Energy generation is never an outdated topic especially in the modern societies, where the climate change due to the global warming requires shift from the traditional fossil fuels to new renewable energy technologies. It is well recognized that the hydrokinetic energy (energy extracted from tidal, ocean and river currents) can be a significant contributor to the renewable energy portfolio. Traditionally the hydrokinetic energy is extracted and converted to electricity by a turbine or arrays of turbines. Installation of such devices in the rivers can have a significant environmental impact to the distribution of sediments, nutrients, and the aquatic ecosystems. A new approach that adopts vortex induced vibration (VIV) to passively harvest energy from the river current shows its potential to challenge traditional hydrokinetic energy generation. The VIV is a fluid-structure interaction resulting in a limited amplitude self-excited oscillation caused by periodic forces exerted by the flow on an oscillatory system (Lin et al., 2018). A VIV generator transfers the kinetic energy of the fluid flow into mechanical vibrations of a bluff body which in turns, converts mechanical energy of vibrations to electricity. Systems used to convert energy of vibrations into electricity are based on piezoelectric, electromagnetic, and electrostatic methods. Regardless of the method of conversion, the efficiency of a VIV generator is dependent on frequency, amplitude, and minimum flow speed to trigger the generator. Large energy transfer/generation occurs at large amplitude oscillations when the vortex shedding and the structural vibration frequencies coincide, a condition referred to as “lock-in”. It was shown by Govardhan & Williamson (2000) that the lock-in region can be infinitely extended, while the mass ratio defined as the density of the solid bluff body to the density of the fluid approaches zero. Therefore, having generator with tethered neutrally or slightly positively buoyant bluff body for a VIV harvester should facilitate “lock-in” high amplitude vibrations.

In this paper, the performance of a single- VIV generator and an array of VIV generators is investigated experimentally.  The generator consists of a tethered slightly positively buoyant bluff body (cylindrical, spherical) free to move in both in-line and crossflow directions. The array of generators consists of ten tethered buoyant cylinders that are positioned in different parallel and staggered formations. It was observed that the Reynolds number influences the response amplitudes, but in all cases, similar fluid–structure interaction mechanism was observed, resulting in high-wavenumber vortex-induced vibrations consisting of a mixture of standing and traveling wave patterns. In addition, this study presents investigation of the optimal geometry in terms of the lengths, mass and density of the generator/s in order to maximize the harvested power.


Hydrokinetic Vortex Induced Vibration (VIV) Energy Harvester

Division / Sponsors: 
Aerospace, Bioengineering, Applied Mechanics, Design Engineering Division, Advanced Energy Systems, Manufacturing Engineering Division, Noise Control and Acoustics, Nondestructive Evaluation, Diagnosis, and Prognosis (NDPD), Nuclear Engineering Division, Process Industries Division, Fluids Engineering, Heat Transfer, Materials, Microelectromechanical Systems, Safety Engineering and Risk Analysis, Computers & Information in Engineering


Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2020/volume/84478

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