Experimental and theoretical investigation of drag loads on side-by-side flexible blades in a uniform current

This study investigates the hydrodynamic drag loads on side-by-side flexible blades in a uniform current through experimental and theoretical approaches. Four silicone rubber blade models with varying dimensions were arranged side by side in aggregates and tested in a circulating water tunnel. The experiments cover the static regime and the flutter regime. We examine four governing non-dimensional parameters to assess their effects on the bulk drag coefficient C D ,bulk and the onset of flutter: the drag-to-stiffness ratio Ca, the buoyancy-to-stiffness ratio B, the mass ratio of fluid inertia to total system inertia β , and the slenderness parameter λ . The results show that in the static regime C D ,bulk decreases with increasing Ca at a rate closely related to B starting at Ca/B > O (1), and settles to an almost constant value in the flutter regime. Increasing β , B, or λ delays the onset of flutter. By introducing the equivalent thickness and bending stiffness, existing theoretical models for individual blades are utilized to predict drag reduction of side-by-side blade aggregates. The analytical model accurately predicts drag reduction in the static regime, while the numerical model predicts the onset of flutter and drag reduction in both regimes when appropriate cross-sectional hydrodynamic coefficients are applied. Meanwhile, we investigate the reactive force model term by term to identify their impact on system stability and drag reduction, demonstrating its suitability for highly compliant blades in uniform flows.