Effects of upstream tetrahedron length on flow characteristics around juncture of circular cylinder and flat plate

The influences of the length of tetrahedron juncture flow controller (JFC) and Reynolds number on the flow in the vertical symmetrical plane of the upstream region and near wake of a circular cylinder-flat plate juncture were studied experimentally in a towing water tank. The flow was analyzed by the particle-tracking flow visualization method and particle image velocimetry. The Reynolds number ranged from 500 to 6000. The inverse of nondimensional boundary-layer displacement thickness was from 3.27 to 10.33. The tetrahedron length-to-circular cylinder diameter ratio ranged from 0 to 1.4. The natural flow presented single-vortex, dual-vortex, triple-vortex, and unsteady vortical flow modes in different ranges of Reynolds numbers. The effects of the tetrahedron JFC installed at the leading edge of the juncture on the flow patterns significantly depended on the tetrahedron length and a little on the Reynolds number. Larger tetrahedron length was required to change flow modes and eliminate horseshoe vortices at larger Reynolds number. Within the range of Reynolds numbers <6000, the tetrahedron length-to-cylinder diameter ratio must be larger than about 1, so all flows near the upstream region of the juncture directed forward without reversal or vortices. The tetrahedron JFC significantly reduced the wall shear stress in the near wake of the juncture when compared with that of the natural flow.