Turbulent plane jets: Impingement, instability and interaction with surface gravity waves

For better understanding of the turbulent jet, especially in a wave environment, experiments were conducted in this study to investigate (1) the impingement of the plane jet onto a free surface; (2) the propagation of surface waves in current shear layers generated by the plane jet; (3) the interaction of turbulent plane jet with progressive waves; (4) the coherent structures of turbulent plane jet; and (5) the instability of turbulent plane jet.;In the experiment on wave-current interaction, the wave number was measured with a wave height gauge moving along the wave propagation direction. The waves were measured in an environment of currents, which were generated by the plane jets. In the upstream of the plane jets, the wave number first increases in the velocity-dominated current region and then decreases in the vorticity-dominated current region.;Plane jets in wave environments were observed to have the same flow regimes as in a stagnant ambient, i.e., ZFE, ZEF, ZSI and ZHJ. The self-similar feature in ZEF with a wider spreading of a plane jet was found in a wave environment. Wave-induced velocities u&d15;i, wave-associated mean stresses u&d15;iu&d15; j and wave-induced turbulent Reynolds stresses are r&d15;ij obtained with a phase average scheme. The results show that the wave-induced flow field is dominated by the fundamental mode and the contribution from harmonic is negligible. The amplitude of the fundamental mode of w&d15;,r&d15; ww and r&d15;uu, denoted by w, rˆww and rˆuu and the wave-associated normal mean stress w&d15;w&d15; have similar twin-peak distributions, indicating maximum energy transfer at about half-velocity location eta = +/-0.16. There is an about 180° phase shift across the plane jets for the phase of the fundamental mode of w&d15;,r&d15; ww and r&d15;uu, denoted by qw&d5;, qr&d5; ww and qr&d5;ww .;Coherent vortex structures were observed in the plane jets when the progressive surface waves were imposed, even though no coherent vortex structures are shown in a stagnant ambient. The flow visualizations also show the plane jets are stable for H/d = 130 even though surface waves are imposed.;Experiments on turbulent plane jets impinging onto a free surface in a stagnant ambient at a water depth of H/d = 130 show the existence of four flow regimes in a plane jet: the zone of flow establishment (ZFE), the zone of established flow (ZEF), the zone of surface impingement (ZSI) and the zone of horizontal jet (ZHJ).;Plane jets become unstable to exhibit a flapping motion when the jet exit velocity exceeds a critical velocity W0cr. The flapping frequency f is found to be inversely proportional to the square root of water depth H and the critical jet exit velocity to be linearly proportional to H. (Abstract shortened by UMI.)...