# Kinematics and dynamics of pitching flexible panels in a quiescent fluid

Deshpande, P and Vishwasrao, A (2021) Kinematics and dynamics of pitching flexible panels in a quiescent fluid. Journal of Fluid Mechanics, 922. ISSN 00221120

An experimental investigation was carried out to understand the kinematics and dynamics of flexible panels having pure pitching motion in a quiescent fluid. Simultaneous measurements of force and angular position of a panel were performed for various panel configurations. A high-speed camera imaging technique was used to find the instantaneous position of the trailing edge. The wake vortex flow was also quantified using the particle image velocimetry technique (PIV). We established a generic correlation between a time-averaged thrust coefficient $C_T$ and an effective flexural stiffness $\varPi$ of the panel. The results in terms of both time and phase-evolution of hydrodynamic forces and torque are exhibited through the complete kinematics and dynamics of the pitching panels, perhaps for the first time. The elastic deformation of the flexible panel at stroke reversals is found to affect the longitudinal force generation significantly when compared with the rigid panel. We have described many interesting features related to the elastic deformation of the panel. During stroke reversal, the motion of the pitching for the flexible panels reduces when compared to the pitching motion imposed by the forcing function. Reduced panel motion is found to aid thrust generation for a longer time in a cycle for which magnitude is indirectly governed by the flexural stiffness of the panel. The onset of instantaneous thrust and trailing-edge vortex generation is found to match precisely with the spatio-temporal location of the panel inflection. We noted that both the maximum phase lag $\phi$ and corresponding hydrodynamic torque $T_{hyd}$ are strongly correlated to the panel's effective flexural stiffness $\varPi$.