垂直轴风机叶片的雾凇覆冰物理过程进行了分析,建立了风机叶片覆冰的数值计算模型。通过SST k-ω湍流模型求解旋转叶片周围的空气流场,利用拉格朗日法获得过冷却水滴的运动轨迹及碰撞情况,结合覆冰时间推进法得到叶片表面的覆冰形貌,并通过流场计算分析覆冰对风机气动性能的影响。利用该计算模型研究了不同叶片翼型、叶片数量以及叶尖速比λ对垂直轴风机叶片覆冰的影响。结果表明:当风机的λ增大时,风机叶片表面的覆冰更多的向叶片前缘尖端区域集中,叶片后缘的覆冰量减少;在同一覆冰条件下,不同叶片翼型、叶片数量和λ对垂直轴风机的整体覆冰量、单个叶片的覆冰量以及叶片表面的最大覆冰厚度均产生重要影响;不同叶片翼型、叶片数量和λ的风机的静态扭矩特性受覆冰影响差异大。     

并列式垂直轴水轮机尾流场的干扰特性研究

为研究并列式垂直轴水轮机的水动力性能及尾流干扰特性,进而指导阵列式水轮机的排列,文章对并列式垂直轴水轮机的水动力性能进行数值分析。首先针对单个垂直轴水轮机的水动力性能进行分析,基于数值分析结果与实验数据的对比,验证了所采用数值分析方法的准确性,继而对并列式垂直轴水轮机的性能进行了分析。分析结果表明:垂直轴水轮机的尾流具有明显的非对称现象,且尾流之间的干扰对尾流场的速度影响较大;由于水轮机尾流压力分布不均,两个水轮机尾流之间会产生压力差,进而导致尾涡向低压力区域偏移,整体表现为向迎流侧偏移;尾流继续传播扩散,最后与流场混合;在并列排布垂直轴水轮机时,应尽量使相邻水轮机处于顺流侧并反向旋转,当水轮机处于相邻水轮机的迎流侧时,应注意加大水轮机之间的间距。     

Lift correction model for local shear flow effect on wind turbine airfoils

Wind turbines operate under various wind conditions in which turbulence virtually always exists. Therefore, unsteady wind turbine simulation methods to estimate wind loading in turbulent inflow conditions are very important for developing optimally designed wind turbines. Several methods have been developed for this purpose and are usually based on the blade element momentum theory (BEMT), which is used for calculation of the wind loading on turbine blades. The local shear flow effect induced by turbulence, however, is not explicitly considered in the popular BEMT-based simulations. Extreme situations can occur in a large-scale wind farm where the inflow field of a wind turbine may contain strong tip vortices generated from upstream turbines. In this study, the effects of idealized local shear flows around a two-dimensional airfoil, S809, on its aerodynamic characteristics were analyzed by CFD simulations. Various parameters including reference inflow velocity, shear rate, angle of attack, and cord length of the airfoil were examined. From the simulation results, several important characteristics were found. The shear rate in a flow causes some changes in the lift coefficient depending on its sign and magnitude, while the angle of attack does not have a distinguishable influence. The chord length and reference inflow also cause proportional and inversely proportional changes in the lift coefficient, respectively. Based on these observations, we adopted an analytic expression for the lift coefficient from the thin airfoil theory and proposed a lift correction model, which is easily applicable to the traditional load analysis procedure based on the BEMT.     

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.     

直叶片动态效应水动力特性实验研究

文章通过水槽实验研究了直叶片在静态以及动态效应下的水动力特性。研究结果表明:在静态分析情况下,在来流加、减速过程中,直叶片的升、阻力系数的变化趋势相同;在动态分析情况下,当来流速度一定,电机转速不同时,直叶片的升、阻力系数在不同转速下的变化趋势基本相同;当电机转速一定,来流速度不同时,来流速度对叶片水动力性能的影响具有一致性;与静态分析相比,翼型的动态失速角大于静态失速角,失速延迟现象较为明显。实验结果可为直叶片动态失速现象的研究提供一定的参考价值。     

