SUMMARY

To satisfy stringent NOx emission restrictions, modern gas turbines have developed toward lean, premixed combustion systems, which introduces a new challenge called 'thermoacoustic instability'. This instability limits the turbine's operating conditions, reduces hardware lifetimes, and eventually destroys the combustor hardware. Therefore, the importance of understanding thermoacoustic phenomena in gas turbine combustors has increased sharply. This study focuses on azimuthal instability in a multi-nozzle can combustor. This azimuthal mode can be decomposed into two counter-rotating waves where they can either compete and potentially suppress one of them (spinning wave) or coexist (standing wave), depending on the operating conditions. To identify its modal nature (standing vs spinning), multiple pressure sensors must be installed around the circumference. This study first addresses the question of how to optimally locate the sensors for identifying the acoustic mode. With this sensor configuration, the study demonstrates the experimental results showing how the instability amplitude and modal nature vary with operating conditions, such as thermal power and azimuthal non-uniformities. As a final step, this study develops a low order modeling that captures important experimental observations. The contributions from each works are essential to monitor the azimuthal thermoacoustic instability, provide mitigation strategy, and develop a model for stability margin. We believe that the works presented here will be greatly beneficial to combustion systems experiencing thermoacoustic issues.