Three-dimensional large-scale and very-large-scale coherent structures in a turbulent axisymmetric jet

The direct numerical simulation database from Shin et al. ( J. Fluid Mech. , vol. 823, 2017, pp. 1–25) is used to study three-dimensional vortical and very-large-scale coherent structures in a turbulent round jet at Reynolds number of $7300$ . In particular, horseshoe vortices their role the formation near intermediate fields are assessed. swirling strength criterion together with conditional averaging visualize volumetric structures. It shown that, similar wall-bounded flows, populated symmetric asymmetric horseshoe-like vortices, which induce high-momentum low-momentum regions flow. However, unlike what found for inverse common jet. They prevail shear region around potential core field contribute mixing field, groups axially aligned long streaky structures, periodic azimuthal streamwise directions. motions (VLSMs) consisting regions, flanked on either side by be associated vortices. Instantaneous flow suggest that tend concatenate form organized spiral as well VLSMs. A detection scheme introduced identify average over these This reveals VLSMs constitute $72\,\%$ $28\,\%$ total VLSMs, respectively.