Influence of a velocity profile & support structure on tidal stream turbine performance

With tidal turbine technology in its infancy prototype devices are likely to be positioned at locations where both the local marine environment and vessel navigation are favourable. However, as marine turbine technology develops toward economic viability there is a propensity for undesirable interactions with local shipping, higher turbulence levels and velocity shear through the water column to occur. The latter high shear could result from positioning the turbine lower in the water column, perhaps due to local shipping requirements. This paper helps to elucidate the performance of the tidal turbine and in particular the blade forces during rotation within a high shear velocity profile. A velocity profile from ADCP measurements was used as an inlet boundary for CFD analysis. The work shows that the presence of a suitably positioned stanchion downstream of the turbine will result in reduced performance characteristics over a complete rotation. However, the amplitude of the characteristics, in particular, the axial loading increases which would require careful design considerations.     

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.     

Influence of blade deformation and yawed inflow on performance of a horizontal axis tidal stream turbine

For a better design of tidal stream turbines operated in off-design conditions, analyses considering the effects of blade deformation and yawed inflow conditions are necessary. The flow load causes deformation of the blade, and the deformation affects the turbine performance in return. Also, a yawed inflow influences the performance of the turbine. As a validation study, a computational fluid dynamics (CFD) simulation was carried out to predict the performance of a horizontal axis tidal stream turbine (HATST) with rigid blades. The numerical uncertainty for the turbine performance with blade deformation and a yawed inflow was evaluated using the concept of the grid convergence index (GCI). A fluid–structure interaction (FSI) analysis was carried out to estimate the performance of a turbine with flexible composite blades, with the results then compared to those of an analysis with rigid blades. The influence of yawed inflow conditions on the turbine performance was investigated and found to be important in relation to power predictions in the design stages.     

Aerodynamic Loading Distribution Effects on the Overall Performance of Ultra-High-Lift L Turbine Cascades简

The present paper reports the results of an experimental investigation aimed at comparing aerodynamic perform- ance of three low-pressure turbine cascades for several Reynolds numbers under steady and unsteady inflows. This study is focused on finding design criteria useful to reduce both profile and secondary losses in the aero-engine LP turbine for the different flight conditions. The baseline blade cascade, characterized by a standard aerodynamic loading （Zw=1.03）, has been compared with two Ultra-High-Lift profiles with the same Zweifel number （Zw=1.3 for both cascades）, but different velocity peak positions, leading to front and mid-loaded blade cascade configurations. The aerodynamic flow fields downstream of the cascades have been experimentally in- vestigated for Reynolds numbers in the range 70000〈Re〈300000, where lower and upper limits are typical of cruise and take-off/landing conditions, respectively. The effects induced by the incoming wakes at the reduced frequency ./＋=0.62 on both profile and secondary flow losses for the three different cascade designs have been studied. Total pressure and velocity distributions have been measured by means of a miniaturized 5-hole probe in a tangential plane downstream of the cascade for both inflow conditions. The analysis of the results allows the evaluation of the aerodynamic performance of the blade cascades in terms of profile and secondary losses and the understanding of the effects of loading distribution and Zweifel number on secondary flows. When operating un- der unsteady inflow, contrarily to the steady case, the mid-loaded cascade has been found to be characterized by the lowest profile and secondary losses, making it the most attractive solution for the design of blades working in real conditions where unsteady inflow effects are present.     

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。     

变叶片数和长短叶片对某跨音速向心汽轮机气动性能的影响

利用三维数值模拟的方法对一跨音速向心汽轮机进行了气动设计优化分析,通过改变叶片数和采用长短叶片结构等方法分析其对叶轮内流场的影响,分析了TC-4P叶型的气动特点。结果表明:TC-4P叶型虽然只是普通的渐缩型流道的叶栅,但利用其斜切部的膨胀能力,对超音速工况一样具有良好的性能;叶轮采用长短叶片的方法可以有效地降低余速损失,并改善流动状况。