Narrow Results

Although the flapping oscillatory motion is organized, its effect on the mean flows of turbulent plane jets is similar to the effect of turbulence. Therefore, the close relation for the stress due to flapping-induced velocity components is assumed to be similar to the relation for the turbulent Reynolds stress, and the similarity theory applicable for mean flows of turbulent plane jets is extended to that of unstable flapping turbulent plane jets. The results show the effect of flapping motion on mean flows can be regarded as two folds: one is to enhance the mixing by flapping-induced Reynolds stress and the other is to modify the effective advection. The results from similarity analyses are in good agreement with the experimental data.

Based on volume of fluid (VOF) technique, the flapping motion of submerged turbulent plane jet in shallow water impinging vertically onto the free water surface was simulated. To study further on the flapping motion, the power spectrum density, the centerline velocity decay, as well as the mean velocity profiles of the jet were all investigated in this paper. The results are in great agreement with those of theoretical analyses, and the results show that the flapping motion is a new flow pattern of submerged turbulent plane jets.

In order to study the effect of wall on the flow pattern of a submerged turbulent water jet in narrow channels, the flow field was visualized by a laser-induced fluorescence (LIF) system at different Reynolds numbers. Those images showed that flow motion in a narrow channel is different from that of a turbulent plane jet without narrow channels. There are three flow patterns in narrow channels: stable impinging, stable jet with recirculation vortices and flapping turbulent jet.