Performance Evaluation of Open-flow Micro-hydro Turbines: High inclined Archimedes Screw Turbine and Conical shape Vortex Turbine

Abstract

The world energy sector has started changing in promising ways, with the widespread adoption of renewables and related technologies boding well for a sustainable future. In this energy transformation, hydropower plays a major role having both pros and cons. But micro-hydropower is identified as the most sustainable hydropower generation method since it offers many economic, social, and environmental advantages. As an ecofriendly power generation method, micro-hydropower plants have a minimum impact on wildlife and the environment. Further, they have low installation and maintenance costs over other large scale hydropower generation methods. Furthermore, micro-hydropower is considered as a solution to generate electricity in rural areas; where exists a hydro energy potential but is hard to access to the national grid distribution. On the other hand, micro-hydropower plants can utilize for the discharge water flows in urban cities, recovering the waste energy as an efficient sustainable source of power. This study is mainly focusing on the applicability of micro-hydropower plants for the discharge outflow from the fish industry in Busan, South Korea. Several applicable sites are then measured and estimated the suitable micro-hydro turbines for recover the waste energy. Archimedes Screw Turbine (AST) and Vortex Turbine (VT) were suggested to improve to install in those areas. Therefore, at the initial stage, these two turbines are designed and optimized using the CFD techniques. This thesis is mainly focusing on the new findings of AST and VT with the CFD flow analysis. AST is considered a relatively new technology with the number of AST sites located mostly in European countries. Hence, the development of AST technology is a vital issue to utilizing hydro energy all around the world. Presently, a lot of researchers focus on the theoretical design procedures for AST considering various losses. Some researchers conducted experimental testing for the screws, comparing reliable validity with Computational Fluid Dynamic (CFD) analysis. Almost all of them were lab testing scale models claiming an average of 80% efficiency for low inclined angles. In the case of a real site having a small inclination, the length of the screw is large enough to bend the screw and exceed the bearing’s limitation. Therefore, this research was conducted to analyze the flow field in a real site scaled AST with the maximum possible inclination of 45 degree. In addition, the design was done without the upper and lower reservoir as it was estimated as a run-of-river flow system. Based on recommendations by previous works, the current screw turbine was designed according to Chris Rorres, the optimum design for an Archimedes Screw that is optimized for the screw pump. The simulated real scaled AST result of the maximum efficiency was around 82% for the 5.2 m hydraulic head. The turbine’s outer diameter was estimated at 1.2m, suitable for a 0.23m3/s flow rate and 45-degree inclination. Many researchers claim above 80% efficiency for low inclined ASTs with reservoirs. Still, this CFD study claimed that even higher inclined ASTs could achieve 80% efficiency, having a small leakage gap and optimum screw pitch in run-of-river real-scale applications. The gravitational water vertex power is considered as an ultra-low head hydropower solution. In the vortex power plant, the guided channel and the basin structure are used to form a vortex, where the rotational energy from the water can be extracted through a turbine. Nowadays, many researchers are focusing on enhancing the performance of vortex power plants on the hand of vortex basin and turbine optimization. Many researchers claim that the conical-shaped basing with the guided channel, resulting in a strong vortex, other than the cylindrical-shaped basin. Therefore, this study focused on the computational fluid dynamic (CFD) analysis around the vortex turbine, which is suitable for conical basin structure. Ansys CFX was used to observe the flow field around five different blade profiles and justify the relationship between flow phenomena and turbine performance. Five different blades categories are simulated starting from basic straight blade profile to conical shaped, different height and vertical and horizontal curvature profile. At the final stage, the basin and the turbine were fine-tuned based on the prior parameters to perform 63% CFD efficiency. With the comparison of this development of vortex turbine blade profiles, this study was concluded with calming the highest efficiency of the conical shaped turbine with vertical curved blades installed in a conical vertex basin. At the end of the CFD analysis, Vortex Turbine was scale-down to experiment to validate the performance of the new design. Experiment and CFD simulation results show a good agreement in both performance curves and the flow behavior. Scaled-down vortex turbine yield 59% efficiency where the efficiency reduction occurs due to scaling effects. The scale-down experiment results showed 57% efficiency having fair deviations mainly because of the mechanical losses and practical issues. Therefore, the CFD simulations are reliable enough to predict the vortex turbine models with well matching between experiment and simulations. As the final aim of this research, two types of micro-hydro turbines (AST and VT) were optimized using the CFD, while one turbine (VT) was able to experiment. Hence micro-hydro turbines, especially Archimedes Screw and Vortex turbines identified as a suitable method to recover the waste energy from discharge water flows even in urban areas. Thus, the development of micro-hydro technology is essential as a sustainable and renewable source of energy providing benefits to all humankind and mother nature.