A Comparative Aerodynamic Analysis of NACA and NREL Aerofoils for Darrieus Turbines Using CFD

Abstract

The selection of the aerofoil plays a crucial role in achieving optimum power output, especially for the inherently low-efficient turbines, such as the Darrieus wind turbine. For this purpose, different aerofoils belonging to NACA and NREL families have been investigated in terms of the aerodynamic performance, comparatively. Although NREL aerofoils are mainly utilised for the Horizontal Axis Wind Turbines, in the present study, their effect on the Darrieus type Vertical Axis Wind Turbine has been examined. In this point of view, the influence of the various aerofoils and their thickness on the turbine performance in different operating ranges have been evaluated using Computational Fluid Dynamics (CFD). Furthermore, by considering the low and high tip speed ratios, the instantaneous blade torque coefficient, and the contours of the pressure coefficient for the selected aerofoils have been analysed to provide further understanding. The research findings show that the conventional aerofoils, such as NACA0015 and NACA0021, illustrate better power output at optimum and high tip speed ratios, while the NREL aerofoils, such as S814 and S825, are able to increase the torque generation at the relatively low tip speed ratio regions. Even though this situation makes the NREL aerofoil more desirable to design a self-starting Darrieus turbine, NREL aerofoils lost their advantages due to the higher efficiency loss at the higher tip speed ratios. In addition to this, the thicker aerofoils, such as NACA0021 and S814, yield more power output at the low tip speed ratio compared to their counterpart profiles as a result of the high pressure difference achieved between their suction and pressure sides.