This study employs large-eddy simulation to investigate turbulent structures of a planar offset jet characterized by an offset ratio of 5 and a Reynolds number of 7500. A combined diagnostic methodology based on proper orthogonal decomposition (POD), quadrant analysis, and vortex-core-based conditional averaging is used to examine the spatial properties of ejection and sweep events, their contributions to Reynolds shear stress, and their relationship with vortex structures in the present case. POD results reveal that, across most shear layers, the energy-containing and large-scale structures predominantly exhibit extensive ejection or sweep events. Quadrant analysis shows a clear mismatch between the occurrence frequency of ejection and sweep events and their contributions to Reynolds shear stress in the outer shear layers of the pre-attachment and wall jet regions: the more frequently occurring event type does not necessarily make the larger contribution to Reynolds shear stress. However, this mismatch becomes weaker in the inner shear layer of the pre-attachment region, under the influence of the recirculation region, and is largely suppressed in the inner shear layer of the wall jet region, due to the strong near-wall confinement. The vortex-core-based conditional statistics further indicate that the observed frequency-contribution mismatch stems from an imbalance in intensity between vortex-induced ejection and sweep events. The present study, through a combined diagnostic methodology, further deepens the understanding of turbulent structures and the generation mechanisms of Reynolds shear stress within offset-jet shear layers, providing a theoretical reference for understanding pollutant transport, diffusion, and desalination processes under such flow conditions.
Jiang et al. (Mon,) studied this question.