Large Eddy Simulation of Combustion Instability of Low-Swirl Flames in a Multi-Nozzle Combustor

Large eddy simulation of self-induced combustion instability of low-swirl flames in a multi-nozzle combustor is carried out. The unsteady behaviors in the multi-nozzle burner including pressure fluctuation, velocity oscillation, PVC and triggering mechanism are studied in detail. Numerical result is compared with experimental measurement in terms of frequency and amplitude of pressure fluctuation. Results show LES successfully predicts the longitudinal instability mode in the multi-nozzle combustor with a reasonable agreement with experimental data. Flow parameters in the burner, such as pressure, axial velocity and CH₄ mass fraction oscillate with the same frequency but different phases. Combustion instability leads to flame flashback into the burner due to the reversal flow. Vortex generation and shedding off in the outer shear layer result in unsteady heat release at the tail edge of the outer flame near combustor wall. Meanwhile, the unsteady heat release feedback to the pressure and flowfield, which is the main reason for inducing combustion instability.