Experimental and numerical investigation of drag loads on side-by-side flexible blades in large-amplitude oscillatory flows

This study investigates hydrodynamic drag forces on side-by-side flexible blades in large-amplitude uniform sinusoidal oscillatory flows using both experimental and numerical approaches. Four distinct blade models, fabricated from silicone rubber with varying dimensions, are arranged in side-by-side aggregates and subjected to forced oscillations. Flutter is observed under conditions of large flow excursions and high blade flexibility, revealing a flutter regime not accounted for by the four kinematic regimes reported in the literature. This oversight in existing studies results from the neglect of structural inertia. The results show that flutter significantly affects the drag loads on the flexible blades and their structural response, implying that theoretical studies of flexible blades under extreme conditions must account for structural inertia and flutter. Parametric trends show that the onset of flutter is delayed to larger Cauchy numbers (drag-to-stiffness ratio) by increasing the buoyancy-to-stiffness ratio or the mass ratio of fluid inertia to total system inertia. Earlier flutter onset at smaller Cauchy numbers generally corresponds to a higher bulk drag coefficient in the flutter regime.