Role of the galloping force and moment of inertia of inclined square cylinders on the performance of hybrid galloping energy harvesters

Energy harvesting by a square cross-section cylinder, inclined at different angles from the incoming wind flow, prone to galloping oscillations is investigated. The cylinder is fixed at the tip of a cantilever beam at a definite angle, to which is attached a piezoelectric layer and a permanent magnet placed in the close vicinity of a coil. Existing aerodynamic-coefficient experimental values as a function of the incident angle of attack are utilized for determining the aerodynamic force on each inclined cylinder. Seven-order polynomial is recognized to be a convenient choice for performing the analyses in this study. After establishing the galloping aerodynamic force of each case, a reduced-order model is developed for the beam-cylinder energy harvester using Galerkin discretization. Moment of inertia of each case is calculated using transformation matrix and its impact on the natural frequency is determined. It is shown that the moment of inertia affects the linear characteristics of the galloping-based energy harvester when the inclination of the cylinder is changed. The nonlinear characteristics and performance of the energy harvester for various inclination angles are carried out. It is indicated that an upright zero inclined or a slight angle of cylinder till ten or fifteen degrees towards the wind flow is preferable for energy harvesting. Any forward inclination towards the wind flow greater than that or any backward angle of cylinder away from the wind flow are not suitable for attaining high levels of harvested power. This behavior actually opens the doors for using a movable cylinder at the tip of a beam with lock mechanism that can be tilted at a high forward or backward angle for extreme windy conditions to have reasonable practical power harvesting without damaging the harvester.