Modeling of complex physics & combustion dynamics in a combustor with a partially premixed turbulent flame

To avoid the formation of the high temperature stoichiometric regions in flames in a gas turbine combustor, and hence the formation of nitric oxides, an alternative concept of combustion technology was introduced by means of lean premixed combustion. However, the low emission of nitric oxides and carbon monoxide of the lean premixed combustion of natural gas comes at the cost of increased sensitivity to thermoacoustic instabilities. These are driven by the feedback loop between heat release, pressure and flow/mixture fluctuations. The pressure oscillations induced by thermoacoustic instabilities can reach very high amplitudes, possibly leading to severe damage and a significant reduction of the life time of the gas turbine engine. For this reason, it is important to be able to assess in the design phase already if a gas turbine combustor will have a stable flame at certain given conditions. To this end, tools and models for the accurate prediction of the amplitude and frequency of pressure oscillations are essential. The work presented in this dissertation focuses on the numerical modeling of the interaction between the coupled fields of flow, pressure and heat to predict the occurrence of self-excited high amplitude pressure oscillations. Calculations are done on a laboratory scale atmospheric combustion test rig, in conditions representative of gas turbine combustion systems, using three different approaches namely Fluid-only simulation (zero-way), Conjugated Heat Transfer approach (CHT) and two-way Fluid-Structure Interaction model (FSI). Each method addresses three important characteristics of flow: 1- The frequency of the oscillations, 2-Conditions under which the oscillations occur, and 3-The limit cycle amplitude.