Investigation on streamwise fluidelastic instability of rotated triangular tube bundles subjected to two-phase cross-flow

Streamwise fluidelastic instability of rotated triangular tube array subjected to air-water cross-flow is investigated in this paper. Critical velocity of fluidelastic instability was measured only from 0% to 30% void fraction because the tube bundles were destroyed at 30% void fraction. One type of streamwise fluidelastic instability called coupling instability was observed. As further study, damping ratio of two-phase and hydrodynamic mass of tube bundle both in transverse and streamwise directions were measured from 0% to 80% void fraction. The results suggest that, tube will destroy first in the direction with small stiffness if coupling instability occurs. The damping ratio in streamwise direction is greater than that of transverse direction at the same void fraction. With increasing of void fraction, the damping ratio increases first and then decreases. Fluidelastic instability constant K in transverse direction is 5.3, and the K in streamwise direction is 17.6 below 30% void fraction.