Analysis and design of a new updraft free-exit-flow low-head hydropower turbine system
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A new updraft free-exit-flow low-head hydropower turbine system is designed to enhance tailrace water quality, to minimize fish mortality in turbine flow passage, to improve turbine mechanical performance, and to reduce costs and time of hydropower development. This study applies the theoretical, experimental, and computational approaches to analyze the characteristics of this turbine and to develop improved methods for designing the turbine system components.;The theoretical component of this study contains the flow analysis for the new turbine based on the fundamental principles of fluid dynamics. It analyzes important aspects of turbine flow characteristics such as anti-gravitational flow, spiral flow, helical flow, energy conversion, meridional flow, inflow velocity moment distribution, and variation of velocity moment in the turbine runner. The analysis leads to the proposal of a set of principles, criteria, and methods for hydraulic design of the new turbine. They include mainly an approach for designing the divergent runner chamber and a two-dimensional method for hydraulic design of runner blades. These methods are applied to design a new sample prototype turbine.;Pilot turbine experiments and computational flow analyses are also conducted to investigate the performance and to evaluate and optimize the turbine design. The experiments give encouraging results on the turbine efficiency. They also intuitively demonstrate the new turbine's capability of improving downstream water quality. The experimental results are used to confirm creditability of the numerical models. The numerical flow computations provide detailed flow information in flow passage of both the pilot turbine and the sample prototype turbine. Turbine hydraulic efficiency is estimated based on the computational results. The numerical flow analysis approach is also used to extend the turbine performance curves obtained in the experiment, to identify the initial pilot turbine design insufficiency, and to predict the turbine efficiency under optimal inflow conditions. The flow analyses for the sample prototype turbine evaluate the validity of the proposed design methods for the new turbine. They also identify the potential areas of design improvement for the sample turbine. Initial design optimizations are performed. The improved sample prototype turbine can reach a hydraulic efficiency of 82.2%. The flow patterns in the improved sample turbine are presented. Fish paths in the turbine flow passage are illustrated.