Modeling of combustion dynamics in gas turbine engines

This thesis describes a study of combustion dynamics in gas turbine combustors. The analysis consists of two parts: combustion response of a single premixed injector to longitudinal pressure disturbances, and three-dimensional flow simulations of a multi-element injector combustor under steady-state conditions.;In the first part of this thesis, the combustor under investigation is supplied with premixed air and methane through a single injector. Two approaches have been utilized to construct a systematic analysis for both steady and unsteady flow motions. A three-dimensional steady-state flow calculation is first conducted to form a basis for the analysis of unsteady flow motions. The formulation is based on the complete conservation equations with finite-rate chemical kinetics and is solved numerically using a preconditioning technique. The predicted flame shape shows good agreement with experimental observations. An approximate integral technique which incorporates the steady-state results is then developed to study the injector flame response to acoustic disturbances impinging from upstream and downstream of the combustion zone. The acoustic transmission and reflection properties of the flame region are obtained over a broad range of frequencies.;In the second part of this thesis, a complete analysis of the steady-state flowfield in a multi-element injector combustor is conducted. The combustor has four injectors and the entire flowfield is assumed to be azimuthally periodic. Results show that the primary difference in the overall flame structure from the single injector case is the presence of an additional flame anchored at the outer radius of the injector annulus, which merges with the flame anchored at the inner radius of the annulus. Results also show that the transport of hot product species from the recirculation zone of one injector to another may play a role in the ignition and maintaining stability of the outer flame.