Amplifying vortex shedding for energy harvesting with active flow control

TL;DR

This paper demonstrates that active flow control via alternate slot blowing can significantly amplify vortex-induced vibrations, potentially improving energy harvesting efficiency by increasing force fluctuations on bluff bodies.

Contribution

It introduces a novel active flow control method using alternate slot blowing to enhance vortex shedding effects for energy harvesting applications.

Findings

Lift fluctuations increased up to three times with actuation.

Streamline bending causes enhanced vortex shedding at optimal frequencies.

Active flow control can significantly boost dynamic loads on cylinders.

Abstract

Energy harvesting from vortex-induced vibrations is a promising technology that relies on the vibrations of bluff bodies due to vortex shedding. Increasing the vibration amplitude at a given free stream kinetic energy is therefore equivalent to enhancing the efficiency of the harvesting device. In this study, we assess the potential of alternate slot blowing to amplify force fluctuations. Pressurized air is ejected alternatingly from the top and bottom parts of the cylinder. Through experimentation in a low-speed wind tunnel ($Re=8,000$), we show that the magnitude of lift fluctuations can be enhanced by up to a factor of three compared to the unforced flow when the actuation is aligned with the natural vortex shedding frequency. Velocity field measurements indicate that this is caused by strong streamline bending whereas, at a higher forcing frequency, vortex shedding is suppressed. The results presented in this article suggest that a significant increase in the dynamic load acting on a cylinder can be achieved with carefully chosen active flow control parameters, thereby promoting future energy harvesting applications.