Computational Fluid Dynamics Optimization of Hybrid Savonius–Darrieus Hydrokinetic Turbine Efficiency and Self-Starting Performance Using Design of Experiments

In this study, statistical analysis and computational fluid dynamics (CFD) were employed to study the efficiency and self-starting trade-off of a Savonius–Darrieus hybrid turbine. The research focused on identifying the optimal radius ratio, coupling angle, tip–speed ratio and azimuth angle to maximize static moment. CFD simulations were conducted in ANSYS 2024 R1 to calculate the static moment for each configuration. These results were analyzed to determine the standardized effects, main effects, and variance, identifying the impact of each variable on performance. Following the statistical analysis, five regression models were proposed to predict self-starting capability, with the fifth model (ms5) demonstrating the highest goodness-of-fit. This model was optimized using a response volume visualization, where the study variables were mapped against a static moment color gradient. Iteration of the ms5 model revealed that an optimal arrangement of 0.8 (radius ratio), 102° (coupling angle), and 45° (azimuth angle) yielded a static moment of 173.59 Nm, surpassing all initial DOE results. A comparative analysis showed that the standalone Darrieus and Savonius static moments were 93.18% and 26.74% lower, respectively, than the optimized hybrid value. The reported static moment characterizes the rotor’s tendency to initiate rotation from rest; it does not constitute a dynamic start-up simulation. Furthermore, the integrated self-starting and efficiency model allowed the identification of a balanced configuration between efficiency and static moment, consisting of a radius ratio of 0.37, a coupling angle of 104°, a TSR of 2.2, and an azimuthal angle of 43°. This case was numerically simulated to verify its performance, resulting in an efficiency of 48.97% and a static moment of 35.46 Nm, respectively.