Numerical investigation on VIV energy harvesting enhancement with adding eccentricity to a circular cylinder

In recent years, energy harvesting from vortex-induced vibration (VIV) of a cylinder as a renewable source of energy has been increased. The main goal is to enhance the harnessed hydrokinetic energy of the VIV converters. In this work, the effect of adding a rotational degree of freedom by giving eccentricity to the circular cylinder is investigated on vibration and rotational response as well as hydrokinetic energy conversion. Simulations are done at the Reynolds number ranging from 2×10^3 to 13×10^3. Twodimensional unsteady Reynolds-averaged Navier–Stokes equations (URANS), supplemented with SST turbulence models, are solved on moving mesh, and arbitrary Lagrangian-Eulerian formulation is employed to accommodate the deforming boundaries. For the freely rotating and vibrating cylinder, results demonstrate that increasing the inlet velocity increases the vibration amplitude, and the cylinder experiences complete rotation in some of the flow times. Moreover, adding a rotational degree of freedom causes hydrodynamic instability, in which the location of separation points changes and makes a wide wake pattern with unstable vortexes behind the cylinder. As a result, the harnessed power and energy conversion efficiency of the system is increased. The freely vibrating-rotating system generates a maximum power of 0.024 (W), and the energy conversion efficiency increases and fluctuates around 11.2%.