The effect of damping and aspect ratio on power extraction from vortex-induced vibration of elliptical cylinder

Vortex-induced vibration (VIV), a type of flow-induced vibration, is a relatively new means of generating clean energy. The present study aims to quantify the flow-power extraction using the elastically mounted elliptical cylinders of different aspect ratios (AR). The power extraction process is modeled using a linear damper attached to the moving cylinder. The mass ratio of the vibrating structure ( m*) is kept constant at 10, and the Reynolds number is taken as 100 for the 2D numerical simulation. The aspect ratio of the elliptical cylinder varies from 0.10 to 1.00 (circular cylinder), and the damping ratio ( zeta) ranges from 0.02 to 0.12. The vibration amplitude response of the elliptical cylinders is found to be similar to that of the circular cylinder, consisting of initial and lower branches. The maximum vibration amplitude and the width of the synchronization region of the elliptical cylinders are observed to increase with decreasing AR. For each AR, there is an optimum mass-damping parameter, alpha=m*zeta where the time-averaged power ( P-alpha<overline>) output is at its peak value ( P<overline>(peak)). The peak power ( P<overline>(peak)) output is a non-monotonic function of AR. The elliptical cylinder with AR = 0.40 is found to maximize P<overline>(peak). To the circular cylinder (AR = 1.00), it attains a 62.37% increase in P<overline>(peak) and a 24.40% increase in power extraction efficiency ( eta). When compared to the circular cylinder, elliptical cylinders are found to produce significantly more power over a wider range of alpha. Thus, elliptical cylinders are better suited for VIV-based hydrokinetic energy extraction devices.