Experimental investigation on the transition of separation/attachment in steady laminar juncture flows

The topological structure and the “separation/attachment” transition of the outermost singular point in steady laminar juncture flows are investigated. The detailed experimentation is conducted using particle-image-velocimetry-based quantitative technique in a water channel. The experimental results reveal that the outermost attachment topology can exist in various horseshoe vortex systems that contain zero to three primary vortices. The parametric study has two major elements: the obstacle bluntness factor and the ratio of the boundary layer thickness to the obstacle width. The outermost topology in the symmetry plane transforms from attachment (half node) to separation (half saddle) as the obstacle bluntness increases or the ratio of the boundary layer thickness to the obstacle width decreases. It is also observed that the flow has a tendency to reattach to the body-fitted surface as it sweeps by the sides of an obstacle, even if the outermost singular point is a separation half saddle in the symmetry plane.