Dynamics and performance evaluation of a vortex-induced vibration energy harvester with hybrid bluff body

To investigate the influence of bluff body with a variable section on the vortex-induced vibration (VIV) energy harvesting performance, a series of hybrid cylinders are designed and a quantitative comparison is presented. The basic elements of hybrid bluff body are the D-shaped (D) and original circular-shaped cylinders (O), and the length ratio between the O-shaped part and the D-shaped part is fixed. According to the arrangement order, three kinds of hybrid bluff bodies are termed as ODO, ODODO and DOD. A distributed model is developed and the numerical simulation is carried out to verify the response. Corresponding wind tunnel experiments are conducted, and the results reveal that compared to the bluff body with a circular cylinder, the hybrid bluff bodies such as ODODO and DOD can enhance the VIV and thus increase the output significantly. Moreover, the lock-in regions with the ODODO and DOD shapes will increase by 12.5% and 62.5%, respectively. However, the results also indicate that some type of arrangement such as ODO will suppress the energy harvesting performance. Furthermore, the computational fluid dynamics method is employed to reveal the physical mechanism of flow field around the hybrid bluff body. The results show that the integration of D-shape prism in a cylinder along an axial direction could influence aerodynamics. A faster boundary layer separation occurs for the VIV energy harvesters with the hybrid cylinders of ODODO and DOD, which could improve the energy conversion efficiency from flow-induced vibrations. However, the aerodynamic force is restricted and response is suppressed as a D-shaped cylinder is sandwiched between two O-shaped cylinders.