Heat exchangers are massive structures of tube bundles subject to cross-flow which induces potentially high amplitude vibrations. The most damaging mechanism is the fluidelastic instability (FEI). Beyond a critical velocity of the fluid, the fluidelastic forces have a destabilizing effect leading to the FEI.
The aim of this study is to simulate such an instability in an array of thousands of tubes. Direct solving of the Navier-Stokes equations is too costly for the current computational power. A more reasonable approach consists in averaging the fluid and solid equations on a control volume introducing a porosity function. The averaging process introduces new unknowns. As a consequence, new closure relations modeling the fluid-structure interactions need to be defined.