Scaling the thrust and deformations of a rotor with flexible blades

Adding flexibility to rotating structures has been shown to improve their efficiency and reliability as well as their compliance to external flow perturbations. Here, we experimentally investigate the problem of a propulsive rotor submerged in water with flexible blades in both spanwise and chordwise directions. When we rotate the propeller and set an incoming flow, the blades bend and twist. We report measurements of forces and associated blade deformations. We show that moderate deformation affects the thrust produced by the rotor within a few percent while strong deformation completely inhibit thrust production. We show that the bending angle of the blade can be predicted thanks to a modified Cauchy number, taking into account the angle of attack of the blade, in the limit of small deformations. Finally, we show that there exists a single curve linking the thrust produced by the rotor to the bending deformation.