Optimization of fish-friendly bulb turbine based on orthogonal method and computational fluid dynamics

Abstract

A high-performance, fish-friendly bulb turbine was developed in this study by optimizing a runner with spiral blades to enhance the flow passage for fish. The key aspect of this work is multi-objective optimization based on the orthogonal method. Four factors were focused on: the number of guide vanes, the wedge angle of the blades, the distance of vaneless space, and the pitch variation ratio. The optimal value of each design parameter was determined through comprehensive measurements, including intuitive analysis, range analysis, and synthetical frequency analysis. The evaluating indexes were unit output, efficiency, fish-passing damage rate, pressure fluctuation, maximum blade deformation, and equivalent stress. The results indicate that the pitch ratio parameter significantly affected hydraulic performance, while the number of guide vanes primarily influenced fish-passing performance. The optimized turbine achieved a hydraulic efficiency of 84.05%, with a fish damage rate of only 0.01%. Structurally, the vibration modes of the runner were mainly oscillating deformation, rotating deformation around the axis, and bending deformation. The difference between the hydraulic excitation frequencies and the natural frequencies of the runner exceeded 20%, ensuring no resonance under the best efficiency point (BEP) condition. The dry and the prestressed modals showed similar natural frequencies and vibration patterns for the runner, whereas the wet modal showed higher natural frequencies for the runner.