Influence of gap between two cylinders set in cruciform arrangement on Karman vortex excitation and longitudinal vortex excitation

Karman vortex excitation can be suppressed by setting a rectangular cylinder in the wake. However, one kind of the longitudinal vortices, Trailing vortex or Necklace vortex, sheds periodically near cruciform two cylinders arrangement in a certain conditions about free stream velocity, gap between the cylinders and rectangular cylinder width. The longitudinal vortex induce stronger vortex excitation compared with Karman vortex excitation. The influence of these parameters on Karman vortex excitation and longitudinal vortex excitation was clarified by wind tunnel experiment. The flow condition that neither Karman vortex excitation nor the longitudinal vortex excitation did not happen was found by this research.