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。     

叶片前缘偏转对H型垂直轴水轮机性能的影响

为提高传统直叶片升力型（H型）垂直轴水轮机的获能效率,提出一种带前缘可偏转叶片的新型垂直轴水轮机,利用计算流体力学（CFD）方法,结合重叠网格和动网格技术对这种新型垂直轴水轮机叶轮的水动力性能进行系统的数值模拟计算,分析不同叶尖速比下带前缘偏转叶片的垂直轴水轮机绕流流场,从而探究前缘偏转角度和偏转长度对这种水轮机动力性能和获能效率的影响规律。结果表明,根据叶片旋转到不同位置时实施前缘偏转可改变来流攻角从而减缓或抑制叶片吸力面的流动分离,有效改善其动态失速特性,进而使H型垂直轴水轮机的水动力性能和获能效率得到明显提升。研究发现,低叶尖速比下这种改善效果最为显著,可拓宽H型垂直轴水轮机高效运行的工作范围。     

风剪切来流下风力机叶片表面压力的分布规律

以某33 kW两叶片水平轴风力机的风轮和NREL PhaseⅥ风力机叶片为研究对象,数值模拟得到均匀来流条件下NREL PhaseⅥ风力机叶片表面压力系数的分布规律并与实验值进行对比,验证数值计算方法的有效性。在此基础研究不同风剪切来流对风力机叶片表面压力的影响及风剪切来流下叶片表面压力随方位角的变化规律。结果表明:当风剪切指数由0.3增至0.5时,叶片表面压力在不同方位角下发生不同的变化;剪切来流下,在叶片压力面和吸力面未发生流动分离的区域,压力随方位角呈现正余弦的变化趋势,越靠近尾缘,压力的波动幅度越小;在吸力面压力最小值的位置压力随方位角的波动幅度最大;在叶片吸力面发生流动分离的区域,压力随方位角的波动不稳定;无论是压力面还是吸力面,压力随方位角的变化均存在相位滞后现象,越靠近叶根,滞后现象越明显。     

基于BEM与CFD数值模拟的风力机叶片气动性能分析

为阐明转子叶尖损失效应以及动态失速效应对风力机气动性能预测的影响,文章采用计算流体力学(CFD)以及叶素动量理论(BEM)两种方法分析预测了不同风场条件下的叶片气动性能,研究了三维旋转效应下叶片表面的非定常气动特性。结果表明:在离心力和科氏力作用下,叶片吸力面发生流动分离,随着风速的增加,失速区域逐渐增大;叶片翼型截面前缘吸力侧受风速影响较大;在非定常来流条件下,叶尖部位尤其是前缘对来流敏感程度较高。通过不同叶尖损失校正模型对叶片载荷的预测结果对比可以看出,针对BEM进行的叶根叶尖修正计算结果更接近于CFD模拟结果,但是,在叶根和叶尖部位仍存在一定偏差。     

实海况下流速梯度对潮流能水轮机水动力性能影响的数值研究

针对实海况条件下来流梯度,基于现场实测的流速和水深数据,对实尺度水平轴潮流能水轮机的水动力学性能进行仿真,对比水轮机在流速梯度影响下获能和轴向力变化规律。结果表明,真实潮流场中流速梯度不仅对水轮机的获能和轴向力产生影响,还会造成流场的布放水深对水轮机实际获能产生影响。同时,流速梯度造成水轮机运行时所受载荷发生动态变化,使得叶片处于不同位置时轴向力和转矩呈现周期性波动,影响叶片的获能和动力稳定性,引起振动和寿命疲劳等问题。     

叶根倒角对轴流压气机转子两端区流动结构的影响研究

为了揭示叶根倒角对跨音速转子的气动性能影响规律,以NASA的Rotor67转子为研究对象,采用数值方法研究了叶根倒角对跨音速轴流压气机角区分离和工作裕度的影响机制。结果表明：叶根倒角的引入改善了叶片倒角区前缘附近的来流攻角适应性及该区域的叶型几何曲率分布特征,进而提升叶根吸力面的抗分离能力。带有倒角结构的转子叶片在其叶根倒角未覆盖区的叶型中后段周向压力梯度大于原型叶片,有利于克服气流沿吸力面流动时产生的离心力,进而抑制了尾缘附近的分离现象,使得该区域效率提升了3.9%以上。倒角的存在借助于径向平衡约束,重塑了叶尖区域的沿程叶表静压分布,并减小了尖区的入口轴向速度,直接导致叶尖区域主流流体的通流能力明显削弱,并诱发相对更强的间隙泄漏流,从而使得跨音转子提前发生失速,压气机工作裕度降低了19%以上。     

