Fluidelastic modeling of a weathercock stabilization in a uniform flow

The relaxation dynamics of a weathercock free-to-rotate, in the presence of a uniform flow, as it aligns with the flow direction, is investigated experimentally in a wind-tunnel. The dynamics is observed to conveniently follow a damped harmonic oscillator behavior. At first order, the frequency is set by the aerodynamic coefficients. We show that a quasi static approach fails to precisely describe the relaxation dynamics and that non-stationary corrections are required to model the dynamics. A first strategy is to introduce added mass, added stiffness and added damping to the quasi-static approximation, following what is usually done in the context of vortex-induced vibrations. A second strategy is to introduce empirical corrections, whose scaling is obtained from the analysis of the experimental data. Finally, these two strategies are compared and we discuss the physical interpretations of the non-stationary corrections.