This paper presents the effect of axial acoustic fields on swirl flows. Investigations were performed for pressure drop of 0.03 bar across the swirler, at the open end of a duct fitted with acoustic drivers at the closed end. The swirl flow field was characterized using particle image velocimetry (PIV). The swirl flow fields are altered with respect to the acoustic velocity oscillations in an acoustic cycle. The length of the CTRZ is shortened with increase in counter flowing acoustic velocity. The jets from the swirler vanes contract in co-flowing acoustic velocity and expand in counter-flowing acoustic velocity. The vorticity field of the swirl flow fluctuates in the presence of acoustic velocity oscillations. Copyright © 2009 by the American Institute of Aeronautics and Astronautics, Inc.