Abstract Swirler design strongly influences combustion stabilization and flame dynamics in gas turbines. The rotating flow induced by the swirler is mainly determined by the swirl number. While empirical formulas may be used to estimate this quantity and deduce the corresponding flow features, a precise quantification of the impact of geometrical details is not available. This issue is investigated in this article by analyzing the sensitivity of the mean flow field and unsteady structures to small changes in the swirler design. Two radial swirlers, with slightly different geometries are compared by combining Large Eddy Simulations and experiments. The geometrical difference induces changes of the mean velocity components near the injection plane, which in turn modify the structure of the internal recirculation zone. Effects on the precessing vortex core are then revealed by applying a dynamic mode decomposition to the numerical results. It is found that the geometrical modification of the swirler notably affects the flow structure and PVC frequency.