Experimental Investigation on Juncture Flow Associated with a Surface-Mounted Circular Cylinder Trailed by a Backward-Facing Step

Juncture flows associated with surface-mounted obstacles can be characterized by a U-shaped tubular vortical flow known as horseshoe vortex (HSV). Horseshoe vortices are usually detrimental to engineering applications. In order identify boundary geometry that may effectively reduce HSV’s strength for further design of HSV-reduction devices, or otherwise enhance it disaster prevention avoiding such in design, the characteristics HSVs influenced external geometries must first understood. Thus, we experimentally investigated juncture field fundamental geometry—a circular cylinder mounted perpendicular plane surface—with trailing backward-facing step (BFS) representing novel idea downstream effects on upstream-formed structures. This setup is not only one simplest nonplanar generates features an unsteady separated shear layer considerably affect HSV, but also new attempt without prior knowledge. We used particle image velocimetry (PIV) and PIV-based visualization techniques combined vortex-fitting algorithm measure HSV its kinematic modes at low Reynolds number 1166. observed from flow-visualization results regarding their duration percentages follows: (1) BFS: “oscillation small displacement” (98.6%) “breakaway roll-up” (1.4%); (2) BFS (step height/cylinder diameter = 1.5): (83.3%), “merging” (4.5%), “mixed” (12.2%). It clearly evident increased complexity modes, i.e., unsteadiness HSV. Moreover, PIV show reduced stretching, which resulted 8.24% circulation 6.37%, was enhanced BFS.