混流式水轮机内部空化流动数值模拟

为探究不同比例的长短叶片对混流式水轮机内部流场空化特性的影响,基于欧拉-欧拉方法中均匀多相流假设的混合两相流体无滑移模型,采用RNG k~ε湍流模型以及三维时均N-S方程,对各混流式水轮机进行全流道三维定常空化湍流计算,获得了3种不同比例长短叶片对应的混流式水轮机在各空化系数下空泡相的流动特征以及各水轮机对应的σ~η曲线图。计算结果表明,当长短叶片比例为0.47时,水轮机临界空化系数最小,为0.060 8,相比长短叶片比例为0.6时降低了8.82%;当3种水轮机处于同一空化系数下时,该型水轮机效率最高;随着水轮机转轮短叶片的增多,水轮机的空化性能及能量性能得到了明显的提升。研究结果对长短叶片混流式水轮机的设计、优化和改型等具有一定的指导意义。     

混流式水轮机全流道三维定常湍流数值计算

基于标准k-ε双方程湍流模型和三维时均N-S方程,进行了混流式水轮机全流道的三维定常湍流计算.捕捉到了水轮机各过流部件内的流场和尾水管内的涡旋结构等流动信息.结果表明,水轮机的全流道CFD分析能够较为准确地预测出水轮机过流部件内的性能参数及内部流场结构,所得到的结果对进行水轮机的水力设计或改型优化设计等研究具有重要的指导意义.     

Transient simulation and analysis of the simultaneous load rejection process in pumped storage power stations using a 1-D-3-D coupling method

The load rejection imposes a danger in the pumped storage hydropower plants (PSPs),especially when two or more pump turbines reject their loads simultaneously.I...     

3-D simulation of transient flow patterns in a corridor-shaped air-cushion surge chamber based on computational fluid dynamics

The 3-D characteristics of the water-air flow patterns in a corridor-shaped air-cushion surge chamber during hydraulic transients need to be considered in the shape optimization. To verify the reliability of the water-air two-phase model, namely, the volume of fluid model, the process of charging water into a closed air chamber is successfully simulated. Using the model, the 3-D flow characteristics under the load rejection and acceptance conditions within the air-cushion surge chamber of a specific hydropower station are studied. The free surface waves, the flow patterns, and the pressure changes during the surge wave process are analyzed in detail. The longitudinal flow of water in the long corridor-shaped surge chamber is similar to the open channel flow with respect to the wave propagation, reflection and superposition characteristics. The lumped parameters of the 3-D numerical simulation agree with the results of a 1-D calculation of hydraulic transients in the whole water conveying system, which validates the 3-D method. The 3-D flow structures obtained can be applied to the shape optimization of the chamber.     

小型混流式水泵水轮机水力设计

采用二元理论结合螺旋势流设计了混流式水泵水轮机,并利用Pro/ENGINEER建立三维几何模型。通过对不同曲率导叶的CFD数值模拟计算,分别得到水泵工况和水轮机工况下的流场流线图、速度图以及压力图,证实标准导叶更适用于混流可逆式机组。效率估算结果显示,机组效率在水轮机工况达到85%,水泵工况达到88%,说明设计方法可行。     

混流式水轮机上冠空腔结构内部流场及单向流固耦合分析

为研究上冠空腔结构对混流式水轮机水力性能与结构特性的影响,建立了不含上冠空腔结构（No UpperCrown Cavity Structure,NUCCS）和含上冠空腔结构（Upper Crown Cavity Structure,UCCS）的两种混流式水轮机全流道几何模型,基于SST湍流模型、顺序耦合法、预应力模态分析,对NUCCS与UCCS的两种混流式水轮机展开数值模拟和单向瞬态流固耦合计算,发现泄水锥处上冠空腔结构可减少转轮内部二次流动损失。在0.8Q_d、Q_d和1.2Q_d的3种流量工况点,分别对混流式水轮机展开瞬态流固耦合计算,对比研究转轮结构的应力应变特性。研究发现含UCCS时,转轮等效应力和变形量均有减小。在小流量0.8Q_d工况点,转轮结构等效应力及应变较小,其最大变形点位于下环附近。在设计流量Q_d和大流量1.2Q_d工况点,转轮等效应力及应变较大,其最大变形点位于上冠附近。在NUCCS与UCCS的转轮进行预应力模态分析时,发现上冠空腔结构对转轮的模态影响很小。本文研究内容可为提升混流式水轮机设计水平提供一定参考依据。     

