Synergistic Effect of J-Shape Airfoil on the Performance of Darrieus-Type Straight-Bladed Vertical Axis Wind Turbine

Abstract

Darrieus-type straight-bladed vertical axis wind turbines (SB-VAWTs) are more appropriate for generating electricity than other VAWTs mostly suitable for regions having low to medium wind speed. The installation of SB-VAWTs faces start-up problems, which limits its applicability in low-wind speed environments. The start-up problem arises mainly due to the cross-sectional blade profile of the SB-VAWTs and is the crucial parameter used for blade design. To overcome this issue, the present investigation aims to study the influence of the J-shape airfoil with various opening ratios in the Darrieus-type SB-VAWTs in terms of starting torque and aerodynamic performance. The design of a J-shape airfoil is created by removing a portion toward the trailing edge of the conventional NACA 4415 airfoil on its upper or lower surface. This analysis displays a maximum power coefficient of 0.517, 0.512, 0.506, 0.498, and 0.488 when the Darrieus-type SB-VAWT utilizes upper cut J-shape airfoils with opening ratios of 0.8, 0.7, 0.6, 0.5, and 0.4, respectively, at the tip speed ratio (TSR) of 1.6. These values are higher than the power coefficient (0.486) of conventional NACA 4415 airfoil at the same TSR. The SB-VAWT depicts a lower performance while it employs the lower cut J-shape airfoils. Furthermore, the present study demonstrates that the power and torque coefficient of SB-VAWT improves by about 31% when the opening ratio of upper cut J-shape airfoil is varied from 0.1 to 0.8.