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 < 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.
Highlights
Flapping or galloping energy harvesters are promising solutions to scavenge energy from airflow via vortex induced vibrations (VIV)
Based on previous work [20,21,22,23], the flapping airflow energy harvester investigated here is composed of a cantilever beam made of Beryllium copper, a wing attached to the free end of the cantilever with an attacking angle α of 10∼15◦ (Figure 1), a bluff body placed in front of the wing with airflow coming towards it
This paper presents mechanical intervention methods to enhance the performance of a cantilever-based flapping airflow energy harvester by increasing flow velocity and using external magnetic excitation
Summary
Flapping or galloping energy harvesters are promising solutions to scavenge energy from airflow via vortex induced vibrations (VIV). Reported flapping energy harvesters are generally designed based on flapping foils or a clamped beam with a bluff body. Bibo and Daqaq [10] developed a piezoelectric galloping harvester and established a universal response relationship between the power output and flow velocity to evaluate the performance of three bluff body configurations—a square section, a semi-circle section and a triangle, among which the square section outperforms the others. Dai et al [15] developed a galloping electromagnetic energy harvester, with the bluff body at the free end of the beam substituted by a magnet oscillating in a coil and generating power. The flapping airflow energy harvester, based on a cantilever beam, may stop oscillating or vibrate in the second mode with the increase of electrical damping, being unable to achieve its optimum performance. The effects of airflow velocities and of external magnetic excitation on power output are investigated experimentally with results presented and discussed
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