Vortex-Induced Vibration of Two Rigidly Coupled Cylinders in Tandem Arrangement With Low Mass Ratios

Vortex-induced vibration (VIV) of two rigidly coupled cylinders in tandem arrangement with a fixed center-to-center separation of 2 (s/D = 2) is numerically investigated in a laminar flow with Re = 150. Results are examined over a domain of reduced velocities ranging from 0.25 to 100 and very low mass ratios are considered, i.e., m* = 0.02, 0.1, 0.3 and 0.9, respectively. It is found that the amplitude at the infinite reduced velocity increases smoothly as the mass ratio decreases, whereas the amplitude experiences a sharp increase for an isolated vibrating cylinder below the critical mass ratio at the same Reynolds number. Interestingly, unlike the VIV of an isolated cylinder, the time traces of the displacement is quasi-periodic in the first part of the low branch for the two-cylinder system. This so called beating phenomenon is identified as a consequence of the different flow state, particularly the presence or absence of an active gap flow. The present study highlights significant distinctions in the amplitude response associated with wake patterns between the VIV of the two-cylinder system and that of the isolated cylinder.