Response of unconfined vortex breakdown to axial pulsing

The response of unconfined swirling jets undergoing vortex breakdown to axial pulsing is explored experimentally. In particular, the combination of particle visualization and particle image velocimetry has enabled the effect of axial pulsing on the development of shear-layer flow structures and vortex breakdown to be quantified, as a function of both pulsing frequency and amplitude. A range of Reynolds and swirl numbers is considered. A key result is that application of low-level forcing at the natural frequency intensifies the shear-layer vortices considerably and results in a substantial relative downstream shift of the mean breakdown position.