On the electrode segmentation for piezoelectric energy harvesting from nonlinear limit cycle oscillations in axial flow

Aeroelastic energy harvesters can be used for low-power electricity generation in various applications ranging from aircraft and rotorcraft to civil structures in high wind areas. Among the various alternative transduction mechanisms for airflow energy harvesting, piezoelectric energy harvesting from limit cycle oscillations of cantilever beams in axial flow has been pointed out as a geometrically scalable and simple option. The dynamic deformed shape of flexible beams during limit cycle oscillations involves more complex motions than simple standing waves and mode shapes. Such deformations yield moving strain nodes (inflection points), where the dynamic bending strain changes sign. As a result, the use of segmented piezoelectric layers to avoid charge cancellation is more involved as compared to modal vibration problems that have fixed strain nodes. To alleviate this issue without implementing complex optimization schemes, this work presents a criterion for segmentation of the piezoelectric layers to enhance the power extraction from aeroelastic limit cycle oscillations of a flexible cantilever in axial flow, based on a cyclic average of the strain node motion. A fluid-structure interaction model that couples the nonlinear governing equations of an electromechanically coupled beam with an unsteady aerodynamic model is implemented, and wind tunnel experiments are performed for validation. Theoretical predictions of the electromechanical response for a piezoelectric bimorph cantilever in axial flow are experimentally validated for both continuous and segmented configurations of the piezoelectric layers. More than 30% enhancement in the electrical power output is observed when piezoelectric layers are segmented based on the criterion given here.