Branching of a horseshoe vortex around surface-mounted rectangular cylinders

Flow visualizations and surface pressure measurements are performed to stud y the branching phenomenon of a horseshoe vortex upstream of a series of re ctangular cylinders with aspect ratios ranging from 0 to 17. The Reynolds n umbers are 500 for visualization experiments and 1990 to 6650 for wind tunn el surface pressure measurements. The flow visualization results indicate t hat a horseshoe vortex will first evolve into a wavy structure and for aspe ct ratios which are equal or larger than 10, the wavy horseshoe vortex will branch itself into smaller regular vortices. The waviness disappears as so on as branching occurs. The number of the branched smaller vortices increas es as the aspect ratio increases further.