Hydrodynamic Effect of Highly Skewed Horizontal-Axis Tidal Turbine (HATT) Rotors

While hydro turbines generate over 40% of the world’s total renewable energy, these traditional turbines present a great environmental concern due to the potential of their sharp blades to damage aquatic lives and ecology, along with their harmful noise and vibration during operation. One effective solution to these environmental issues is to substantially increase the skew of these blades, which would result in a much safer blade operation for aquatic animals (such as fish, etc.) and a substantial reduction in noise and vibration. Adding skew to turbine rotors is known to reduce cavitation and noise, and hence, to mitigate the environmental impact on underwater fauna and flora. However, adding skew will compromise the power performance of the turbines. This study aimed to identify the effect of rotor skew on the hydrodynamic power performance of a series of horizontal-axis turbine rotors that were manufactured using 3D printing technology and tested in a towing tank. The diameter of the turbine rotor model was 0.3 m and the skewed angle contained positive and negative angles of 45, 60 and 90 degrees along with a non-skewed rotor. This study was conducted to analyze the hydrodynamics of a turbine rotor with different skew angles and a 0-degree skewed rotor. Various tip speed ratios, ranging from 2.3 to 4.3, were set in accordance with the RPM and the carriage speed. Gain and filter were applied to boost the signal, and post-calibration was conducted. The results show that (1) the non-skewed rotor had the highest power coefficient; (2) the rotor with a skew angle of 45 degrees had the lowest power loss, at 6.97%, compared with the zero-skew rotor blades; (3) while the larger the skew, the more loss in power production efficiency, the rotor with a negative 90-degree skewed angle had the largest power loss, 31.42%. It was then concluded that, based on the results and analysis, (1) to achieve the greatest reduction in noise and vibration, the rotor with a skew angle of 90 degrees would be the best choice, and (2) to mitigate noise/vibration and efficiency due to skew, the rotor with a skewed angle of 45 degrees would be the best design choice.