Moment of Inertia Dependence of Vertical Axis Wind Turbines in Pulsating Winds

Vertical Axis Wind Turbines (VAWTs) are unaffected by changes in wind direction, and they have a simple structure and the potential for high efficiency due to their lift driving force. However, VAWTs are affected by changes in wind speed, owing to effects originating from the moment of inertia. In this study, changes in the rotational speed of a small VAWT in pulsating wind, generated by an unsteady wind tunnel, are investigated by varying the wind cycle and amplitude parameters. It is shown that the responses observed experimentally agree with simulations based on torque characteristics obtained under steady rotational conditions. Additionally, a simple equation expressing the relationship between the rotational change width and amplitude of the pulsating wind is presented. The energy efficiency in a pulsating wind remains constant with changes in both the moment of inertia and the wind cycle; however, the energy efficiency decreases when the wind amplitude is large. 1. Introduction Vertical Axis Wind Turbines (VAWTs) [1] are promising energy devices [2–4]. They have a simple structure, their output power is unaffected by changes in wind direction, and based on their lift driving force, they have the potential for high efficiency. However, VAWTs are affected by wind speed variation, owing to their moment of inertia. As a result, rotor response to wind speed variation is important when considering the proper control of VAWTs. In general, for the design, analysis, and control of the more widely prevailing Horizontal Axis Wind Turbines (HAWTs), prediction of unsteady aerodynamic loads is challenging and crucial. For this reason, much effort has been put into modeling the unsteady aerodynamics of wind turbines [5]. In the case of VAWTs, even if the wind speed is constant, the angle of attack of the inflow to a blade periodically changes during rotation. Thus, dynamic analysis of a VAWT is essential for reliable design and reduction of cost [6]. In practice, the problems are even more complex, as the wind turbines are often installed under conditions of turbulence and abrupt wind-speed variations. Ordinarily, wind turbine performance predictions are compared with field or experimental data measured under constant wind speed. Recently, transient responses were measured for a straight-bladed VAWT subjected to steplike wind speed variation in an unsteady wind tunnel [7]. In the present study, to investigate the dependence of VAWT performance on the moment of inertia in unsteady wind, the response of a straight-bladed VAWT to a pulsating wind is measured,