Wake synergies enhance performance in aeroelastic vibration energy harvesting

This study experimentally demonstrates that a closely spaced array of aeroelastic flutter energy harvesters can exploit synergistic wake interactions to outperform the same number of harvesters operating in isolation. The fluttering motion of each energy harvester imparts an oscillating vortex wake into the flow downstream of the device. Wind tunnel experiments with arrays of two and four flutter energy harvesters show that this wake structure has significant effects on the vibration amplitude, frequency, and power output of the trailing devices. These wake interaction effects are shown to vary with the stream-wise and cross-stream separation distance between the harvesters. Over a defined range of separations, an advantageous frequency lock-in between the devices arises. When this occurs, the trailing harvesters can extract additional energy from the wake of upstream harvesters, causing larger oscillation amplitudes and higher power output in the trailing devices. Experiments to characterize this variation in power output due to these wake interaction effects and to determine the optimal spacing of the energy harvesters are presented and discussed. Smoke-wire flow visualization is used to examine the wake structure and investigate the mechanism of the array interactions.