Predefined angle of attack and corner shape effects on the effectiveness of square-shaped galloping energy harvesters

Energy harvesting based on transverse galloping of a square cylinder has been widely studied while the effects of angle of attack and corner shape remain unclear. This study proposes to explore the impacts of these two parameters on the characteristics and effectiveness of square-based galloping energy harvesting systems using a coupled fluid–structure-electrical model. It is demonstrated that the onset speed of instability is dependent on the electrical load resistance. Additionally, the load resistance value corresponding to the maximum onset speed of galloping is inversely proportional to the natural frequency of the energy harvester. Further, the onset wind speed of instability and the dynamic response of the energy harvester are largely affected by the angle of attack and corner shape. The rounded corners make the onset velocity less sensitive to the angle of attack. The considered square cylinders with different corner shapes exhibit the largest transverse displacements at the angle of attack α0 = 0°, while the displacements at α0 = 2° are only slightly lower than those at α0 = 0°. In general, the rounded corners slightly decrease the displacements and power outputs of the harvester. However, the rounded corners enhance the robustness of the harvester by making its performance less sensitive to the angle of attack within α0 = 0° ~ 6°. It is also shown that the type of instability is strongly dependent on the angle of attack and corner shape which may result in the presence of unexpected bifurcations, such as the subcritical and saddle-node ones.