Generation and evolution characteristics of the mushroom-like vortex generated by a submerged round laminar jet

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 t*(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.