Enhancing Output Power of a Cantilever-Based Flapping Airflow Energy Harvester Using External Mechanical Interventions

Abstract

This paper presents a flapping airflow energy harvester based on oscillations of a horizontal cantilever beam facing the direction of airflow. A wing is attached to the free end of a cantilever beam and a bluff body is placed in front of the wing from where vortex falls off, producing vortices under the wing and driving it to oscillate. An electromagnetic transducer is integrated to convert the flow induced vibration into electrical energy. This flapping energy harvester, however, may stop oscillating or vibrate in the second mode under high electrical damping, and thus may be unable to achieve its optimum performance. Simple yet effective mechanical interventions can be applied to the harvester to enhance its power output, i.e., to increase flow velocity and to apply external magnetic interaction. The effect of airflow velocities on output power was investigated experimentally and the results show that the energy harvester scavenges more power in airflow at higher Reynolds numbers (higher flow velocity at R e < 24,000). The external magnetic excitation is achieved though placing one magnet to the wing and another one above the wing to induce a repelling force, aiding the beam to oscillate in high electrical damping. Experimental results show that the power output can be enhanced by 30% when the magnet interaction is properly integrated.

A Flapping Airflow Energy Harvester with Flexible Wing Sections

“…Each prototype was tested with the resistive load ranging from approximately 1 kΩ to 400 kΩ. The optimal loads are influenced by system damping and dependent of wind velocity and wing design [9]. The maximum power at optimum loads was used to evaluate the improvement of flexible wing design on power output.…”

“…This study focuses on a specific type of flapping airflow energy harvesters that typically have a wing with a relatively large area to generate sufficient lift force to initiate the wing oscillation [8][9][10]. The large area rigid wing in this type of flapping airflow energy harvester, however, will encounter high aerodynamic resistance.…”

“…As a result, they have higher mechanical damping during its oscillation, which reduces output power of such energy harvesters. Progresses have been made to improve performance of such energy harvesters by using external mechanical interventions [9]. This paper will introduce a new method to improve performance of a flapping harvester based on rigid wings and electromagnetic conversion [8][9][10][11] by applying flexible wing sections to the original design.…”

“…Progresses have been made to improve performance of such energy harvesters by using external mechanical interventions [9]. This paper will introduce a new method to improve performance of a flapping harvester based on rigid wings and electromagnetic conversion [8][9][10][11] by applying flexible wing sections to the original design. Flexible wings are usually applied on micro air vehicles at low Reynolds number (10 3 -10 5 ) for improved aerodynamic efficiency, better lifting and thrusting forces [12][13][14].…”

Influence of Shape and Piezoelectric-Patch Length on Energy Conversion of Bluff Body-Based Wind Energy Harvester

“…In addition, many wind-induced vibration energy harvesters have been proposed [12]. Lots of studies proved that it is feasible to harvest wind-induced vibration energy through piezoelectric materials [28][29][30][31][32][33][34]. However, improving the electromechanical conversion efficiency and power density for wind-induced vibration energy harvesters is an urgent problem to be solved.…”