Experimental Study of Flow-Induced Oscillations of Flexible Structures with Non-Circular Cross Sections*

Flow-induced oscillations of flexible structures with non-circular cross sections, including a square prism and symmetric hydrofoil with a NACA 0021 profile, are studied experimentally over a range of flow velocities. The flexible structures are made of silicone rubber and are strung horizontally across the test section with the flat side of each structure, i.e. the side length of the square prism and chord length of the hydrofoil, placed perpendicular to the direction of the incoming flow. Experiments are conducted in a recirculating water tunnel whereby displacement of the structure is recorded using high speed cameras in the crossflow and inline directions. Displacement along the length of each structure is then quantified using an in-house MATLAB code. Performed simultaneously with the displacement measurements, hydrogen bubble flow visualization reveal the vortex shedding patterns observed in the wake of the flexible structure. Various types of oscillations are observed depending on the structures’ cross section and flow velocity, including vortex-induced vibrations, galloping and mono- and multi-frequency responses at low- and high-mode-numbers.