Many rich dome gas turbine combustors currently in service use a pre-filming type air blast atomizer referred to as swirl cup to obtain efficient fuel-air mixing. In the present study, two phase flow inside the swirl cup is investigated experimentally to characterize the pre-filming and atomization process occurring there. The swirl cup geometry consists of two counter roatating primary and secondary swirlers, which is separated by a pre-filming surface called venturi. A simplex nozzle pivoted at the centre of the primary swirler generates the primary spray. The swirl cup geometry is modified by means of a glass venturi in experiments performed without the secondary air swirl, to provide optical access. Time-resolved volumetric laser induced fluorescence imaging is performed to visualize the flow field inside the venturi. It is found that hollow cone spray from the simplex nozzle is further atomized by the primary swirler air, and a majority of these droplets impact the venturi, forming a thin film. This film undergoes a spiral motion driven by the swirling primary airflow in the form of streaks. Further droplets impinging on the film causes splashing and disturbs the film motion. The film thickness variation along the venturi surface is statistically quantified from the PLIF images. At the venturi lip, the film and the streaks accumulate and are atomized by the shearing action of the two swirling air streams in the full swirl cup. The precessing vortex core of the primary air swirl imparts a precessing motion to the droplets, which dictates the non-uniform filming on the venturi. Phase Doppler Analyzer measurements are performed on different combinations of the swirl cup elements to identify the role of the individual air streams and the prefilmer in influencing the atomization. The aerodynamic flow field created by the swirling air streams considerably improves the atomization as compared to the pre-filmer in the present atmospheric tests. © 2015 International Conference on Liquid Atomization and Spray Systems. All rights reserved.