Computational Analysis of Energy Harvesting Potentials of Flow-Induced Vibrations for Micro Power Generators

Abstract

Energy harvesting through various flow-induced vibrations is being extensively studied for the last two decades. The focus of this work is to numerically simulate transverse galloping and vortex-induced vibration phenomena of square and trapezoid cylinders for energy harvesting at various angles of incidence (α). Effect of tail on response of trapezoid is also investigated. The structure is modeled as elastically mounted supported by linear spring and damper. Incompressible Navier-Stokes equations are the governing equations for the flow. Geometry and mesh are created in ANSYS design modeler and ANSYS mesh, respectively. The mass ratio (m∗) is set as 15.1 while the damping ratio (η) is 0.00295 giving mass-damping ratio (m∗η) of 0.0000695. In the current study, α is varied from 0◦ −20◦. Numerical simulations are performed in ANSYS Fluent at Reynolds number (Re) of 2500 based on the in-flow velocity and the width of the cylinder. The flow field is simulated using Spalart-Allmaras turbulence model. The solution procedure is programmed by a user define function (UDF) dynamically hooked to ANSYS Fluent. Wind-induced transverse vibration of the bodies (galloping and vortex-induced vibration) are then simulated at different reduced velocities. The simulated data is also compared with those of previous experimental work. Results demonstrate that trapezoid body has an extended range of galloping instability as compared to a square cylinder thus providing better energy harvesting potential. Addition of tail also has significant effect. As much as 24-45% increase in amplitude is observed with the addition of tail with trapezoid. Based on the simulations, trapezoid with 0.4D tail outperforms 0.8D tail trapezoid.