Large Eddy Simulations of a lab scale single sector of a lean burn aero-engine combustor have been undertaken for both isothermal and reacting flows in order to examine the effect of combustion on the flow features and velocity fluctuations. For that purpose, use was made of the Rolls-Royce pressure based solver, PRECISE-UNS, to perform simulations. Unresolved sub-grid stresses were modelled by the Wall-Adapting Local Eddy-viscosity (WALE) model and combustion by the FGM model. The liquid-phase of fuel spray uses an Eulerian-Lagrangian approach, where the trajectories of a number of fuel droplets are calculated by stepping in time. Comparison is made with experimental PIV data at the exit of the combustor for mean velocities and velocity fluctuations. The analysis of the flow inside the combustor chamber showed the classical features of turbulent confined highly swirling flow under isothermal and as well as under reacting conditions. In fact, a large central recirculation zone on the x-axis and two corner recirculation zones were found. The effect of combustion in this study is to reduce the opening angle of the jet and as a result the size of the central recirculation zone is reduced while the ones at the corner of the combustor increases. Under isothermal conditions the occurrence of the precessing vortex core (PVC) was found at the frequency of ~ 82Hz with high amplitude. This produces regions with high velocity fluctuations. Under reacting conditions the PVC is damped and its frequency is shifted to ~ 95 Hz and its amplitude is considerably reduced. In term of velocity fluctuations, in general, results illustrated that, under combustion configuration they are considerably reduced resulting in low turbulence intensity.
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