Experimental parametric study on dynamic divergence instability and chaos of circular cylindrical shells conveying airflow

Experiments have shown that soft circular cylindrical shells supported at both ends and conveying airflow lose stability by so-called dynamic divergence. The present study investigates experimentally the effect of geometric parameters of a silicone rubber shell, namely length-to-radius (L/R) and thickness-to-radius (h/R) ratios, on the dynamic divergence instability. Bifurcation diagrams of the rms velocity of the shell vibration versus flow velocity are obtained for different shells, displaying a strongly subcritical nonlinear behaviour. Then, the onset of instability and post-critical behaviour of the shells are compared: (i) thinner and longer shells lose stability at lower flow velocities, (ii) thinner shells have higher rms vibration velocity, and (iii) by decreasing L/R, the subcritical behaviour is weakened for thin shells, while it is strengthened for thick shells. The existence of chaos and the influence of geometric parameters on the chaotic behaviour of the system are deeply examined by means of several measures.