Modeling and analysis of vertical axis turbine with pitch adjusted by an eccentric guide

Abstract

ABSTRACT This study addresses analytical modeling and the assessment of a vertical axis turbine (VAT) with blade pitch adjustment by an eccentric guide, which is focused on applications with low tip speed ratio (TSR ≤1.5), hence focused mainly on the drag principle. This study aims at investigating a new proposal of vertical axis turbines with movable blades that promote an increment of overall efficiency by reducing drag forces during the contrary motion to the flow direction. Based on this approach, drag forces are significantly reduced and a positive torque is generated by lift forces during the contrary motion to the incoming flow, which provides the performance improvement of VAT. This novel concept is solved analytically for blades with 17 distinct airfoil profiles, and a parametric analysis is performed by varying guide radius, blade length, pitch offset, and tip speed ratio. According to the results performed in this study for a single-blade system, the proposed concept presents a power coefficient of 2.87% regarding the airfoil profile LN118 with a tip speed ratio of 1.0. Similarly, the airfoil profile s1210 has also been a relatively high-power coefficient of 2.09%, but with a tip speed ratio of 0.225. Symmetrical airfoil profiles provided lower power coefficients in comparison with nonsymmetrical, presenting maximum power coefficient for tip speed ratio lower than 0.3. It is worth highlighting that the novel concept of blade pitch adjustment is feasible by a passive system based on a cam-follower mechanism.