Experiments and computations of a loosely supported tube in a rigid bundle subjected to single-phase flow

In this paper the problem of computing the nonlinear vibro-impact responses of loosely supported heat-exchanger tubes subjected to fluidelastic coupling forces, as well as to the turbulence excitation from transverse flows, is addressed. Emphasis is on the fluidelastic modeling within a time domain nonlinear framework, as well as on the stabilizing effect of impacts on the fluidelastic coupling forces. Theoretical computations of the linear and vibro-impacting regimes of a flow-excited flexible cantilever test tube, within a rigid 3×5 square bundle, are based on the experimentally identified fluidelastic coupling force coefficients and turbulence spectrum. Computations are then compared with the experimental vibratory responses, enabling a full validation of the modeling approach. Furthermore, interesting conclusions are drawn, concerning (a) the energy balance between sources and sinks, for a vibro-impacting tube subjected to fluidelastic forces and (b) the dependence of the vibration response frequency on impacts at the loose supports, and their effect on the nonlinear restabilization of fluidelastically unstable tubes. Details on the following aspects are reported in the paper: (1) numerical modeling of the fluidelastic coupling forces for the time domain computations; (2) experimental identification of the fluidelastic coupling coefficients; (3) computations and experiments of both linear and vibro-impacting responses under the combined action of turbulence and fluidelastic coupling and (4) energy aspects of the vibro-impacting fluidelastically coupled tube responses.