Numerical investigation of the fluid-structure interaction of a three-dimensional flexible pitching plate

This research numerically investigates the effect of flexibility on the hydrodynamic efficiency of a pitching flat plate. A sinusoidal pitching motion of frequency 0.6, 1.5, and 2 Hz is imposed on the flexible plate immersed in a hydrodynamic flow, at a laminar Reynolds number of 2000. The fluid-structure interaction (FSI) problem is solved with the computational fluid dynamics code FINE/Marine using a modal approach. A parametric study is carried out on the pitching frequency and the flexibility of the plate, to characterize the combined effects of FSI and pitching motion on the hydrodynamic loads. This work contributes to the understanding of hydrodynamic performances of structures operating with high-dynamic motions combined with a significant level of flexibility. First, the influence of the pitching frequency for a rigid plate is analyzed. It is shown that the amplitude of the hydrodynamic coefficients increases with the pitching frequency and their phase is shifted, due to the plate's angular acceleration. The production of lift is found to be a combination of the vortex dynamics and the acceleration effects due to pitch oscillation. The acceleration effects become prevalent over the vortex dynamics at higher pitching frequencies. In the flexible case, it is highlighted that the synchronization of the acceleration effects due to the vibration of the plate and the pitching motion has a crucial influence on the hydrodynamic forces. In the studied range of pitching frequencies, the lift is increased by a factor of 5.5 due to the pitching motion and up to a factor of 2 due to the flexibility. A ratio between the pitching frequency and the natural frequency of the plate is introduced to characterize the effect of flexibility.