On dynamics and secondary currents in meandering confined turbulent shallow jet

• Intense secondary currents are observed in a shallow turbulent wall-bounded jet.
• Typical smaller scale coherent structure is a vortex tube oriented along the flow.
• The near field contains a peak of mean streamwise vorticity where the strongest entrainment is observed.
• In the far field the described long streamwise rolls meander together with the flapping jet core.

We study a shallow turbulent confined jet issuing from a wide duct of the aspect ratio around 0.1 (≈H:B=≈H:B= height: width) into a large rectangular reservoir (200H×267H200H×267H long in spanwise and streamwise direction) bounded by two parallel plates with the distance H   using a wall-resolved Large-eddy simulation. According to statistical and dynamical features of the flow the domain is divided into the near (<40H≈4B<40H≈4B), middle and far (>130H≈13B>130H≈13B) field along the streamwise coordinate. The well-known meandering (or flapping) motion of the jet core starts at ≈5B≈5B generating large-scale planar vortices similar to the von Kármán vortex street. We find that the typical smaller scale coherent structure appears to be a vortex tube (with the cross-section diameter