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When it comes to fluid mechanics, Proper Orthogonal Decomposition has often been employed with the intention of building reduced ordered models. In this paper, we rather used POD as a data processing tool for its ability to exhibit "dominant features" of a dynamical system, namely here the vibration of the center tube in a 5x3 square array under cross-flow. Firstly, we conducted numerical simulations at various reduced velocities such that the fluid-structure coupled system was either stable or unstable. The Reynolds number spanned between 300 and 600 (based on gap velocity) so as to avoid unnecessary complexity due to turbulence, since we know that the Fluidelastic Instability can occur even in laminar state. Transpiration Boundary Conditions were applied in order to keep a fully Eulerian formulation, which makes the POD basis calculation much easier. Then, we computed the POD modes from simulations with or without structural motion and compared them from a physical point-of-view. More precisely, we expected that some of the modes display a peculiar behavior when passing across the Fluidelastic Instability.

fluidelastic instability ; POD ; tube bundles