Power performance and flow structure analysis of a deflector-augmented savonius hydrokinetic turbine under variable flow speeds

A Savonius hydrokinetic turbine (HKT) experiences variations in water flow speed due to seasonal changes, impacting the turbine's performance. These fluctuations may also affect the performance of deflector-augmented turbines and their optimal deflector configurations. This study aims to elucidate the effects of flow speed variation on the performance of a deflector-augmented Savonius turbine for various deflector angle and deflector position configurations. A wind tunnel experiment was conducted at equivalent airflow speeds ranging from 4.4 m/s to 7.0 m/s, parameterized in terms of Reynolds numbers between 9.27 10⁴ to 1.48 10⁵. Results showed that increasing flow speed raised the maximum coefficient of powerC_Pmax of the turbine, which occurred at a higher tip speed ratio, λ. However, the optimal deflector configurations remained unaffected, as the flow structures in the deflector-turbine region were greatly affected by the deflector configurations instead of the flow speed variation. As a result, the turbine achieved optimal performance with the same deflector configurations across all flow speeds. This finding suggest that the deflector-augmented Savonius HKT can be effectively deployed operating sites with varying flow speeds without requiring a complex deflector configuration controller.