Simulation of turbulent swirl flow in an axisymmetric sudden expansion

The numerical simulation of the turbulent flows in axisymmetric sudden expa nsions with inlet swirl is addressed, with the focus being on the unsteady flow behavior. Numerical simulations using the Reynolds-averaged Navier-Sto kes equations closed via the k-epsilon turbulence model are presented. Resu lts fur an expansion ratio of 1.96 and a Reynolds number of 1 x 10(5) (at t he inlet) are presented for a range of swirl numbers from O to 0.48. The pr ecessing vortex core (PVC) and most of the features observed experimentally , including the precession direction, zero-frequency swirl number, and vort ex breakdown have been predicted. The calculated precession frequency for t he case of an expansion ratio of 1.96 is in close agreement with that repor ted in the literature. Moreover, a higher-order oscillation, in addition to the low-frequency PVC, has been predicted over a range of swirl numbers.