Three-dimensional flow structure of a non-buoyant jet in a wave-current coexisting environment

The three-dimensional flow structure of a non-buoyant vertical round jet in a wave-current coexisting environment is investigated. Laboratory experiments are first conducted to measure instantaneous flow patterns and mean velocity fields of the jet in a wave-current coexisting environment and a current-only environment for comparison. The distinctive 'effluent clouds' phenomenon is clearly observed in the wave-current coexisting environment but scarcely observed in the current-only environment. Moreover, the mean velocity vectors bend further toward the bottom when the wave effect is present. To reveal a more detailed flow structure of the jet in the wave-current coexisting environment, a large eddy simulation (LES) model is developed and validated against the experimental data. The mechanisms of formation and development of 'effluent clouds' are unravelled based on in-depth analysis of the vorticity contours and the high-pass filtered flow fields on the vertical symmetrical plane. With the variation of instantaneous jet-to-current velocity ratio, the 'effluent clouds' dynamically interact with the current-induced counter-rotating vortex pair (CVP), resulting in an inverted pear-shaped distribution of mean flow field above the CVP structure centre. This study highlights that the existence of 'effluent clouds' can lead to a significant enhancement of jet spread and dilution in the wave-current coexisting environment.