Piezoelectric Energy Harvesting from von Karman Vortices
In this paper a study of an innovative energy-harvesting system based on a piezoelectric converter to recover energy from an airflow is presented. The converter is embedded as a part of an oscillating beam, and it is used to harvest energy from the vibrat
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Introduction
The recovery of energy from von Karman vortices can be effective since they are common behind obstacles immersed in a flow (at Reynolds numbers Re 300–600) and they represent an ideal forcing for a vibrating energy harvester due to the conversion of a unidirectional (DC) flow into an alternated (AC) periodic pressure field [1]. In this work an energy-harvesting system where von Karman vortices excite an oscillating beam is proposed. The vortices are generated by a bluff body immersed in an airflow, and they are collected by placing the beam in the vortices region [2]. A piezoelectric converter has been embedded in the beam to harvest energy from the generated oscillations. The system composed of the bluff body and the beam has been placed in a wind tunnel with the possibility to direct the beam with different orientation angles with respect to the flow direction and to generate different flow velocities. In this way the harvesting effectiveness can be investigated as a function of these two different parameters. In fact, the orientation angle affects the interaction between the beam and the forcing pressure field. On the other hand, the repetition frequency of the vortices and the coupling with the mechanical beam resonance depend on the flow velocity [3].
M. Demori (*) • V. Ferrari Department of Information Engineering, University of Brescia, Via Branze 38, Brescia 25123, Italy e-mail: [email protected] S. Farisè • P. Poesio Department of Mechanical and Industrial Engineering, University of Brescia, Via Branze 38, Brescia 25123, Italy 417 C. Di Natale et al. (eds.), Sensors and Microsystems: Proceedings of the 17th National Conference, Brescia, Italy, 5-7 February 2013, Lecture Notes in Electrical Engineering 268, DOI 10.1007/978-3-319-00684-0_80, © Springer International Publishing Switzerland 2014
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Fig. 1 Schematization of the system: the bluff body is placed perpendicular to the flow direction, and it is 20 mm thick and 55 mm wide; the beam is composed of the piezoelectric converter, with 45 mm length and 20 mm width, and the blade, with 70 mm length and 30 mm width
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System Description
A parallelepiped-shaped obstacle has been placed in a wind tunnel, and it acts as bluff body for the generation of the vortices. As shown in Fig. 1, the oscillating beam system has been placed behind the bluff body. The beam is composed of the piezoelectric converter and a blade profile. The converter is a bimorph piezoelectric element, WAC3X/18, with internal impedance composed of a capacitance CP ≈ 270 nF and a parallel resistance RP ≈ 20 kΩ measured at a frequency of 100 Hz. The converter is based on a steel slat, which has been clamped at one end to obtain a cantilever structure. The blade has been connected to the free end of the converter to collect the alternate pressure field of the vortices as the forcing for the oscillation. A tailored clamp to connect the beam to the shaft of a stepper motor has been manufactured. In this way the stepper motor allows to vary the orie
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