冲击式水轮机水斗设计方法及性能优化

Bucket design method and performance optimization of a Pelton turbine

雅鲁藏布江下游蕴藏着丰富的水电资源,具有高水头、大容量等特点,冲击式水轮机是优选机型。转轮是冲击式水轮机的核心过流部件和做功部件,水斗形状对转轮性能至关重要。该文将水斗三维几何形状的构造线划分为轮廓线、过流剖面线和引导线3类,给定若干特征参数,提出了一种可控参数的冲击式水轮机水斗三维设计方法。选择水斗深度、宽度增量、出水边角度、分水刃角度和缺口圆直径等参数对冲击式水轮机水斗开展正交优化。由极差分析可知,宽度增量对转轮效率的影响最大,对出水边角度、缺口圆直径和水斗深度的影响较小,对分水刃角度的影响最小。优化后,冲击式水轮机的水力效率增加了6.71%。相比于原型水斗,优化水斗的总扭矩更大,在扭矩减少至0的过程中平缓过渡,有利于提高机组的水力效率和运行稳定性。

[Objective]The Yarlung Zangbo River contains numerous hydropower resources,with high head and large flow rates in the downstream region,which is conducive to power generation by Pelton turbines.Pelton turbines convert the kinetic energy generated from the water potential energy into mechanical energy for rotating a runner.The runner is the core component for the flow and work of the Pelton turbine,and the shape of its bucket is crucial for the runner's performance,which is uniformly arranged along the hub of the runner.As the surface shape of the bucket is complex,several parameters are required to determine its geometry model,undoubtedly posing a huge obstacle to work.In this paper,a design method is proposed to address the problem of designing and improving the bucket based on the Bézier curve.The design space is simplified as much as possible based on geometry,and the Bézier curves are utilized for designing the bucket shape.An orthogonal analysis is applied for the optimization of bucket parameters,while the computational fluid dynamics method is employed for analyzing the energy characteristics and three-dimensional flow field of the Pelton turbine.In the bucket design method,the three-dimensional geometry of the bucket can be divided into contour,flow profile,and guidelines,and several characteristic parameters can be determined for those lines.Each type of line includes several biquadratic Bézier curve connections.The number of characteristic line parameters is decreased by establishing a connection between five control points of the Bézier curves.Thus,a three-dimensional design method for the bucket of the Pelton turbine is proposed based on the five controlled characteristic parameters.The main optimization parameters are chosen by the geometry.Subsequently,bucket depth,width increment,outflow angle,splitter angle,and cutout diameter are chosen to conduct orthogonal optimization for the Pelton turbine bucket.For further analysis of the flow characteristics of the optimized bucket,the runner is modeled based on the optimum parameters.In the computational fluid dynamics method,grids are meshed by ICEM,and computational fluid dynamics is performed with ANSYS FLUENT.The results of the polar analysis and three-dimensional unsteady flow field revealed that width had the maximum influence on runner efficiency;outflow angle,cutout diameter,and bucket depth had a smaller influence;and splitting angle had the minimum influence.After optimization,the hydraulic efficiency of the Pelton turbine was increased by 6.71%.The optimized bucket demonstrated a larger torque peak than the prototype bucket.The bucket always showed large torque when its torque decreased to zero and exhibited smoother curve transition and longer work time.Thus,the optimized bucket demonstrated greater total torque than the prototype bucket;furthermore,the former's high-pressure area was larger,making the energy conversion of water from the nozzle to the bucket more effective.This paper proposes a three-dimensional design method for the Pelton turbine bucket based on the controlled characteristic parameters.The energy performance of the Pelton turbine was enhanced by the orthogonal optimization and three-dimensional flow simulation.