Vortex shedding patterns, their competition, and chaos in flow past inline oscillating rectangular cylinders

Abstract

The flow past inline oscillating rectangular cylinders is studied numerically at a Reynolds number representative of two-dimensional flow. A symmetric mode, known as S-II, consisting of a pair of oppositely-signed vortices on each side, observed recently in experiments, is obtained computationally. A new symmetric mode, named here as S-III, is also found. At low oscillation amplitudes, the vortex shedding pattern transitions from antisymmetric to symmetric smoothly via a regime of intermediate phase. At higher amplitudes, this intermediate regime is chaotic. The finding of chaos extends and complements the recent work of Perdikaris et al. [1]. Moreover it shows that the chaos results from a competition between antisymmetric and symmetric shedding modes. Rectangular cylinders rather than square are seen to facilitate these observations. A global, and very reliable, measure is used to establish the existence of chaos.

Numerical simulation of flow past an 8:1 oscillating rectangular cylinder at Re = 22 000

“…In general, for inline excitations, the average component of the excitation favors the antisymmetric vortex shedding mode, while the oscillating component promotes the symmetric vortex shedding mode. These two mechanisms may compete with each other, leading to pattern competition and chaos (Perdikaris et al 2009, Srikanth et al 2011. Srikanth et al (2011) investigated the effect of incoming oscillatory flow on square and rectangular cylinders (L/D = 0.125, 0.25, 0.5 and 1, fr = 1.0-4.0) at Re = 200.…”

“…These two mechanisms may compete with each other, leading to pattern competition and chaos (Perdikaris et al 2009, Srikanth et al 2011. Srikanth et al (2011) investigated the effect of incoming oscillatory flow on square and rectangular cylinders (L/D = 0.125, 0.25, 0.5 and 1, fr = 1.0-4.0) at Re = 200. The chaotic vortex shedding is attributed to mode competition, where the transition from antisymmetric to symmetric shedding is marked by chaotic shedding with the vortex shedding frequency changing while keeping all other parameters constant.…”

“…Besides, it is essential to consider the effect of solid structure oscillation in the passive and active control schemes based on surface pressure or near-wall velocity. Srikanth et al (2011) simulated two-dimensional flow past an inline oscillating rectangular cylinder (L/D = 0.125, 0.25, 0.5 and 1, fr = 1.0-4.0) The simulation results indicated that the vortex shedding mode changed with the increase of cylinder oscillation frequency. At higher oscillating amplitude A/D = 0.175, the transition of the vortex shedding mode from antisymmetric to symmetric became chaotic.…”