Etude des forces dues a la turbulence dans un ecoulement diphasique transverse sur un faisceau de tubes en configuration triangulaire tournee

Two-phase cross-flow exists in many shell-and-tube heat exchangers. The associated flow-induced excitation forces can cause tube motion that can result in long-term fretting wear or fatigue.;An experimental program was undertaken with a rotated-triangular array of cylinders subjected to air-water cross-flow, to simulate two-phase mixtures. The tube bundle here has the same geometry as that of a real steam generator. The quasi-periodic forces have now also been observed in this tube bundle. The project aims to understand the turbulence induced forces on a tube bundle subjected to two-phase cross-flow. In order to be able to measure correctly the force spectra, force measurements on the tubes having a smaller diameter required an appropriate design for the test section and the instrumented tubes.;Data on drag and lift dynamic force spectra are provided in this project. The variations of rms forces with the mass flux and of the mean frequencies with the flow velocity are also investigated. Data on the effect of the position of the tubes in the tube bundle are provided, and so are the spatial force correlations. Comparisons are also made with previous studies on the subject.;A detailed study on the shape of the dynamic force spectra leads to a new scaling procedure for collapsing dimensionless equivalent power spectral densities and dimensionless frequency.;Detailed flow and vibration excitation force measurements in tube bundles subjected to two-phase cross-flow are required to understand the underlying vibration excitation mechanisms. Studies have already been done on the subject, providing data on flow regimes, fluidelastic instabilities and flow-induced turbulence. However, the force spectra data remain very scarce. The spectra have also generally been supposed to be relatively flat. A recent study, performed with tubes having a larger diameter than that in an actual steam generator, showed the existence of unexpected quasi-periodic forces in two-phase cross-flow.;The shape of the obtained spectra is very different from those obtained in single-phase cross-flow. This suggests that random forces in two-phase flow are generated by a different mechanism than the flow fluctuations as in single-phase flow. A simple model is developed assuming that the forces are generated by the "impacts" of the two different phases in contact with the tube.