Importance of gravitational effects on the performances of a fully passive oscillating-foil turbine deployed horizontally

This article presents a numerical study evaluating the impact of gravity on the performance of a fully passive oscillating-foil turbine operating in a horizontal configuration, that is, where the gravity acts along the heave direction. The study examines two sets of parameters corresponding to turbines driven by different aeroelastic instabilities. For turbines experiencing stall-flutter instability, the influence of gravity on performance metrics is minimal when inertial forces dominate or are comparable to gravitational forces. At high Froude numbers, buoyancy and weight are negligible, but their impact increases at lower Froude numbers, leading to reduced performance. Conversely, turbines operating through coupled-flutter instability seem unsuitable for horizontal configurations since they require high foil moment of inertia and mass, which amplifies the effects of buoyancy and weight, thereby diminishing performance at any Froude number.