Session: 08-25-01: Flow-Induced Vibrations of Energy Systems

Paper Number: 164740

Feasibility of an Airfoil-Based Wind Energy Harvester Operating in Deep Stall Conditions Under Reverse Flow: A Preliminary Experimental Study 

With the global transition toward renewable energy, recent studies have explored various wind energy harvesting methods, including galloping, vortex-induced vibration (VIV) of bluff bodies, and coupled or torsional flutter of airfoil-based harvesters. While these approaches have demonstrated feasibility, certain limitations persist, such as susceptibility to turbulence (galloping-based), narrow operational wind speed ranges (VIV-based), and complex design requirements (coupled or torsional flutter-based). As an alternative, this study investigates airfoil-based stall flutter in reverse flow as a mechanism for wind energy harvesting. This promising yet underexplored phenomenon, observed in the rotor blades of high-speed helicopters and wind turbines, leverages massive flow separation and unsteady aerodynamic loads to induce flutter, making it well-suited for energy harvesting. To explore the feasibility of this mechanism, a novel airfoil-based harvester is proposed, designed to operate in deep stall conditions under reverse flow. Compared to existing designs, this harvester is simpler and offers several advantages, including efficient performance at low wind speeds, large self-sustained pitching amplitudes, reduced sensitivity to turbulence, and the ability to sustain limit cycle oscillations.

A prototype apparatus has been developed for wind tunnel testing to experimentally validate the proposed concept. The experimental setup consists of three main components: (1) a vertically oriented, rigid NACA0012 airfoil fabricated from polylactide (PLA) via 3D printing, which rotates about a pivot axis; (2) two coil springs positioned at the top and bottom of the blunt trailing edge to facilitate flapping motion while introducing torsional flexibility; and (3) a vertical aluminum support rod securing the model to the wind tunnel floor. Initial tests in Northeastern University’s wind tunnel under uniform flow conditions establish the operational wind speed range and onset flutter velocity, followed by tests under turbulent flow conditions to assess sensitivity to turbulence. The aerodynamic loads on the support structure and the flapping motion of the prototype apparatus are recorded using an ATI Gamma SI-130-10 six-axis force transducer and a Micro-Epsilon optoNCDT 1420 laser triangulation sensor. Experimental results provide insights into the harvester’s dynamic response and feasibility, laying the groundwork for integrating a piezoelectric patch or an electromagnetic coupling mechanism to convert flapping motion into usable electricity.

Results indicate that the proposed airfoil-based wind energy harvester can trigger reverse flow stall flutter at relatively low wind speeds and sustain high-amplitude flapping across a wide range of wind velocities, reinforcing its potential as an effective wind energy harvesting solution. Additionally, integrating polyvinylidene fluoride (PVDF) films into the coil springs successfully converts flapping motion into electricity at low and moderate wind speeds, confirming the practical viability of this approach for energy harvesting.

Presenting Author: Tuan Kiet La Northeastern University

Presenting Author Biography: Tuan Kiet La is currently a Ph.D. student at the Department of Civil and Environmental Engineering, College of Engineering, Northeastern University and a Research Assistant at the Northeastern Wind Engineering Research Group.

Authors:

Tuan Kiet La Northeastern University
Luca Caracoglia Northeastern University