Dynamics of vortex-induced-vibrations of a slit-offset circular cylinder for energy harvesting at low Reynolds number

Vortex-Induced Vibrations (VIV) offer a safe, renewable, and environmentally friendly energy source for energy harvesting. To enhance the energy-harvesting capability of the circular cylinder-based devices, the authors explore the placement of the normal slit by determining the most effective slit-offset location from the cylinder's center. Using the open-source computational fluid dynamics program OpenFOAM, a series of numerical simulations are conducted to determine the utility of the slit placement on the circular cylinder and how it influences (positively/negatively) the harvester's performance for a 1-degree-of-freedom VIV system. The study shows that the slit cylinder displays the three-branch VIV response [i.e., initial branch (IB), upper branch, and lower branch (LB)]. At a Reynolds number of 150, the cylinder with no slit exhibits the two-branch VIV response (i.e., IB and LB) but lacks the upper branch. This is the first time the upper branch has been acquired for such low Re flows. The results indicate that adding a normal slit to the middle of the cylinder improves the alternating suction and blowing phenomena. Offsetting it from the center toward the back stagnation point suppresses the VIV and makes it unsuitable for energy harvesting applications. While positioning the slit toward the front stagnation point improves aerodynamic lift, the cylinder sheds vortex closer to each other. It enhances the amplitude of transverse oscillation and, consequently, the power extraction. In addition, the peak energy transfer ratio for these scenarios is comparable to that of the no-slit case but with a larger range of peak energy transfer ratio values. It makes it suitable for energy harvesting applications.