EXPERIMENTAL INVESTIGATION OF OUT-OF-FLOW FLUIDELASTIC INSTABILITY FOR ROTATED TRIANGULAR TUBE BUNDLES SUBJECTED TO SINGLE-PHASE AND TWO-PHASE TRANSVERSE FLOWS
Résumé
An experimental program is conducted to study the vibration response of a rotated triangular tube bundle with a pitch ratio of 1.44 and an aspect ratio of 10. The tube bundle is subject to a single-phase (air or water) or a two-phase air-water cross-flow, with an homogeneous void fraction in the range [0.1,0.95]. The bundle is free to vibrate only in the out-of-flow, i.e. lift direction. Four bundle configurations, with one or multiple flexible tubes, are tested by increasing the flow velocity up to the onset of a fluidelastic instability. We show that a bundle with a single flexible tube is unstable only for homogeneous void fractions smaller than 0.3. A bundle with multiple flexible tubes is shown to be unstable for all void fractions. A modal analysis also shows that high order modes, i.e. modes with at least two degrees of freedom, are necessary to observe an instability for void fractions greater than 0.3. Finally, we show that the instability is characterized by a Connors's constant greater than the one generally observed in the literature.