Effects of Trailing Edge Alterations on the Performance of a Small-Scale, Low-Solidity Tidal Turbine Blade Designed for Less Energetic Flows

Abstract

Computer simulations aid in the design of any device. However, physical testing is still needed to validate these simulations and problems may arise if fabrication limits are not incorporated. This study was undertaken to quantify the losses in a low-solidity turbine rotor designed for less energetic flow. The blade was tested at a scale of 1m resulting in a blade length of 219mm. A 0.5mm minimum thickness fabrication limit was worked with by shifting all the points of the upper surface of the blade sections by 0.5mm at the 219mm scale introducing a huge distortion in each of the blade sections. Lift and drag characteristics of the distorted aerofoil are obtained via ANSYS Fluent and served as the corrected inputs for the BEM characterisation. It was found that the BEM predicts a reduced performance similar to the physical testing although it still over predicts the performance of the turbine. However, there is an agreement on the trend of the simulated performance and the physical testing in addition to the reduction of the variation between the two. Additional aerofoil alterations are studied to inform on future experimental designs. It was then found that out of the altered cases, shifting the upper surface by the required minimum thickness resulted in the best approximation of the simulated performance. This is far from acceptable as the variation between the ideal computer simulated case is too large to just incorporate corrections. Thus, an analysis is carried out using a 400mm scaled blade, thereby decreasing the distortion on each blade section. The results of the analysis show good agreement with the ideal section and minimal reduction in performance at about 5% less than the ideal.