Wake of an Oscillating Cylinder in Noisy Flow

The wake of a circular cylinder executing undamped transverse vortex-induced vibrations in stochastic noisy flow is numerically analyzed at Reynolds number, Re = 150. The mass ratio (m*) of the cylinder is 2 and the range of reduced speed (U*) is between 1 and 15. A Gaussian noise is added to mean flow velocity at the inlet and the computations are performed using a discrete forcing Immersed Boundary Method (IBM) based in-house fluid flow solver. The vortex-shedding and arrangement of vortices near and away from the oscillating structure is analysed for various values of U* in pre-synchronization, synchronization and post-synchronization zones of the cylinder vibration. For an interesting case in the synchronized zone (U* = 4), in the region close to the cylinder surface, the number of vortices shed in each oscillation cycle is different. Another important observation was the absence of vortex-shedding for certain oscillation cycles. Unlike the vibrations under a uniform flow field at the inlet, the arrangement of vortices in the noisy inflow are highly dynamic and standard modes of vortex shedding are not always recognised. However, in the farwake, rich vortex interaction behaviour like vortex-merging, vortex-pairing and vortex breakdown are observed.