Experimental investigation of combined vibrations for a hydrofoil-rod system at low Reynold numbers

A hydrodynamic tunnel experimental investigation and analysis of vibration characteristics for a hydrofoil in a transient regime is considered. Tests are performed for NACA 0017 models with a non-uniform section at an angle of attack AOA = 5º and Reynolds numbers up to Re = 7.0 × 106. This study is related to a project design of experiments in a complex facility that involves several parameters. The analysis focuses on the vibrations of a hydrofoil for different values of the bracing stiffness kh, the torsional stiffness ka, and the locations of the elastic axis ā and of the center of gravity xa. The structural bracing response is investigated via measurements of the displacement of the free tip section of the hydrofoil using a three-axis acceleration sensor, and the torsional response of the structure is analyzed via measurements of displacements with single-axis acceleration sensors. The hydrofoil is made of reinforced plastics without flexibility, and elastic functions are provided by a spring support mechanism combined with a torsional structure. The study shows that an increase of the velocity V∞ results in different behaviors of the bracing and torsional amplitudes. Another notable result of the study is that the emergence of transition occurs simultaneously with additional peaks and changes of vibration amplitudes.