康达效应对冲击式水轮机影响研究

Study on Influences of Coanda Effect in Pelton Turbine

为了研究康达效应对冲击式水轮机水力性能的影响,以某六喷嘴立式冲击式水轮机为基础,经相似换算模型机尺寸,通过ANSYS CFX流体仿真软件分析得到水轮机内部流场的特性和单个水斗一个射流周期的扭矩变化曲线。结果表明:在特定运行工况下,水轮机速度比减小,水斗对射流的吸附程度减弱,射流扭曲变形状态减弱、集束性提高;基准水斗基圆半径减小,射流扭曲变形减弱,在高扭矩区域水斗扭矩值增加;水斗切水边背面夹角增加,水斗背面对射流的挤压作用加剧,引起水斗背面负压区域面积增加,射流流经下一个水斗正面位置更靠近水斗根部。计算转轮水力效率时,为降低扭矩波动引起的误差取一个旋转周期内平均扭矩与喷嘴出口射流能量的比值计算。研究所得成果为冲击式转轮设计、运行管理提供参考。

In order to study the influences of Coanda effect on hydraulic performance of Pelton turbine,the six-nozzle vertical Pelton turbine is taken as the study object,and then the size of model machine is converted by similarity,the characteristics of flow field in turbine and the torque curve of a single bucket during one jet cycle are obtained through the analysis of ANSYS CFX fluid simulation software.The result shows that under certain operating conditions of the turbine speed ratio decreases,the absorption degree of the bucket to the jet weakens,the distortion and deformation state of the jet weakens,and the cluster property improves;when the base circle radius of the reference bucket decreases,the jet distortion is weakened,and the torque value of the bucket increases in the high torque region;when the angle on the back of the cut edge of the bucket is increased,the squeezing effect on the jet is intensified,causing the negative pressure area on the back of bucket is increased,the jet flow through the next bucket's front position is closer to the bucket root.In order to reduce the error caused by torque fluctuation,the ratio of the average torque within a rotating cycle to the jet energy at the nozzle outlet is calculated when calculating the runner's hydraulic efficiency.The study results can provide references for design and operation management of Pelton turbine runner.