Multi-Objective Optimization of an Undershot Cross-Flow Water Turbine Operating in a Free Surface Flow Field

In this study, design of experiment, three-dimensional free surface flow analysis, response surface method, and the multi-objective optimization method were combined to develop a multi-objective optimization design method for an undershot cross-flow water turbine. This design method was applied to a water turbine runner, and multi-objective optimization was performed to achieve low head and high power output. The resulting optimized runner was tested, and the flow field around the runner and the torque fluctuation acting on the blade were investigated. The results showed that the effective head of the optimized runner was 20.2% higher than that of the original runner, but the turbine output was significantly higher (98.3%). This is because, although the optimized runner had fewer blades, the torque of each blade increased significantly, since the optimized runner had a narrower negative torque range and a larger positive torque range than the original runner in terms of the torque fluctuation of one blade during one runner rotation, resulting in a significant increase in total torque.