Modal localization in mistuned tube-array structures

Abstract

An investigation of mode localization in mistuned tube-array structures is studied in this work. The continuous action of hot-cold fluid shock waves in tube-array heat exchangers results in a significant abrasive wear of the tubes, which in turn alters their dynamic behavior and may introduce an undesirable modal localization effect within the tube bundle. This study performs a numerical investigation into the problem of modal localization in mistuned tube-array heat exchangers, with cross-flow. In conducting the investigation, the heat exchanger is modeled as a bundle of periodically-arranged cooling tubes in which the vibrational displacements of the individual tubes are weakly coupled to those of their neighbors via a squeezed water film in the gap between them. In general, the numerical results reveal that damage to even a single tube within the array is sufficient to introduce a severe modal localization effect. Furthermore, due to the weak coupling effect of the fluid, the vibrational energy induced by modal localization is confined to the defected tube and its immediate neighbors, and hence the risk of further wear defected within the tube bundle is increased. The results suggest that the modal localization phenomenon is alleviated at higher values of the cross-flow velocity, but becomes more severe as the tube wall thickness is increased.