This paper presents the behaviour of three very different and unique flame and flow structures within an atmospheric swirl-stabilised dump combustor supplied with a lean premixed mixture of methane and air. The reactant flow was artificially perturbed with frequencies of 100 Hz, 200 Hz, and 400 Hz. Phase average behaviour and temporal dynamics were characterised using phase locked high speed CH chemiluminescence and high speed stereo particle imaging. The interaction between the flame and flow field, in particular the internal recirculation zone of the vortex breakdown, was determined to be responsible for differences observed in behaviour at the three forcing frequencies. The 100 Hz perturbation frequency displayed simple oscillatory motion. Higher perturbation frequencies of 200 Hz and 400 Hz gave rise to a second toroidal vortex ring which formed within the internal recirculation zone adjacent to the inner shear layer. This caused additional out of phase modulation of the heat release rate and flame area. Twin counter rotating vorticity structures attached to the annulus were formed as a result of the chamber geometry. The oscillating inlet flow and oscillating reversed flow region of the inner recirculation zone caused oscillations in vorticity magnitude which were responsible for flame wrinkling and stretch effects upon the flame front. Vorticity within the shear layers was found to be the source of harmonic frequency generation of the imposed perturbation frequencies. The data is presented in detail to facilitate CFD model comparisons, particularly LES. Published by Elsevier Inc.