Entropy and Vorticity Wave Generation in Realistic Gas Turbine Combustors

Understanding the nature of the unsteady flow at the combustor exit is required to accurately simulate time-dependent phenomena in the turbine entry, such as indirect noise generation. Using large-eddy simulations of the combustion process in a realistic geometry, the flow at its exit is analyzes. Two realistic near-ground certification operating conditions are considered. Different mechanisms for large-scale flow and thermal structure generation are described, which are ejected into the turbine. Modal decomposition methods are used to extract the spatial and temporal scales at the turbine entry. It is found that, depending on the operating condition, the entropy waves convect as elongated streaks in the core of the combustor annulus or the proximity of the walls. The dominant unsteady character of the fluctuations exhibits different spectral properties: that is, low frequency in the core and high frequency toward walls. At the combustor exit, the vortical field is dominated by the swirl in the air inlet, which is found to have little influence on the entropy perturbations. Furthermore, the importance of considering the interaction of multiple fuel injectors and combustion zones in an annular combustor is investigated. It is shown that pulsating circumferential vorticity modes can occur in multisector annular combustors, but these do not affect the entropy wave distribution.