STREAK-EJECTIONS UNDER SHEARED AIR-WATER INTERFACE
水-气界面下低速流体条带的喷射行为

Described in this paper are careful visual and quantitative studies on ejection phenom-ena of low-speed streaks under sheared air-water interface. During an ejection process, a portion oflow-speed streaks rapidly migrates away from the water surface, and subsequeatly breaks down ina violent interaction with faster flow, demonstrating that such processes play an important role inthe turbulent transport between the interface and deeper layers. Quantitative data derived fromflow-visualization pictures reveals fundamental features in ejection events, including frequency,trajectories and velocities of ejected fluid. Comparisons of these findings with the correspondingfeatures of near-wall streak-ejections are also made. Temporal distributions of ejection and burstingevents, together with the visual observations, indicateo that a burst may involve either a single ejec-tion or multiple ejections closely grouped together, and the time interval between ejection events isgenerally much less than that between bursts. Furthermore, the occurrence of both ejections andbursts exhibits intense randomness. The comparison of a turbulence production profile with thecorresponding frequency distribution of ejections is presented. The remarkable agreement in theshape of two curves strongly suggests that ejection processes is the chief contributor of turbulentkinetic energy.