Generalization of Turbulent Swirl Flame Transfer Functions in Gas Turbine Combustors.

Experimental investigations of the forced response of swirl-stabilized turbulent flames to upstream flow disturbances were performed in an industrial scale gas turbine combustor operating with natural gas fuel and CO2/air. We measured flame transfer functions (FTFs) for a wide range of forcing frequency over a broad range of operating conditions with 50–120 kW thermal power. A sensitivity analysis was then performed in order to identify the key dimensionless parameters controlling the forced swirl flame dynamics. Two different dimensionless parameters,St1 = (fδsw)/UandSt2 = (fLf)/U, are used as dimensionless frequencies, while the dependence of the FTF gain on the turbulent flame speed is taken into account using a dimensionless flame length, ξ = Lf/Dc. The implementation of the nondimensionalization strategy using several time and length scales reveals that all FTFs are well characterized by eitherSt1orSt2, but the best result is obtained from a combination ofSt1andSt2, which accounts for the interference mechanisms of vortical and acoustic disturbances in the system. As a consequence, the occurrence of local minima and local maxima, a clear manifestation of destructive and constructive interferences of acoustically forced swirl-stabilized flames, is well captured by the dimensionless numbers. This methodology is then applied to extensive FTF data measured from a different gas turbine combustor. A comparison of the FTFs for the two different gas turbine combustion systems provides insight into generalized transfer function behaviors in the dimensionless domain. This study focuses on velocity-coupled combustion instability, and these generalizations may not extend to situations where other coupling mechanisms dominate. [ABSTRACT FROM PUBLISHER]