Dual flapping foil system for propulsion and harnessing wave energy: A 2D parametric study for unaligned foil configurations

Dual flapping foil systems are a promising concept able to improve overall ship propulsion performance and recover wave energy, reducing fuel consumption and making maritime equipment eco-friendlier. In this context, the present article aims to present a 2D parametric study of a flapping foil system able to operate in two modes: energy harnessing and propulsion. First, a brief theoretical review is presented, followed by the numerical approach used and the validation tests performed. The main goal of the parametric study is to analyse how the out-of-phase configuration and the spacing interfoils influence the results in terms of hydrodynamic coefficients and power output, when compared to the baseline (foils aligned). Implementing the cases using the kappa - omega SST turbulence model, combined with the overset 6DOF approach for the foil motion from the commercial CFD tool ANSYS (R) Fluent (R), it was possible to show that cases 1 & 2 (unaligned, spaced configuration) presented a better overall performance for the two operation modes.