The present paper describes a Large Eddy Simulation modelling framework for the simulation of oscillating flames in practical flow configurations. The unresolved sub-grid scale motion is modelled using the dynamic Smagorinsky model in combination with the Probability Density Function method. It is shown that the Large Eddy Simulation method is capable of reproducing the characteristic shape of the reaction zone as well as the non-linear evolution of the total heat release rate in a bluff-body stabilised combustor. Commonly used measures for quantifying the variation of the total heat release rate are evaluated and examined in the present flow configuration of a lean-premixed ethylene-air flame. It was found that formaldehyde-based measures do not appropriately reproduce the amplitude and phase of the total heat release rate. A significantly improved correlation was achieved by employing the product of the mass fractions of molecular oxygen (O2) and the ketenyl radical (HCCO) as a means of characterising the variation of the total heat release rate.