The flow around two identical circular cylinders, arranged in configurations where
one of the cylinders is immersed in the wake of the other, is studied using numerical
simulations. Two aspects of such flows were considered. The first is the stability
of nominally two-dimensional time-periodic wakes to three-dimensional perturbations.
We investigated flows around tandem and staggered arrangements with
diverse centre-to-centre distances. Direct stability analysis and numerical simulations
were employed, and the results are compared to those obtained for the flow
around an isolated cylinder. The onsets of the three-dimensional instabilities were
calculated and the unstable modes are fully described. In addition, we assess the
nonlinear character of the bifurcations and physical mechanisms are proposed to
explain the instabilities. The second aspect considered in this thesis is the flowinduced
vibration experienced by a rigid cylinder when it is mounted on an elastic
base and immersed in the wake of a fixed identical cylinder. Tandem arrangements
with centre-to-centre distances varying from 1.5 to 8 cylinder diameters were tested.
The flow was simulated using an Arbitrary Lagrangian-Eulerian approach that coupled
the solution of the structure equations with that of the flow. Two- and three- dimensional
simulations were performed to assess the mutual influence between the
three-dimensional flow structures in the wake and the motion of the cylinder. The
response of the downstream cylinder is compared to that of an elastically-mounted
rigid isolated cylinder. Based on the simulation results we propose physical mechanisms
to explain the origin of the excitation.