Abstract
Instantaneous three-dimensional velocity fields in the wake of a hemisphere located on an open channel bed are measured by using flow visualization in multi-section and Mass-Consistent model. Instantaneous three-dimensional forms of the coherent structure at high Reynolds number are shown by three-dimensional vorticity vectors. The large vortex in the wake is similar to the hairpin vortex, which can be observed in a hemisphere wake at low Reynolds number. However, the long legs of hairpin in the streamwise direction at low Reynolds number are not observed. The secondary hairpin vortex has been generated on the upstream side of the large hairpin vortex and coalesced into the large hairpin. The instantaneous pictures of the coherent structure are taken at short time interval and their behaviors are investigated. The flow patterns induced by the large hairpin vortices are also examined.
