Fluid-structure interactions in energy harvesting and bio-inspired propulsion systems

The interactions between fluids and structures can lead to diverse phenomena, depending on the direction of energy transfer. When structures extract energy from fluids, their interactions can induce self-sustained oscillations, offering innovative solutions for renewable energy harvesting. Conversely, when structures inject energy into fluids, their interactions can lead to the generation of thrust, as in the case of fish swimming. In the first part of the talk, I will discuss the flow-induced oscillations of pitching wings, highlighting the onset of two distinct oscillation modes: a high-inertia structural mode and a low-inertia hydrodynamic mode. These discussions will then extend to swept wings, where 3D flow structures, captured using multi-layer stereo Particle Image Velocimetry, are correlated with unsteady aerodynamic forces through a physics-based Force and Moment Partitioning Method. In the second part of the talk, I will shift the focus to the hydrodynamics of ray-inspired fins swimming near a substrate. Using experiments with a ray-inspired robotic platform, potential flow simulations, and 3D flow measurements, I will demonstrate that near-ground lift depends strongly on fin wavenumber. These results suggest that the stronger suction forces associated with lower wavenumber may help explain the depth-dependent kinematics of rays and ray-inspired robots. In summary, understanding the complex interactions between unsteady fluid dynamics and structural dynamics is crucial for modeling and optimizing energy harvesting and bio-inspired propulsion systems, and for uncovering new design principles for engineered fluid-structure systems.