Abstract
Flow around large roughness elements in open channel flow is studied by flow visualization using hemisphere and hemicylinder in a flow. When water depth to roughness height ratio (H/R) equals 3, shed vortices reach the water surface and there occurs ‘boiling phenomenon’. The flow around a two-dimensional roughness (hemicylinder) was found similar to that of the hemisphere, and boiling phenomenon appeared in 5 rows. Near the reattachment point, the mean flow is upward in the “vortices head's” section and downward in the “leg's” section. Results show the effect of vortices' motion on the mean velocity profile.
