Near-critical swirling flow in a contracting duct: The case of plug axial flow with solid body rotation

Rusak and Meder [AIAA J. 42, 2284 (2004)] recently studied the behavior of a near-critical swirling flow in a weakly contracting duct. We investigate the particular inflow condition consisting of plug axial flow with solid body rotation, and introduce a new perturbation expansion specifically suited to that case. We show that the wall recirculation occurring in the exit plane as a result of the nonlinear excitation of the critical wave by the weak contraction is more accurately predicted. We also compute the near-critical flow for strong contractions and show that wall recirculations trapped inside the duct are obtained instead.