Vortex excitation caused by longitudinal vortices shedding from cruciform cylinder system in water flow

Abstract

Wind tunnel experiments by the present authors have shown that a large crossflow oscillation can be induced on the upstream cylinder in cruciform cylinder system by two types of longitudinal vortices, i.e. trailing and necklace vortices. In this study, experiments on this phenomenon are carried out in a water tunnel over a Reynolds number range comparable with that of the wind tunnel experiments to investigate the effects of the mass ratio MR and the Scruton number S c. The alternating lift coefficient CLR for Kármán vortex excitation in water flow agrees well with that in air flow in spite of the large differences in MR and S c between them. However, the value of CLR for the trailing vortex excitation is much lower in water flow and no definite excitation due to the necklace vortex is observed.