From fluttering to autorotation bifurcation of a flat plate in a current

This paper is dedicated to both the simulation of fluttering (oscillatory) and autorotation of a vertically hinged flat plate that may occur under the action of a fluid current and the experiments of the same vertical flat plate. Fluttering is defined as the oscillation of a body around an axis, whereas autorotation is a continuous rotational mode around the same axis. Both mentioned rotational motions occur without external power, and they are excited by the incident current. This paper describes the simulation of these phenomena by a nonlinear time domain code. The paper also considers the effect of mass moment of inertia on vortex shedding frequency and the resultant dynamics. The main inertia parameter (I*) is defined as the ratio between the mass moment of inertia and the added moment of inertia. It is shown that by increasing I*, fluttering bifurcates to autorotation at I* = 0.162, being the transition approximately independent of the current velocity, or of the corresponding Reynolds number. The results show that Strouhal number drops when fluttering translates to autorotation. Moreover, a method is proposed to calculate the theoretical extractable power from fluttering and autorotation using a phase diagram of angular acceleration versus velocity.