Proper orthogonal decomposition analysis of coherent motions in a turbulent annular jet

A three-dimensional incompressible annular jet is simulated by the large eddy simulation (LES) method at a Reynolds number Re = 8 500. The time-averaged velocity field shows an asymmetric wake behind the central bluff-body although the flow geometry is symmetric. The proper orthogonal decomposition (POD) analysis of the velocity fluctuation vectors is conducted to study the flow dynamics of the wake flow. The distribution of turbulent kinetic energy across the three-dimensional POD modes shows that the first four eigenmodes each capture more than 1% of the turbulent kinetic energy, and hence their impact on the wake dynamics is studied. The results demonstrate that the asymmetric mean flow in the near-field of the annular jet is related to the first two POD modes which correspond to a radial shift of the stagnation point. The modes 3 and 4 involve the stretching or squeezing effects of the recirculation region in the radial direction. In addition, the spatial structure of these four POD eigenmodes also shows the counter-rotating vortices in the streamwise direction downstream of the flow reversal region.

Automated summary

A three-dimensional incompressible annular jet was simulated using the large eddy simulation (LES) method at a Reynolds number Re = 8 500. The study focused on the flow dynamics of the wake flow, with particular attention to the proper orthogonal decomposition (POD) analysis of the velocity fluctuation vectors. The results showed that the first four eigenmodes captured significant turbulent kinetic energy, impacting the wake dynamics, with modes 1 and 2 related to a radial shift of the stagnation point, and modes 3 and 4 involving stretching or squeezing effects in the radial direction of the recirculation region.