Luca Francesco Caracciolo

The principal requirements of industry, with respect to the numerical simulation of gas turbine combustors, are computational efficiency and algorithm robustness, together with an accurate representation of the complex fundamental processes. This paper examines the performance of the premixed combustion models implemented in the commercial CFD package Fluent™, in order to validate the ability to model combustion in the context of a premixed gas turbine combustor. The predictions of the model are found to compare well with the experimental results available, demonstrating robustness and computational efficiency.

A modern lean burn combustor for propulsion application using a multi-swirler fuel injector system is studied under partially premixed combustion conditions. Combustion induced vortex breakdown (CIVB) plays an important role in establishing the near-field aerodynamic characteristics of lean burn fuel injectors, influencing fuel/air mixing and flame stability. The precise nature of the vortex breakdown can take on several forms mainly consisting of a precessing vortex core (PVC) and the appearance of multiple helical vortices formed in the swirl stream shear layer. In the present study a numerical investigation is carried out with an unsteady Reynolds-averaged Navier Stokes (URANS) solver to capture the evolution of the PVC in the vicinity of the air blast atomizer of the injector and the helical vortex patterns inside the combustor. PVC suppression is captured causing upstream flame propagation and a sudden rise in the temperature near the injector end. The existence of hot-spots is reported near the injector end which can increase NOx production and also cause possible damage to the injector assembly itself. The unsteady dynamics of the PVC, which significantly influences fuel efficiency and emissions, are analyzed for a relatively long period of real time. The variation of velocity along the axis of the combustor confirming upstream flame propagation in to the injector is plotted. Mass weighted average temperatures across different planes in the combustor are monitored as target functions. The influence of different time-step sizes on the prediction of the temperature across these different planes is also presented. For this lean burn combustor using a complex multi-swirler fuel injector system, the results demonstrate the formation of a startup PVC in the vicinity of the air blast atomizer of the injector, its unstable mode of excitation, sustainment and suppression due to CIVB over a period of time and its strong influence on injector near-field aero-thermodynamics.

Combustion noise may become an important noise source for lean-burn gas turbine engines, and this noise is usually associated with highly unsteady flames. This work aims to compute the broadband combustion noise spectrum for a realistic aeroengine combustor, and to compare with available measured noise data on a demonstrator aeroengine. A low-order linear network model is applied to a demonstrator engine combustor to obtain the transfer function that relates to unsteadiness in the rate of heat release, acoustic, entropic and vortical fluctuations. A spectral model is used for the heat release rate fluctuation, which is the source of the noise. The mean flow of the aeroengine combustor required as input data to this spectral model is obtained from RANS simulations. The computed acoustic field for a low-medium power setting indicates that the models used in this study capture the main characteristics of the broadband spectral shape of combustion noise. Reasonable agreement with the measured spectral level is achieved.