Effects of elliptic geometry on energy extraction from flexible cantilever cylinders

A numerical study has been conducted on vortex-induced vibration of different elliptical cylinders with the same natural frequency subjected to uniform flow under lock-in conditions. All six degrees of freedom (6-dof) were restricted at one end of the cylinder, and only transverse and streamwise vibrations (2-dof) were permitted on the other end. The ellipticity factor of the cylinder was varied in the range of 0 ≤ e ≤ 1. A cylinder with a circular cross section (e = 1) exhibits the transverse resonance phenomenon, which shows the strongly coupled transverse and streamwise vibration. The streamwise resonance phenomenon weakens the coupled transverse and streamwise vibration in an elliptical cross-sectioned cylinder (0 < e < 1). Unique streamwise resonance phenomena of an elliptical cylinder are induced by the distinct spanwise wake vortex growth and associated structural vibration. This unique resonance phenomenon of the cylinder enhances both vibration amplitude and frequency in both directions at a specific ellipticity factor (e∼0.5). The enhanced vibration amplitude and frequency aid in the improved energy extraction capacity of the elliptic cylinder when compared with that of the circular cylinder. Hence, the elliptical cylinder can be potentially implemented as an energy harvesting device, such as Vortex-Induced Vibration Aquatic Clean Energy converters.