Experimental Investigation of Reynolds Number and Spring Stiffness Effects on Vortex-Induced Vibration Driven Wind Energy Harvesting Triboelectric Nanogenerator

Abstract

Vortex-induced vibration (VIV) is a process that wind energy converts to the mechanical energy of the bluff body. Enhancing VIV to harvest wind energy is a promising method to power wireless sensor nodes in the Internet of Things. In this work, a VIV-driven square cylinder triboelectric nanogenerator (SC-TENG) is proposed to harvest broadband wind energy. The vibration characteristic and output performance are studied experimentally to investigate the effect of the natural frequency by using five different springs in a wide range of stiffnesses (27 N/m<K<90 N/m). The square cylinder is limited to transverse oscillation and experiments were conducted in the Reynolds regime (3.93×103−3.25×104). The results demonstrate the strong dependency of VIV on natural frequency and lock-in observed in a broad range of spring stiffness. Moreover, the amplitude ratio and range of lock-in region increase by decreasing spring stiffness. On the other hand, the SC-TENG with higher spring stiffness can result in higher output under high wind velocities. These observations suggest employing an adjustable natural frequency system to have optimum energy harvesting in VIV-based SC-TENG in an expanded range of operations.

Keywords: spring stiffness; triboelectric nanogenerator; vortex-induced vibration; wind energy.

Figure A1

Comparison of the number of PTFE balls accommodated between square-grid structure and honeycomb structure.

Figure A2

Experimental apparatus of the vibration characteristics of the SC-TENG.

Figure A3

Experimental apparatus of the output performance of the SC-TENG.

Figure A4

Effects of the size of PTFE ball on the output of the SC-TENG.

Figure 1

Design and working mechanism of the SC−TENG. (a) Schematic diagram and structure of the SC−TENG: (i) application scenario of the SC−TENG, (ii) structure of the SC−TENG, (iii) detailed structure of the power generation unit; (b) experimental setup in the wind tunnel; (c) vortex-induced vibration of the SC−TENG; (d) four working states in the process of power generation; (e) potential simulation diagrams of four working states.

Figure 2

(a) Schematic of smoke wire visualization experimental arrangement. Smoke wire visualization of fluid interaction with the square cylinder at (b) 1.6 m/s, in which (i–iv) vortex development process and (c) 7.5 m/s, in which (i–iv) vortex development process.

Figure 3

Vortex-induced vibration characteristics. (a) Amplitude ratio as a function of reduced velocity for different spring stiffness cases; (b) Amplitude ratio versus Reynolds number for different spring stiffness cases; (c) nondimensional frequency of response (f^*) versus nondimensional velocity (U^*) for different spring stiffness cases.

Figure 4

(a–c) Dependence of the output performance of the SC−TENG with $K=27 \mathrm{N}/\mathrm{m}$ on the wind velocity; (d–f) dependence of the output performance of the SC−TENG with $K=55 \mathrm{N}/\mathrm{m}$ on the wind velocity; (g–i) dependence of the output performance of the SC−TENG with $K=90 \mathrm{N}/\mathrm{m}$ on the wind velocity.

Figure 5

Demonstration of the SC−TENG. (a) The output current and the power of the SC−TENG with respect to resistance in the circuit; (b) charge curve of the SC−TENG under different velocities; (c) durability test of the SC−TENG; (d) more than 200 LED light bulbs are lit by the SC−TENG; (e) a thermometer powered by SC−TENG; (f) the charge-discharge curve of the SC−TENG system powering thermometer.