This study explores the impact of various geometric modifications, including leading-edge openings, trailing- edge openings, and circular openings, on the performance of the H Darrieus hydrokinetic turbine. These modifications involved the removal of material from a symmetrical NACA0018 airfoil along its surface. The leading edge and trailing edge openings extended from the lower to the upper surface of the blade, while the circular opening was applied exclusively to the upper surface. Using the commercial software ANSYS® V22.2, the turbine was designed, discretized, and analyzed through computational fluid dynamics employing the Realizable K-e turbulence model. The primary output variable measured was torque, from which the power coefficient for each design modification was derived, allowing for the calculation of efficiency in each scenario. Notably, the configuration featuring the upper circular opening achieved the highest efficiency at 51.88% at a Tip Speed Ratio (TSR) of 2.0, a significant improvement over the standard case which had an efficiency of 45.16%. In contrast, the leading-edge and trailing-edge openings resulted in reduced efficiencies of 44.54% and 31.19%, respectively. The enhanced power coefficient of the H Darrieus hydrokinetic turbine with circular openings is attributed to the increased pressure difference generated between the upper and lower surfaces of the blade, surpassing the performance of the standard design.

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.