Pressure oscillation in an industrial gas-turbine combustor is numerically investigated based on thermo-acoustic instability. The combustor has 37 EV premix burners through which methane and air are mixed and then injected into the chamber. First, acoustic eigenmodes and frequencies of the chamber are examined by adopting linear acoustic analysis. Next, combustion instabilities are simulated. In simulating instabilities, first, steady fuel/air mixing and flow characteristics established by the burner are investigated by numerical analysis with single burner. And then, based on the calculated flow data, the burners are modeled numerically via equivalent swirlers, which facilitates the numerical analysis with the whole combustion system including the chamber and numerous burners. Finally, reactive flow fields within the chamber are investigated numerically by unsteady analysis and thereby spontaneous instability is simulated. Based on the numerical results, scaling analysis is conducted to find out the instability mechanism in the combustor and a passive control method to suppress the instability is proposed and verified numerically.

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