偏工况下混流式水轮机压力脉动数值仿真及其改善措施研究

某电站混流式水轮机组在部分负荷时机组出力大幅摆动,真机试验结果显示尾水管涡带频率与发电机低频振荡频率接近,二者产生共振导致功率波动。本文采用CFD方法对该电站混流式水轮机进行了三维非定常数值模拟,对包括电站现用泄水锥、加长型泄水锥、在尾水管内安装阻尼栅、在尾水管内安装导流板等4种方案下水轮机内部非定常流动进行了仿真,对比分析了各种方案对尾水管内涡带形状和压力脉动的影响。计算结果表明:加长泄水锥能降低压力脉动的幅值,但不能改变压力脉动频率;相比于阻尼栅,在尾水管中安装导流板能更有效地改变尾水管水压力脉动的主频并减小压力脉动的幅值,且对水轮机效率的影响较小。     

三峡水轮机全流道三维流动数值模拟研究

本文使用商业CFD软件FLUENT,开发了部分接口程序,进行了全流道原型水轮机三维湍流数值模拟研究,计算对象是中国水利水电科学研究院机电研究所为三峡右岸开发的水轮机模型,该水力模型有完整的模型试验资料,可用于检验计算结果。水轮机全流道三维湍流数值模拟,计算区域为包括蜗壳、固定导叶、活动导叶、转轮和尾水管的全部流道。模拟中控制方程采用了三维时均N—S方程、湍流模型采用两方程RNG k-ε模型,数值方法采用贴体坐标的有限体积法。共进行了3个开度条件下的计算,每个开度各进行4个典型工况的三维湍流流场模拟,通过数值方法求解控制方程,获得了全流道的流速和压力分布。计算结果表明流速和压力分布合理,数值计算得到的效率与试验得到的效率进行比较,结果吻合良好。     

有压管道充水过程水力特性三维数值模拟

运用Fluent软件建立三维模型,对某调水工程中的一段有压管道充水过程的水力特性进行三维数值模拟计算,采用PISO算法分析了管道充水过程中气体压力、水力要素及两相流流态变化情况。结果表明:充水流量的大小会导致管内气体压力的强烈变化;气体压力变化又会影响进口流速。在水体流到管道后部管壁之前,流线均匀,流态较好;之后气液两相彼此相间,流线错综复杂,流态紊乱,湍流能量较强。建议以"小流量充水原则"对类似输水管道进行试充水操作。     

轴流式水轮机模型飞逸过程三维湍流数值模拟

通过作者建立的非稳态过程三维湍流数值模拟方法,模拟了轴流式水轮机模型飞逸过程,并进行了其三维数值湍流计算,获得了机组到达最大转速时所需时间、最大飞逸转速值、飞逸过程内特性流场演变规律以及转速、流量、力矩与测点静压随时间变化的曲线。计算结果表明,所得最大飞逸转速与试验值非常接近,误差在1.5%以内;所得力矩及流量等外特性参数变化过程均符合高比转速水轮机理论特性;当转速增大到某一数值之后,尾水管水力稳定性急剧恶化是引起机组振动的主因。     

淹没紊动射流三维流场特性的数值模拟

采用RNGk-ε紊流模型对有限空间的单孔、双孔紊动射流的流场进行了三维数值模拟研究。研究结果表明:无论入流条件如何变化,经无量纲处理后的轴线流速分布曲线几乎都落在同一条无量纲速度分布曲线上,说明流动存在相似性。双孔射流时,流场存在分区结构,在不同的喷嘴间距下,射流的卷吸程度不同,S/D越大,射流之间的卷吸掺混作用越弱。     

三维非定常湍流尾水管涡带数值模拟

采用全流道三维非定常流动数值模拟方法,研究了混流式水轮机在部分负荷工况运行时,尾水管涡带在尾水管内引起的压力脉动现象。计算工况为典型的部分负荷工况,单位转速为70.52r/min, 单位流量为0.679m3/s。计算结果表明在4个计算点都得到了涡带低频压力脉动：频率为0.333Hz, 是转频1.25Hz的1/3.75,相近工况（n11=71.25r/min,Q11=0.689m3/s）模型试验测得涡带频率为5.31Hz, 是转频18.62Hz的1/3.51,从涡带频率看计算结果与试验测量结果一致。研究成果表明数值模拟方法是可行的,可以在设计阶段预测尾水管内涡带压力脉动的特性。     

水轮机导叶含端面间隙的水动力学研究

本文基于N－S方程和标准κ-ε紊流模型，采用贴体坐标和结构化网格，用SIMPLE算法，对带有间隙导叶叶栅进行三维不可压定常粘性流动数值模拟。详细研究比较了导叶有无间隙两种情况下的水轮机导叶水动力学特性，揭示了水轮机导叶端面间隙流动的运动规律以及间隙流动对主流的影响，计算结果与实验吻合，从而为导叶及上下端面的磨蚀以及水轮机的水力稳定性提供理论依据。     

