Modelling of fluidelastic instability in a square inline tube array including the boundary layer effect Burns Anderson a , Marwan Hassan a , Atef Mohany b,n a School of Engineering, University of Guelph, Guelph, Canada b Faculty of Engineering and Applied Science, University of Ontario Institute of Technology, Oshawa, Canada article info Article history: Received 22 February 2013 Accepted 17 March 2014 Keywords: Fluidelastic instability Time-domain modelling Unsteady boundary layer Flow-induced vibrations Tube arrays abstract Flow-induced vibration (FIV) is a design concern in many engineering applications such as tube bundles in heat exchangers. When FIV materializes, it often results in fatigue and/or fretting wear of the tubes, leading to their failure. Three cross-flow excitation mechanisms are responsible for such failures: random turbulence excitation, Strouhal periodicity, and fluidelastic instability. Of these three mechanisms, fluidelastic instability has the greatest potential for destruction. Because of this, a large amount of research has been conducted to understand and predict this mechanism. This paper presents a time domain model to predict the fluidelastic instability forces in a tube array. The proposed model accounts for temporal variations in the flow separation. The unsteady boundary layer is solved numerically and coupled with the structure model and the far field flow model. It is found that including the boundary layer effect results in a lower stability threshold. This is primarily due to a larger fluidelastic force effect on the tube. The increase in the fluidelastic effect is attributed to the phase difference between the boundary layer separation point motion and the tube motion. It is also observed that a non-linear limit cycle is predicted by the proposed model. & 2014 Elsevier Ltd. All rights reserved. 1. Introduction Historically, heat exchangers have been among the most failure prone components in nuclear power plants (Diercks et al., 1996) and continue to be a major reliability issue as evident by recent tube degradation problems (e.g. Units 2 and 3 of the San Onofre Nuclear Generating Station, Unit 1 of Three Mile Island, Unit 1 of Arkansas Nuclear One). Most of the tube failures are due to corrosion, fatigue and fretting wear of the tubes. Fatigue and fretting wear are a result of dynamic loading caused by three cross-flow excitation mechanisms: turbulent buffeting, Strouhal periodicity and fluidelastic instability (FEI) (Weaver and Fitzpatrick, 1988). The turbulent buffeting mechanism results in long-term failures due to fretting-wear damage at the tube supports, while Strouhal periodicity and fluidelastic instability result in short-term failures due to excessive vibration of the tubes. Of the three mechanisms, FEI has the greatest potential for destruction in heat exchanger tube bundles. Because of this, a large amount of research has been conducted to characterize this mechanism. FEI is a self excitation mechanism caused by the interaction of the flexible tubes and the fluid forces. The motion of the tubes alters the flow field which, in turn, creates fluid forces that further excite the tube. Energy is thereby transferred from the flow to the tube. Problems arise when more energy is extracted from the fluid flow than can possibly be dissipated by Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/jfs Journal of Fluids and Structures http://dx.doi.org/10.1016/j.jfluidstructs.2014.03.003 0889-9746/& 2014 Elsevier Ltd. All rights reserved. n Corresponding author. E-mail address: atef.mohany@uoit.ca (A. Mohany). Journal of Fluids and Structures ] (]]]]) ]]]–]]] Please cite this article as: Anderson, B., et al., Modelling of fluidelastic instability in a square inline tube array including the boundary layer effect. Journal of Fluids and Structures (2014), http://dx.doi.org/10.1016/j.jfluidstructs.2014.03.003i