Wake-induced vibration of an inelastic cylinder

A systematic study is conducted both experimentally and theoretically on the wake-induced vibration of an inelastic or zero structural stiffness cylinder placed behind a perfectly elastic or rigid cylinder. The mass ratio m * of the inelastic cylinder is 11.1. The spacing ratio L/D is 2.0–6.0, where L is the distance between centers of the two cylinders, and D is the cylinder diameter. The range of Reynolds number Re is 1.97 × 10 3 –1.18 × 10 4 . It has been found that the inelastic cylinder becomes aerodynamically elastic because the cylinder and the fluctuating wake interact, inducing an effective stiffness and thus giving rise to an aeroelastic natural frequency. This frequency depends on the added mass, fluid damping and flow-induced stiffness and is always smaller than the vortex shedding frequency, irrespective of Re and L/D . The wake-induced vibration of the inelastic cylinder may be divided into a desynchronisation branch and a galloping branch. The vibration amplitude jumps greatly at the transition from desynchronisation to galloping for L/D = 2.0–4.5 but not so for L/D = 5.0–6.0. The flow-induced stiffness is linearly correlated with Re , generally higher in the reattachment regime than in the coshedding regime and smaller in galloping than in desynchronisation. Other aspects of the inelastic cylinder are also investigated in detail, including the dependence on Re of the Strouhal numbers, hydrodynamic forces, phase lag between lift and displacement and flow characteristics.