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