An experimental study to investigate the effect of pitch angle and wave characteristics on the performance of a horizontal axis tidal turbine

Abstract

This study investigates the performance characteristics of a scaled-down three-bladed tidal turbine in a towing tank. The effects of pitch angle, electrical load, wave characteristics, and current velocity on turbine performance are examined. The experimental model, a 1:6 scale horizontal-axis tidal turbine with a rotor diameter of 1.15 m, is tested in the Strait of Khoran in Iran, selected based on tidal potential evaluation. After calibration and uncertainty analysis, experimental tests are conducted using the Taguchi method to optimize parameters and explore turbine performance in different conditions: current-only and wave-current interactions. Results demonstrate the direct relationship between power, momentum, thrust, rotor speed, and current velocity. Notably, power and momentum coefficients exhibit nonlinear (polynomial) variations at different tip speed ratios (TSRs). The presence of waves consistently enhances turbine performance compared to the no-wave mode, albeit with a lesser impact than other variable parameters. A pitch angle of 18.77° in the presence of waves yields a significant increase of up to 31.1% in power coefficient and up to 23.6% in momentum coefficient, compared to the no-wave mode. The optimal blade angle generally falls within the range of 30–35 mm, with 35 mm (18.77°) and 30 mm (22.72°) as the respective optimum pitch angles for wave-current interaction and the no-wave state. Optimal electrical load is achieved by setting Rheostat equal to 20 Ω, resulting in a remarkable 11% to 40% increase in system efficiency. In the upstream flow, the maximum power and momentum coefficients are observed as 0.219 and 0.033, respectively, at a TSR of 6.62 in the presence of waves with a dimensionless wave number of 3.43. Similarly, in the no-wave mode, the optimal power and momentum coefficients are obtained as 0.205 and 0.0286, respectively, at a TSR of 7.18. These findings highlight the significance of waves with a dimensionless wave number of 3.43.