Bucket design method and performance optimization of a Pelton turbine

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.