Universality of Longitudinal Vortices Shedding from a Cruciform Two Circular Cylinder System in Uniform Flow

Earlier wind tunnel experiments supported by visualization in water flow carried out by the present authors showed that two types of longitudinal vortices shed periodically from a cruciform two identical circular cylinder system in uniform flow. These longitudinal vortices induce resonance-like oscillations over a wide velocity range accompanied by the synchronization phenomenon. The specific aim of this work is to investigate the universality of the longitudinal vortex shedding by carrying out experiments in both water and air flows. In addition to the velocity, the alternating lift force loading on the upstream cylinder in water flow is measured by using load-cells. The two longitudinal vortices are confirmed to shed periodically for small size systems in water flow in spite of large difference in the experimental conditions. Relationships of the Strouhal number and the lift force coefficient for the vortex shedding against Reynolds number agree well with the previous data except for the peculiar vanishing of the necklace vortex when Re is larger than 22000. The cause of this phenomenon is left for further investigation.