Effects of Flow Velocity Fluctuation around Excited Cylinder on Cylinder Oscillation.

Abstract

A study was performed to characterize the behavior of the flow moving past an oscillating circular cylinder and the interactions between the flow velocity fluctuation and the cylinder oscillation. The oscillations of the cylinder had three distinct regions : two instability regions separated by a stability region. The flow velocity fluctuation was measured using built-in electromagnetic flow meters. The velocity data showed that the flow velocity fluctuations : a) had two frequency components in both the stability region and the second instability region ; the first dominant frequency matched the dominant frequency of the in-line oscillation and the second dominant frequency was induced by the alternate vortices. b) had phase estimations that : 1) indicated the effect of the alternate vortices on the cylinder gave different timings for the stability region and the second instability region. 2) confirmed the energy transfer between the flow and the cylinder occurred at the dominant frequency of the in-line cylinder oscillations. 3) indicated the flow velocity fluctuations induced by the alternate vortices were the antiphase at the opposite of the cylinder and 4) showed the flow velocity fluctuation at the dominant frequency of the in-line oscillation was stable for the two instability regions and unstable for the stability region.