CFD investigation on the combined configurations between a 2-stage Savonius and the twisted delta-shaped-bladed Darrieus hydrokinetic turbines

A combined Savonius–Darrieus hydrokinetic turbine ( SDHKT ) was studied to leverage the strengths and mitigate the weaknesses of each turbine type. The design used a 2-stage Savonius (SHKT) and 2-bent delta-bladed Darrieus turbines (DHKT) with constant and reduced cross-sections. ANSYS Fluent, with the SST k - ω turbulence model and sliding mesh technique, was used to simulate various configurations, focusing on attachment angles ( φ = 0°, 20°, 30°, 90°, 120°) and ratios of swept area ( R sa = 0.4, 0.3, 0.2). the computational simulations of the combined SDHKT models yield reliable results, with a deviation of only 1.5% from the published experimental data. The validation of the CFD approach confirmed its accuracy in predicting turbine performance, including power ( c p ) and torque ( c t ) coefficients across varying attachment angles and ratios of swept area. Performance was evaluated using the curves of c p and c t versus tip-speed ratio ( λ ), along with velocity contour plots. Results showed that the SDHKT with DHKT#1 at φ = 0° achieved the highest c p = 0.0936 at λ = 1. The φ = 30° model slightly outperformed in c t . Larger R sa values enhanced c p and c t at lower λ (< 0.9), while smaller R sa values were better at higher λ (> 0.9). The optimal configuration is SDHKT1 with φ = 0° for low λ performance, combined with larger R sa for improved efficiency at high λ . Optimizing rotor speed and blade design is essential to reduce flow blockage and improve real-world performance.