Effect of tip speed ratio on power coefficient of double savonius hydrokinetic water turbines

¹ Department of Mechanical Engineering, Faculty of Industrial Technology and Systems Engineering, Institut Teknologi Sepuluh Nopember, Kampus ITS Keputih Sukolilo, Surabaya 60111, Indonesia
² Department of Mechanical Engineering, Faculty of Engineering, Universitas Negeri Surabaya, Kampus Unesa 1, Jalan Kampus Unesa Ketintang, Surabaya 60231, Indonesia

^* Corresponding author: priyoheruadiwibowo@unesa.ac.id

Published online: 22 December 2025

Abstract

The growing global emphasis on sustainable development has increased demand for renewable energy sources. Hydrokinetic turbines have emerged as efficient and environmentally sustainable solutions for power generation in flowing water. The Savonius turbine is notable for its simple design, low maintenance requirements, and effective performance at low water velocities. This study examines the influence of Tip Speed Ratio (TSR) on the performance of a Savonius hydrokinetic turbine to identify optimal operating conditions. Numerical simulations were used to evaluate flow characteristics and performance metrics across a range of TSR values. The findings indicate that the power coefficient (Cp) attains its maximum at TSR = 1.0, corresponding to the highest energy conversion efficiency. Flow-contour analysis shows stable, symmetrical velocity and pressure distributions at this TSR, with well-formed vortices that produce maximum torque. The moment coefficient (Cm) decreases as TSR increases, reaching its highest value at low TSR (0.4–0.5). Therefore, TSR = 1.0 is determined to be the optimal operating point, balancing turbine efficiency and flow behavior, and offering practical guidance for the optimization of small-scale hydrokinetic energy systems.