Transverse to longitudinal acoustic coupling processes in annular combustion chambers

Combustion instability is a major issue facing lean, premixed combustion approaches in modern gas turbine applications. This paper specifically focuses on instabilities that excite transverse acoustic modes of the combustion chamber. Recent simulation and experimental studies have shown that much of the flame response during transverse instabilities is due to the longitudinal fluid motions induced by the fluctuating pressure field above a nozzle. In this study, we analyze the multi-dimensional acoustic field excited by transverse acoustic disturbances interacting with an annular side branch, emulating a fuel/air mixing nozzle. Key findings of this work show that the resultant velocity fields are critically dependent upon the structure of the transverse acoustic field and the nozzle impedance. Significantly, we also show that certain cases can be understood from relatively simple quasi one-dimensional considerations, but that other cases are intrinsically three-dimensional.