Switching Events of Wakes Shed From Two Short Flapping Side-by-Side Cylinders

Abstract The wakes shed alternatively from two long stationary side-by-side cylinders have long been an issue in many engineering applications, such as wind energy harvesting schemes that utilize vortex-induced vibrations (VIVs). In this study, switching events of the wakes shed from two “short,” “flapping” side-by-side cylinders are investigated. To this end, the flow visualization and spectral analysis of the time-resolved data from hot-wire anemometers and the piezoelectric mount of flapping cylinders are carried out. Measurements are conducted with differing center-to-center spacing normalized by a single cylinder diameter (T/D)—gap ratio, and length-to-diameter ratio (L/D) in a Reynolds number range of 800 ≤ ReD ≤ 16,000. The results demonstrate the transition of wake shedding patterns, sequentially from a single bluff body wake, first bistable wakes, tristable wakes, second bistable wakes, and eventually to coupled wakes as the gap ratio is increased. Furthermore, the role of shortness and flapping of the two cylinders in determining the wake kinematics is elucidated, and the transitional sequences and switching of dominant shedding frequencies are detailed.