Performance prediction and fundamental understanding of small scale vertical axis wind turbine with variable amplitude blade pitching

Abstract

This paper predicts and analyzes the aerodynamic performance of a Vertical Axis Wind Turbine (VAWT) with variable amplitude dynamic blade pitching. This study contributes to the physics based understanding of the dependence of power extracted by the turbine on various design parameters. An aerodynamic model based on double multiple streamtube theory coupled to an airfoil table lookup based blade element theory analysis and attached unsteady aerodynamics is used for performance prediction. A method for calculating virtual camber effect for dynamically pitching blades is proposed and validated. Inclusion of dynamic virtual camber effect and unsteady aerodynamics are critical for accurate performance prediction. The parametric study relates performance of VAWT to rotor solidity, blade airfoil and pitch amplitude. It is concluded that the amplitude of sinusoidal blade pitching must be varied with wind speed and tip speed ratio to maximize the power extracted from the turbine for wide range of wind speeds and tip speed ratios. High (about 35°) pitch amplitudes work best for tip speed ratios below 0.5 and the pitch amplitude should be reduced to approximately 10° for tip speed ratios greater than 2.0.