圆管潜射流生成偶极子涡特性实验

利用溢流恒压装置产生具有稳定出流速度的圆管潜射流, 结合染色液流态显示方法, 在多种射流无量纲潜深d/H、雷诺数Re以及限制数C的组合下, 实验研究了该潜射流动量在有限深密度均匀流体中的演化特性, 其中d为射流潜深, H为水深. 研究表明, 当C<1时潜射流表现为深水特征, 而当1≤ C<2时潜射流表现为过渡特征, 在这两种情况下均不产生任何形式的大尺度相干结构; 当2≤ C<10时潜射流表现为浅水特征, 而C≥10时潜射流表现为极浅水特征, 在这两种情况下均产生大尺度的偶极子涡结构. 对极浅水特征潜射流, 在各种无量纲潜深下, 偶极子涡结构的无量纲形成时间t_f^*与无量纲射流时间T_inj^*均满足相同的正比例关系; 对浅水特征潜射流, 当d/H=0.5时, t_f^*与T_inj^*满足某种线性关系, 但对其他无量纲潜深, t_f^*与T_inj^*之间无明显规律.关键词：圆管潜射流限制数偶极子涡结构形成时间

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 C<1, the jet shows a deep-water pattern, while for 1≤ C<2, it shows the transitional pattern, the jets do not develop a structured flow for the two jet patterns. When 2≤ C<10, the jet shows the shallow-water pattern, while if C≥10, 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 t_f^* for the vortex dipole structure is proportional to the nondimensional injection time T_inj^* for various draft d/H. In the shallow-water pattern, t_f^* depends linearly on T_inj^*Re^1/2 when the draft d/H=0.5; however, there is no observable relationships between t_f^* and T_inj^* for other draft d/H.
Keywords：submerged round jetconfinement numbervortex dipoleformation time