Simulations of Loosely-Supported Heat Exchanger Tube Bundles Subjected to Fluidelastic Instability Forces

Flow-induced vibration (FIV) is a major concern and is a significant contribution to tube failures in many mechanical components such as heat exchangers and steam generator tube bundles. Therefore, FIV has become an important factor in the design consideration of such devices. Fluidelastic instability (FEI) is the most destructive flow excitation mechanism of FIV in heat exchanger tube arrays subjected to cross fluid flow. Many fluidelastic instability models are based on the linear approach in which only the stability threshold of tubes with ideal supports can be predicted. However, for the purpose of manufacture and to allow for thermal expansion, gaps are permitted between tubes and the supports. This makes the dynamics of these systems highly nonlinear. Therefore, nonlinear models for FEI for a tube in loose supports are required. Several time domain fluidelastic instability models have been devised. The aim of this study is to conduct a comparative investigation of the application of the available time domain models to a problem including support nonlinear behaviour. Hence, impact and friction are regarded as essential aspects in this type of problems. The FEI time domain models are implemented in INDAP (Incremental Nonlinear Dynamic Analysis Program), an in-house finite element code.;Linear simulations were carried out to validate the proposed models. The results were compared with the available experimental data. The comparison showed that in general the four models under consideration were in good agreement with the experimental data. However, the prediction of Lever & Weaver model is less conservative. Numerical computation and analysis of the tube dynamics were carried out to investigate the influence of the clearance on various tube/support interaction parameters such as tube response, impact force, contact ratio and work rate. The results of the nonlinear simulations showed that different levels of the generated work rate were predicted by the four FEI models.