Effects of Flame Development and Structure on Thermo-Acoustic Oscillations of Premixed Turbulent Flames

Non-stationary confined premixed turbulent flames stabilized behind a bluff body are studied. A simple kinematic model of such flames was developed by Dowling [9] who reduced the combustion process to the propagation of an infinitely thin flame at a constant speed. The goal of this work is to extend the model by taking into account the structure of premixed turbulent flames and the development of turbulent flame speed and thickness. For these purposes, the so-called Flame Speed Closure model for multi-dimensional simulations of premixed turbulent flames is adapted and combined with the aforementioned Dowling model. Simulations of the heat release rate dynamics for ducted flames due to oncoming flow oscillations have been performed. Typical results show that the oscillations of the integrated heat release rate follow the oncoming flow velocity oscillations with certain time delay. The delays computed using the Dowling and the above approach are different, thus indicating the importance of resolving flame structure when modeling ducted flame oscillations.