Performance Assessment of Darrieus Turbine with Modified Trailing Edge Airfoil for Low Wind Speeds

Abstract

Darrieus wind turbines are simple lift based machines with exceptionally high efficiencies in terms of power coefficient compared to similar drag based vertical axis turbines. However, in low Reynolds numbers, a notable performance loss was reported. As a potential solution, truncated NACA 0018 airfoil (NACA 0018TC-39) has been introduced with baseline cavity modification to achieve better start-up characteristics and to enhance the low wind speed performance. The baseline cavity will provide an additional benefit of reverse drag at low TSR which is obligatory for low wind speed start-up. Numerical optimization has been carried out on the conceived airfoil NACA 0018TC-39 to find out the effective truncation percentage in terms of the chord. The numerical study has been extended to compare NACA 0018 and NACA 0018TC-39 airfoil for their aerodynamic performances in terms of lift, drag coefficients and separation characteristics. The NACA 0018TC-39 airfoil was incorporated within a non-swept straight bladed Darrieus turbine miniature to experimentally evaluate the performance in terms of dynamic power coefficient, dynamic torque coefficient and static torque coefficient and compared with conventional NACA 0018 airfoil at six different Reynolds numbers 178917, 193827, 208737, 223646, 238556 and 268376. The experimental contrast implied that NACA 0018TC-39 airfoil turbine yielded almost double power coefficients at low Reynolds number compared to conventional NACA 0018 airfoil without hampering its performance at higher Reynolds number.