Effect of pulsatile flow on hydrodynamic characteristics of vortex induced vibration of square cylinder

Abstract

Vortex Induced Vibration (VIV) of an elastically mounted square cylinder subjected to pulsatile flow conditions is solved numerically for Reynolds number (Re = 100) and low mass ratio (Mred = 2). The focus of the present work is on investigating the effects of pulsatile frequency on the response of the cylinder. Effects of variation in Keulegan-Carpenter number, KC ϵ [10- 40, step of 10] and reduced velocity, Ured, ϵ [3-25, step of 1], on hydrodynamic characteristics is studied. An Arbitrary-Lagrangian Euler (ALE) formulation is used to write the governing equations in two space dimensions. Maximum cross-flow displacement is observed for Ured = 7 for KC=10. It is found that, the lock-in becomes slightly wider with increase in KC. Different regimes like Initial Branch , Lower Branch and desynchronized have been identified for all KC. Beyond KC = 20, cylinder starts to vibrate with the pulsatile frequency. Moreover, in the Lock-in zone flow amplitude is not always enhanced, and it sometimes gets reduced. This is basically due to state of synchronization between displacement and forcing. For all KCs, in-phase and out-of-phase regimes were also identified for X and Y-direction displacements. Wake width and vortex strength are maximum at the lock-in.