FLAME HOLDING DYNAMICS DURING COMBUSTION INSTABILITY IN A SHEAR-COAXIAL INJECTOR COMBUSTOR
Combustion instability in an experimental high pressure shear coaxial combustor is studied using large-eddy simulation (LES) with a subgrid turbulent mixing closure. In order to match the acoustic mode excitation the entire rig is simulated and it is shown that the simulations reproduce the naturally excited instability in this combustor without any ad hoc adjustments. Two modes in the combustor are show to contribute to the instability and analysis of the flow-flame interactions shows that a triple flame structure exists in the combustor. This flame structure also undergoes a cyclic motion at the first excited instability frequency. Simulations are shown to capture the changes in the amplitude of the oscillation as the inlet duct length is changed. Results are analyzed to understand the nature of flame holding and its coupling to the acoustic modes in the combustor.
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