Modeling of Fluidelastic Instability Forces in Fully Flexible Tube Arrays

Fluidelastic instability remains the most devastating phenomenon in tube bundles subjected to cross-flow. Models have been developed to estimate the threshold of instability. Moreover, several time-domain models of fluidelastic instability have been developed to determine tube/support interaction parameters of tubes with loose supports. The present work deals with time domain modeling of fluid-elastic instability forces in a fully flexible tube array subjected to cross-flow. The model is based on the flow redistribution theory proposed initially by Lever and Weaver [1]. The proposed model utilizes fewer input parameters and can model various tube bundle geometries with any pitch-to-diameter ratio. Finite element method is used for solving the system response. The flow field inside the tube array is discretized into flow subdomains, each of which is surrounded by 4 tubes. The perturbation in the flow field, within each subdomain, is obtained by superimposing the effects of neighboring tube motions. The model has been applied to assess the response of a single flexible tube as well as multiple flexible tubes. It is shown that the single flexible model overestimates the stability threshold compared to the multiple flexible tube counterpart, especially at high mass-damping parameters. The results show a good agreement between the predicted and the experimental results. The proposed model does not assume any predetermined tube response or any tube motion pattern.