The evolution mechanism and characteristics of the submerged laminar round jet in a viscous homogenous shallow water layer are investigated through computational modeling. The laminar mode is used to solve the Navier-Stokes equations. In order to visualize the formation and evolution of the flow pattern, the volume of fluid(VOF) method is adopted to simulate the free surface of the water layer below the air and to trace the jet fluid. The results show that the jet forms a class of quasi-two-dimensional(Q2D) vortex structures in the ambient fluid with unequal influence from the bottom wall and free surface. The time dependence of three parameters,defined for the flow pattern as jet length, spiral radius and pattern length, is investigated quantitatively in their non-dimensional forms. Three different Reynolds numbers and two injection durations are further considered to discuss their influence on the flow pattern.
This paper studies the formation mechanism and the evolution characteristics of the mushroom-like vortex generated by a submerged laminar round jet based on experiments, CFD simulation and a theoretical model. The results of the numerical simulations agree well with those obtained by the experiments, and three distinct stages are identified in the formation and evolution processes of the mushroom-like vortex： the starting, developing and decaying stages. Three non-dimensional parameters for such a mushroom-like vortex： the length of the jet L＊, the vortex radius R＊ and the circulation length d＊, are introduced, and the variation characteristics of these parameters with respect to the non-dimensional time t＊ are quantitatively analyzed. In the starting stage, L＊ and d＊ increase linearly with t＊ while R＊ approximately remains a constant. In the developing stage, a considerable self-similarity is observed, and L＊, R＊, d＊ have the same proportional relationship with respect to 1.1/2 regardless of the variations of the Reynolds number and the injection duration time. In the decaying stage, L＊ and R＊ are approximately proportional to t＊1/5, while d＊ nearly levels off at a constant. Furthermore, a theoretical model is proposed for the time evolution characteristics of the jet length, with predictions in good agreements with numerical and experimental results.
