Impact of dynamic modelling of the flame subgrid scale wrinkling in large-Eddy simulation of light-round in an annular combustor

Abstract

Ignition of annular gas turbine combustors, also called light-round, is a challenging problem for aeronautic reliability and safety. Large Eddy Simulation (LES), based on massively parallel computations, has been already assessed as a reliable tool to analyse and predict such a phenomenon. The present study focuses on the effect of the flame subgrid scale wrinkling factor entering the combustion model. Large Eddy Simulations of the annular MICCA-Spray laboratory-scale chamber are performed with constant and dynamic strategies for the wrinkling parameter and are compared against experimental data. A bi-modal distribution of the model exponent during light-round is obtained with a different behaviour between the flames stabilized around each injector, and the flame fronts propagating in a circumferential direction. The impact of such locally defined and time-dependent evolution is analysed by studying several quantities associated to the flame propagation mechanisms. It is shown that the dynamic procedure entails a reduction of the wrinkling factor that is not balanced by an increase of the resolved flame surface. After considering the exhaust of burnt gases that affects the ignition in such a semi-confined system, the dynamic formulation leads to a moderate slowing down of the flame. Surprisingly, the sounder dynamic model does not yield better predictions of the experimental data, revealing the need to address other modelling improvements in the future. However, this does not temper the need for a dynamic combustion model in numerical simulation of light-round.