Fluid–structure interaction of a flexible rotor in water

Abstract In this study, a moderately flexible rotor is investigated experimentally in a water channel. The rotor consists of a single blade with a simplified rectangular geometry and is tested with various pitch angles at different rotational speeds. The flapwise bending deformation and induced torsion of the blade are measured using image processing tools, and flow fields are extracted with Particle Image Velocimetry. The blade deformation behaviour depends strongly on the pitch angle, it includes extreme downstream and upstream bending for high negative and positive pitch, respectively. In addition, large-amplitude, low-frequency bending fluctuations are observed in a certain range of rotational speeds for negative pitch. The wake vorticity fields show large-scale recirculation zones being formed and intermittently shed behind the rotor, resembling the dynamics of the Vortex Ring State known from helicopter aerodynamics. A comparison with the flow generated by a rigid rotor of the same geometry is also carried out.