Characterization of Forced Flame Response of Swirl-Stabilized Turbulent Lean-Premixed Flames in a Gas Turbine Combustor

Flame transfer function measurements of turbulent premixed flames are made in a model lean-premixed, swirl-stabilized, gas turbine combustor. $OH∗$⁠, $CH∗$⁠, and $CO2∗$ chemiluminescence emissions are measured to determine heat release oscillation from a whole flame, and the two-microphone technique is used to measure inlet velocity fluctuation. 2D $CH∗$ chemiluminescence imaging is used to characterize the flame shape: the flame length $(LCH∗max)$ and flame angle $(α)$⁠. Using $H2$-natural gas composite fuels, $XH2=0.00–0.60$⁠, a very short flame is obtained and hydrogen enrichment of natural gas is found to have a significant impact on the flame structure and flame attachment points. For a pure natural gas flame, the flames exhibit a “V” structure, whereas $H2$-enriched natural gas flames have an “M” structure. Results show that the gain of M flames is much smaller than that of V flames. Similar to results of analytic and experimental investigations on the flame transfer function of laminar premixed flames, it shows that the dynamics of a turbulent premixed flame is governed by three relevant parameters: the Strouhal number $(St=LCH∗max/Lconv)$⁠, the flame length $(LCH∗max)$⁠, and the flame angle $(α)$⁠. Two flames with the same flame shape exhibit very similar forced responses, regardless of their inlet flow conditions. This is significant because the forced flame response of a highly turbulent, practical gas turbine combustor can be quantitatively generalized using the nondimensional parameters, which collapse all relevant input conditions into the flame shape and the Strouhal number.