基于VOF方法的尾水隧洞过渡过程明满流水力特性研究

针对尾水隧洞结合导流隧洞布置时过渡过程中的明满流问题,采用VOF气液两相流模型对尾水系统的三维流场进行计算和分析.计算了尾水隧洞过渡过程中满流至明流和明流至满流两种典型工况,通过模型试验中尾水隧洞监测点的数据验证了数值模拟的可靠性和准确性.在此基础上,对明满流的水力特性进行了深入的分析和研究.结果表明:尾水隧洞发生明满...     

3-D Lagrangian-based investigations of the time-dependent cloud cavitating flows around a Clark-Y hydrofoil with special emphasis on shedding process analysis

In the present paper, the unsteady cavitating flow around a 3-D Clark-Y hydrofoil is numerically investigated with the filter-based density correction model(FBDCM), a turbulence model and the Zwart-Gerber-Belamri(ZGB) cavitation model. A reasonable agreement is obtained between the numerical and experimental results. To study the complex flow structures more straightforwardly, a 3-D Lagrangian technology is developed, which can provide the particle tracks and the 3-D Lagrangian coherent structures(LCSs). Combined with the traditional methods based on the Eulerian viewpoint, this technology is used to analyze the attached cavity evolution and the re-entrant jet behavior in detail. At stage I, the collapse of the previous shedding cavity and the growth of a new attached cavity, the significant influence of the collapse both on the suction and pressure sides are captured quite well by the 3-D LCSs, which is underestimated by the traditional methods like the iso-surface of Q-criteria. As a kind of special LCSs, the arching LCSs are observed in the wake, induced by the counter-rotating vortexes. At stage II, with the development of the re-entrant jet,the influence of the cavitation on the pressure side is still not negligible. And with this 3-D Lagrangian technology, the tracks of the re-entrant jet are visualized clearly, moving from the trailing edge to the leading edge. Finally, at stage Ⅲ, the re-entrant jet collides with the mainstream and finally induces the shedding. The cavitation evolution and the re-entrant jet movement in the whole cycle are well visualized with the 3-D Lagrangian technology. Moreover, the comparison between the LCSs obtained with 2-D and 3-D Lagrangian technologies indicates the advantages of the latter. It is demonstrated that the 3-D Lagrangian technology is a promising tool in the investigation of complex cavitating flows.     

用TVD显隐格式模拟一维溃坝洪水波的演进与反射

应用空气动力学中的TVD格式构造了用于溃坝水流计算的显隐格式，模拟瞬间全溃时洪水波的运动，给出了与分析解的比较及多种数值试验，结果表明这类格式精度高，稳定性好，不产生虚假的数值振荡，对溃坝涌波具有较强的捕捉能力。     

Simulation of subcritical flow pattern in 180° uniform and convergent open-channel bends using SSIIM 3-D model

In meandering rivers, the flow pattern is highly complex, with specific characteristics at bends that are not observed along straight paths. A numerical model can be effectively used to predict such flow fields. Since river bends are not uniform-some are divergent and others convergent-in this study, after the SSIIM 3-D model was calibrated using the result of measurements along a uniform 180° bend with a width of 0.6 m, a similar but convergent 180° bend, 0.6 m to 0.45 m wide, was simulated using the SSIIM...     

平面形状不规则高桩码头对河道流场影响的数值模拟研究

为对东江北干流中下游右岸一形状不规则桩基码头对河道流场影响进行数值模拟,本文在前人研究成果的基础上,建立平面二维数学模型模拟此码头对河道流场的影响。计算结果表明：码头建设后其局部水域流速变化较大,但对整个河道的影响并不大。     

丁坝群对弯道水力特性影响的数值模拟研究

弯道螺旋流是弯道水流的特点之一,弯道环流会造成凸岸发生淤积,凹岸遭受冲刷,对护岸工程非常不利。在弯道中布设丁坝可有效减弱弯道螺旋流强度,改善水流流态,保护岸坡稳定。采用RNGk-ε湍流模型,应用VOF法捕捉自由水面,采用半隐式SIMPLE算法求解速度与压力耦合方程组,模拟在60°弯道内布设丁坝群后弯道水流特性。研究表明:数值模拟的水位、流速和试验数值据吻合良好。弯道内设置丁坝群后,可有效改善凹岸区域的冲刷及凸岸的淤积,主河槽的水深增加,水面横比降减小,说明丁坝群的布置在稳定弯道水流,防止岸坡冲於方面有较好的效果。