Unsteady Fluid Force on Two Tandem Circular Cylinders Subjected to Two-Phase Cross Flow.

Abstract

In this study, we experimentaly examined the characteristics of unsteady fluid forces acting on the downstream cylinder of a two-tandem-cylinder system in the lift direction at P/D=3.0 subjected to two-phase bubble cross flow. The downstream cylinder was oscillated to measure the unsteady fluid force at the frequency (fP) which is a natural frequency of the upstream cylinder in water. Experiments showed the following major results : ( 1 ) At low reduced velocity, we could not observe the differences in the characteristics of unsteady fluid force, that is with respect to void fraction and oscillation amplitude ; ( 2 ) air bubbles decreased the fluid force for the reduced velocity over the value of that in lock-in the state ; ( 3 ) the fluid force was reduced by air bubbles at the void fraction of α≤ 5% for high reduced velocities.