Thermo-Acoustic Properties in Combustion Chambers

Licentiatavhandling, 2010

Design and analysis methods for gas turbine combustors or afterburners have to be improved in particular regarding the prediction of combustion instabilites. A methodology, which combines the use of a linearized flow solver and an Arnoldi algorithm performing the eigenmode extraction procedure, resolves eigenmodes which are candidates to these instabilities. This thesis focuses on developing and validating three linearized solvers based on: 1) the Linearized Euler Equations (LEE), 2) the Linearized Navier-Stokes Equations (LNSE) and 3) the Linearized Unsteady RANS equations (LURANS) in terms of accuracy, CPU time requirements and robustness. The Validation Rig I combustor test rig is the experimental rig used for validating numerical results. Under certain conditions the rig is the stage of two well known combustion instabilities: the ''Buzz'' mode which has a frequency of about 120 Hz and the ''Screech'' mode which has a frequency of about 1200 Hz. Further studies are also carried out regarding the combustion models and the mode stability analysis which models the coupling between the aero-acoustic waves and the heat release fluctuations, the core mechanism behind the combustion instabilities.