Generation mechanism of wake galloping in two staggered circular cylinders in view of hysteretic flow phenomena

A smooth cylinder placed near the wake of an upstream smooth cylinder is susceptible to galloping. This study experimentally investigated the generation mechanism of wake galloping in two staggered cylinders of equal diameter D based on the physical flow phenomena occurring in the oscillating downstream cylinder. The horizontal center-to-center distance of the two cylinders ranged from 3.0D to 3.5D and the vertical center-to-center distance was 0.3D to 0.5D. As observed, the wind velocity range in the smooth cylinder was within the subcritical Reynolds number regime, and the unsteady responses at the downstream exhibited prominent hysteresis that evolved with the reduced velocity, and ultimately, triggered wake galloping at the critical reduced velocity. In particular, this hysteretic behavior is native to certain arrangements of the two cylinders and occurs because of the interaction between the downstream cylinder and the wake of the upstream cylinder. Moreover, the hysteresis-based discussion could identify the potential wake galloping vibrations in certain arrangements that are beyond the scope of the current investigation. With the application of 12 spiral protuberances on the surface of both cylinders, the hysteresis vanished and wake galloping was suppressed