Competition between Turbulence and Fluid-Elastic Forces in the Response of a Loosely Supported Tube under Cross-Flow

In some degraded situations of heat-exchangers, tubes may be loosely supported while subjected to intense cross-flow generating both turbulence and fluid-elastic forces, and so have vibro-impacting responses. This paper aims at providing a better understanding of the dynamics of such systems in which the conjunction of stops with gaps, broadband random excitation, and fluid-elastic coupling forces, either stabilizing or destabilizing, produces some rather amazing effects linked to a general capacity for the system to be auto-adjusted by the impacts. It is especially shown, (i) how a non-linear gap-system 'escapes from instability' by reinforcing the sequence of impacts, (ii) the almost perfect time-history mirror symmetry between the works of turbulence and fluid-elastic forces in the energy balance; (iii) the dissipative aspect of turbulence in some cases. Moreover the paper deals with the relative weight of turbulence and fluid-elastic forces in the tube response that notably depends on the gap size. For this, turbulence is considered as a perturbation of limit cycles obtained when the fluid-elastic forces are the only acting fluid-forces. The study is based on configurations mainly 1-DOF, like the one that has been experimentally tested, but extrapolations for real tube bundle are evoked in conclusion. (authors)