三维旋转效应对风力机叶片水滴收集率的影响分析北大核心CSCD

在进行风力机结冰问题的水滴收集率计算时,三维旋转效应的作用会改变叶片周围空气和水滴的流动,从而大大改变叶片气动性能和表面水滴收集。文章以NREL Phase VI风力机为研究对象,基于欧拉两相流模型对水滴流动及表面撞击特性进行计算,并与准三维计算结果进行比较,分析三维旋转效应对水滴绕流和收集率的影响。分析结果表明:在同一展向位置,三维旋转效应的存在会增加叶片表面最大水滴收集率及吸力面的水滴撞击区域,但对压力面水滴撞击区域的影响不明显;叶片表面的展向流动会将边界层内的水滴沿展向抽出,抑制水滴相流动分离及涡的形成,弦向流动会将主流区的水滴吸入边界层内,增大边界层内水滴的体积分数;三维旋转效应对水滴相流动及水滴收集率的影响在叶根附近较大,沿叶片展向方向的影响逐渐减弱。     

多工况条件下变叶片数潮流能水轮机能量及流动特性研究

文章建立了潮流能水轮机水动力性能数值计算模型,通过实验验证了利用该模型预测水轮机尾流的准确性,并利用该模型研究了潮流能水轮机在不同叶片数和不同叶尖速比条件下的能量和流动特性。研究结果表明:该数值计算模型在预测尾流速度亏损和湍流强度方面具有较好的精度,尤其在远尾流区,数值计算结果与实验结果保持一致;当叶尖速比(TSR)为4.5左右时,3叶片和4叶片的潮流能水轮机具有相对较高的获能系数,此结果对于水平轴潮流能水轮机的设计具有一定的指导意义。     

柔性叶片水轮机力学性能测算方法研究

针对一种新型潮流能发电获能装置--柔性叶片水轮机,采用风浪流水槽模型试验和Fluent数值模拟两种方法测算水力学性能参数,分析了两者测算结果的差异,并通过数值模拟法测算了柔性叶片水轮机力学特性,方法简便,对柔性叶片水轮机的开发利用具有指导意义.     

涡流发生器设计参数对某40%厚度翼型性能影响的实验研究

涡流发生器（VG或VGs）经常作为被动式的流动控制措施用于风力机叶片内侧,以减轻流动分离对气动性能的影响。然而,对内侧大厚度和极大厚度翼型,VG流动的复杂性和强烈的非定常性给基于数值模拟的VG设计和性能评估带来很大的不确定性。本文基于某相对厚度40%的大厚度钝后缘风力机翼型,在西北工业大学NF-3低速翼型风洞开展了涡流发生器设计参数对大厚度翼型表面流动和气动性能影响的试验研究。通过对气动特性、特征参数和压力分布等的分析可看出,VGs有效地改善了目标翼型的流动分离,提高了翼型性能;在设计参数中,弦向安装位置和涡流发生器高度对性能影响最大。     

涡流发生器形状对DU91-W2-250翼型动态失速的影响机理分析

以DU91-W2-250翼段为研究对象,分析不同形状涡流发生器（VGs）对动态失速的影响规律。结果表明：改变VGs形状参数对增升效果影响较大,对减阻效果影响较小,矩形VGs增升减阻效果更佳。从作用机理看,影响流动控制的主要是VGs流向涡涡流强度。矩形VGs气动性能提升效果明显最佳。矩形VGs流向涡在x/c=0.30~0.50范围内边界层内外流动掺混剧烈,抑制流动分离效果更佳。     

吸气控制策略对垂直轴风力机气动性能影响研究

针对垂直轴风力机复杂气动特性,将吸气孔置于风力机翼型上下表面,提出不同吸气控制策略以改善其气动性能。基于CFD方法,研究不同叶尖速比下吸气策略对风力机风能利用率、叶片切向力系数及流场特性的影响,综合考虑能量消耗与风力机输出功率。结果表明：提出的3种控制策略在低叶尖速比下均能大幅提升整机气动效率。效果最佳的迎、背风区交替吸气策略可显著推迟分离点,延缓翼型动态失速发生,并减少分离涡周期性脱落造成的损失。此外,该策略对动态尾迹效应有良好的控制效果,同时降低整机转矩波动幅值,消除中低叶尖速比下风轮负转矩,从而提高获能效率且延长风力机使用寿命。     

Numerical investigation of the effects of ITD length on low pressure nozzle

The advantage of high efficiency,low SFC (Specific Fuel Consumption),ultra-high bypass ratio turbofan engine attracts more and more attention in modem commercial engine.The intermediate turbine duct (ITD),which connects high pressure turbine (HPT) with low pressure turbine (LPT),has a critical impact on the overall performance of turbine by guiding flow coming from HPT to LPT without too much loss.Therefore,it becomes more and more urgent to master the technique of designing aggressive,even super-aggressive ITD.Much more concerns have been concentrated on the duct.However,in order to further improve turbine,LPT nozzle is arranged into ITD to shorten low pressure axle.With such design concept,it is obvious that LPT nozzle flow field is easily influenced by upstream duct structure,but receives much less interests on the contrary.In this paper,numerical method is used to investigate the effects of length of ITD with upstream swirl blades on LPT nozzle.Nine models with the same swirl and nozzle blades,while the length of ITD is the only parameter to be changed,will be discussed.Finally,several conclusions and advices for designers are summarized.After changing axial length of ducts,inlet and outlet flow field of nozzle differs,correspondingly.On the other hand,the shearing stress on nozzle blade (suction and pressure) surface presents individual feature under various inlet flow.In addition to that,"Clocking-like effect" is described in this paper,which will contribute much to the pressure loss and should be paid enough attention.     

