A large-eddy simulation model has been developed to study combustion instability in a ramjet combustor. A thin-flame model for premixed combustion is employed in the numerical scheme, which explicitly uses the local turbulent flame speed in the governing equation. Combustion instability in the ramjet has been numerically simulated. Two types of instability arc observed: a small-amplitude, high-frequency instability and a large-amplitude, low-frequency instability. Both such instabilities have been experimentally observed, and various computed flow features are in good qualitative agreement with experimental observations. The information obtained from these simulations has been used to develop an active control strategy to suppress the instability. Control of both types of combustion instability was successfully achieved using the acoustic feedback technique, and the control could be used to turn the instability on and off. The control is effective over a range of time delays, and the pressure fluctuation levels in the combustor are significantly reduced when active control is used.
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