Experiments on vortex dipoles generated by a submerged round jet

The formation mechanism and evolution characteristics of a submerged round jet in a uniform fluid of finite depth are investigated experimentally. A spillover system is designed to produce a continuous horizontal jet in the background fluid with a constant velocity, and the flow is visualized by the dyed liquid. Experiments are conducted under different combinations of Reynolds number Re, confinement number C and nondimensional draft d/H, where d is the vertical distance from the jet to the free surface, and H is the depth of the ambient fluid. Four flow patterns are identified for various C. When C1, the jet shows a deep-water pattern, while for 1 C2, it shows the transitional pattern, the jets do not develop a structured flow for the two jet patterns. When 2 C10, the jet shows the shallow-water pattern, while if C10, the jet shows the extreme-shallow-water pattern. In both these two patterns, the jets generate vortex dipole structures. In the extreme-shallow water pattern, the nondimensional vortex formation time tf* for the vortex dipole structure is proportional to the nondimensional injection time Tinj* for various draft d/H. In the shallow-water pattern, tf* depends linearly on Tinj*Re1/2 when the draft d/H=0.5; however, there is no observable relationships between tf* and Tinj* for other draft d/H.