CFD analysis of the near-field vortex dynamics in a confined square jet
As a jet emanates into a confined cavity, it demonstrates a self-oscillating behavior due to the Coanda effect. This paper is focused on a study of the vortex dynamics in the near-field of a starting turbulent square jet before oscillation appears. The jet flows from a submerged square nozzle into a thin rectangular cavity at jet Reynolds number of 54000 based on nozzle hydraulic diameter and average exit velocity. A numerical investigation of the three-dimensional fluid structures in the near-field region is conducted by using an
unsteady Reynolds stress turbulence model with fully developed flow at the inlet. The λ2-criterion vortex
identification method is used to investigate effects of the confinement on the near-field vortex dynamics. Vortex ring evolution and effects of the confinement walls on decay of the vortex rings and the axisswitching is studied. The simulations show that the vortex rings have a square shape near the nozzle exit and that axis-switching occurs at about 0.7 nozzle diameters downstream. Beyond this location the square ring starts to transform to a circular vortex ring at about one diameter and, upon impact with the walls, produces two tornado-like vortices.