In-pipe drag-based turbine blade optimization for energy harvesting in urban water networks: A novel theoretical approach

Recent urbanization trends, along with economic and population growth, have led to increasing global energy demand. In response, in-pipe turbines have gained attention for harnessing hydrokinetic energy from urban water pipelines. Among the various turbine models, vertical-axis drag-based turbines are prevalent in plants with small-diameter pipelines. However, despite recent efforts to identify optimal design of these turbines, the optimization process remains challenging due to the numerous blade profile parameters involved. Accordingly, this paper focuses on introducing a fast and reliable blade shape optimization approach. Firstly, a parametric modeling method is introduced to create different blade geometries. Following this, a theoretical method was developed to calculate the turbine torque coefficient. The reliability of this method was assessed by comparing its results with numerical simulations. The accuracy of the numerical simulations was further validated through experimental tests, revealing a maximum deviation of 6.4 %. Subsequently, a multi-objective optimization technique (NSGA-II) is employed to maximize the turbine's output torque, with the turbine's geometrical features serving as constrains. As a result, the numerical simulations indicated that the proposed design achieved a 40 % increase in torque coefficient and a 38 % improvement in efficiency compared to the conventional model in the bounds of the practical rotational speeds.