Investigation of a submerged fully passive energy-extracting flapping foil operating in sheared inflow

TL;DR

This study computationally investigates a fully passive, energy-extracting flapping foil in sheared and free surface conditions, revealing performance enhancements in shear but deterioration near the free surface due to vortex interactions.

Contribution

It introduces a coupled CFD and rigid body dynamics simulation framework for analyzing passive energy harvesters in complex flow conditions, including free surface effects.

Findings

Performance improves under sheared inflow.

Free surface interaction reduces energy extraction efficiency.

Simulation results align with existing experimental data.

Abstract

In this work a fully passive energy harvesting foil is studied computationally. An in-house 2nd order finite volume CFD solver, MaPFlow, is strongly coupled with a rigid body dynamics solver to investigate the foil operation under uniform and sheared inflow conditions with/without free surface. The mesh follows the airfoil motion using a radial basis function (RBF) mesh deformation approach. Initially, MaPFlow predictions are compared to experimental and numerical results available in the literature, where reasonable agreement is found. Next, one-phase simulations are considered for linearly sheared inflow for various shear rates. Results suggested that foil performance can be enhanced under sheared inflow conditions. Finally, two-phase simulations taking into account the free surface, for both uniform and sheared inflow, are considered. Predictions indicate a significant deterioration in performance of the system when the foil operates under the free surface due to the interaction of the shed vorticity with the free surface.