Vibrations of two circular cylinders in tandem subjected to two-phase bubble cross flows

Abstract

This paper deals experimentally with the effect of air bubbles on the vibration of two circular cylinders installed in tandem with a pitch-to-diameter ratio of 3. Experiments were done changing the void fraction from 0% to about 20% for each reduced velocity ranging from 0.5 to 8; vibrational accelerations were measured in both the lift and drag directions for each cylinder. The experiments revealed that (i) the vibration of the two-cylinder tandem system was excited by air bubbles in the flow for small reduced velocities, (ii) a small amount of air bubbles equivalent to about 4% of the void fraction suppressed the strong, out-of-phase vibration in the downstream cylinder when the reduced velocity was about 7, and (iii) the vibration suppression was likely due to the entrainment of air bubbles in the wake region behind the upstream cylinder.