Numerical Investigation of Rotor Aspect Ratio Effects on an Augmented Drag-Based Hydrokinetic Turbine Performance

Hydropower is a crucial renewable energy source in achieving energy transition goals. Conventional dam-based hydropower plants cause environmental degradation, social displacement, and high costs. Hydrokinetic turbines (HKTs) present a sustainable alternative, but their efficiency remains a challenge. Rotor aspect ratio (AR) is defined as the ratio of rotor length to rotor diameter. It influences the torque and power coefficients of HKTs. This study investigates the effects of AR on an augmented drag-based Savonius HKT through numerical simulations. Five AR configurations (0.5 to 1.5) are analyzed by solving Unsteady Reynolds-Averaged Navier-Stokes (URANS) equations with the k-ω SST turbulence model. Results show that AR 1.0, with a rotor diameter and length of 1.23 m, achieves the highest power coefficient (Cp = 0.525) at Tip Speed Ratio (TSR) of 1.002, improving efficiency by 20% compared to previous studies. The findings suggest that increasing AR enhances peak Cp while optimizing swept areas and drag forces. These findings provide insights for optimizing HKT designs to enhance energy capture and feasibility in slow-moving water environments.