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 (Rsa = 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 (cp) and torque (ct) coefficients across varying attachment angles and ratios of swept area. Performance was evaluated using the curves of cp and ct versus tip-speed ratio (λ), along with velocity contour plots. Results showed that the SDHKT with DHKT#1 at φ = 0° achieved the highest cp = 0.0936 at λ = 1. The φ = 30° model slightly outperformed in ct. Larger Rsa values enhanced cp and ct at lower λ (< 0.9), while smaller Rsa values were better at higher λ (> 0.9). The optimal configuration is SDHKT1 with φ = 0° for low λ performance, combined with larger Rsa for improved efficiency at high λ. Optimizing rotor speed and blade design is essential to reduce flow blockage and improve real-world performance.

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