基于CFD混流式水轮机上冠转轮泵结构优化研究

为研究中高水头混流式水轮机上冠转轮泵工作特性及优化可行性,以红山嘴一级电站3号水轮机为例,建立现转轮泵及11种结构优化模型,利用CFD商业软件,基于SST湍流模型对不同结构转轮泵在9种流量工况下展开数值模拟。将上冠流道泄漏水流动特性、主轴密封真空度及转轮泵效率作为研究指标,结果表明：上冠流道泄漏水流动特性依赖于转轮泵的结构类型;减小转轮泵“泵盖高度比”或斜置动泵叶对提高主轴密封真空度均有显著效果(最佳结构可提高66.9%),同时须兼顾其工作效率;额定工况下,转轮泵工作效率较低,建议转轮上冠开设合适的泄水孔补给流量提高其效率;该电站可将泵叶斜置45°、泵盖高度比H_p=0.0543的转轮泵作为最佳改进方案。     

Increase in the annual energy production due to a retrofit of vortex generators on blades

The aim of the current work was to analyze the effect of retrofitting vortex generators (VGs) on the blades of a constant RPM, pitch‐regulated, megawatt‐sized turbine suffering from surface roughness. Engineering modelling and experimental work were utilized, indicating that the degradation of energy production may be mitigated by the VGs. The modelling results indicated that the optimal configuration of VGs to maximize the annual energy production (AEP) depends on the degree of severity of surface roughness. Depending on blade surface condition and turbine characteristics, installation of VGs on an incorrect blade span or installation of too large VGs too far out on the blade may cause loss in the AEP. Therefore, engineering modelling is necessary before VGs may be retrofitted on a specific turbine. The modelling results indicated that the worse blade surface, the more gain may be obtained from the VGs. The work included a full‐scale experimental validation of the present engineering model, lasting 27 months and comprising six turbines where VGs were mounted on three, each with a neighboring turbine as a reference. The turbines were analyzed in pairs, and the influence of the VGs was judged upon the relative difference in energy production before and after the installation. The reason was to limit measurement uncertainty. The results showed that all three turbines increased their energy production after the installation. Results from the three pairs showed an average increase in the energy production of 3.3%, being satisfactorily close to the average 2.8% predicted by the present engineering tool.     

Experimental parameter study for passive vortex generators on a 30% thick airfoil

Passive vane–type vortex generators (VGs) are commonly used on wind turbine blades to mitigate the effects of flow separation. However, significant uncertainty surrounds VG design guidelines. Understanding the influence of VG parameters on airfoil performance requires a systematic approach targeting wind energy‐specific airfoils. Thus, the 30%‐thick DU97‐W‐300 airfoil was equipped with numerous VG designs, and its performance was evaluated in the Delft University Low Turbulence Wind Tunnel at a chord‐based Reynolds number of 2×10⁶. Oil‐flow visualizations confirmed the suppression of separation as a result of the vortex‐induced mixing. Further investigation of the oil streaks demonstrated a method to determine the vortex strength. The airfoil performance sensitivity to 41 different VG designs was explored by analysing model and wake pressures. The chordwise positioning, array configuration, and vane height were of prime importance. The sensitivity to vane length, inclination angle, vane shape, and array packing density proved secondary. The VGs were also able to delay stall with simulated airfoil surface roughness. The use of the VG mounting strip was detrimental to the airfoil's performance, highlighting the aerodynamic cost of the commonly used mounting technique. Time‐averaged pressure distributions and the lift standard deviation revealed that the presence of VGs increases load fluctuations in the stalling regime, compared with the uncontrolled case.     

水泵水轮机转轮加装短叶片前后的流动特性对比

为对比高水头水泵水轮机的转轮加装短叶片前后的能量特性及流动特性,基于SST湍流模型,选取4个具有代表性的水泵及水轮机工况,对有/无短叶片的水泵水轮机进行全流道三维定常计算。数值模拟结果表明,以水泵运行时加装短叶片可抑制脱流与漩涡等二次流现象,降低单个叶片承受的水力载荷,提高转轮进出口、导叶区及蜗壳静压,使泵获得更高的扬程。水轮机运行时添加短叶片可减小转轮出口环量,改善在尾水管内形成的复杂漩涡流,提高其水力效率。相同边界条件下,长短叶片转轮改善了转轮区的流动条件,从而提升了机组的能量特性及水力稳定性。