Abstract
Wind energy has proved to be a promising sustainable energy source; the energy of wind has been harvested not only for decades but for centuries. It was in the late 19th century that wind energy was used to directly obtain electrical power. Horizontal axis wind turbines (HAWTs) are widely used in commercial applications but recently a lot of research is being done on vertical axis wind turbines (VAWTs) to improve their operation and efficiency. Absence of yaw mechanism, low noise emission, and low manufacturing, installation and maintenance costs are some of the prominent advantages of VAWT over HAWT. The objective of this study is to evaluate the performance of different blade airfoils and the influence of blade pitching in the operation of VAWT. Blade pitching is widely used in HAWTs and has proven to be very advantageous in terms of output power, but the effect of blade pitching on VAWT has not been widely studied and much less practically implied due to complex functional mechanism. VAWTs with fixed pitch experience continuously varying angle of attack which reduces the power generation. Airfoils tested in this study, for their performance on a VAWT rotor, are Joukowski airfoil (J-15), NACA0012 and NACA4312, furthermore, passive blade pitching was applied to analyze the effect of inoffset and out-offset blade pitching on the performance of the turbine. High fidelity Navier-Stokes computational flow models were applied for the analysis. A 2D unsteady CFD model was constructed to perform the simulations. Power and torque coefficients were evaluated over a varying range of tip speed ratios and a strong correlation of these coefficients was seen with different input parameters, such as airfoil shape, turbine solidity and tip speed ratios. Out-offset blade pitch angles showed better results than in-offset blade pitch angles.
