Combustion Dynamics of Swirling Flames
Event details
| Date | 27.03.2012 |
| Hour | 13:15 › 14:15 |
| Speaker | Sébastien Candel, Ecole Centrale Paris, France |
| Location | |
| Category | Conferences - Seminars |
Instability analysis of swirling flames is of importance in the design of advanced combustor concepts for aircraft propulsion and gas turbines for electricity production. A few of the many issues arising in such flows are considered in this seminar. It is first shown that the swirler plays an important role in the dynamics of the flow. Acoustic waves impinging on the swirler give rise to a convective vorticity mode inducing azimuthal velocity perturbations and swirl number fluctuations. This mode conversion process is briefly explained and illustrated by numerical simulations and validated with experimental data. It is then shown that the flame is submitted to a transmitted axial acoustic perturbation which propagates at the speed of sound and to an azimuthal velocity perturbation which is convected at the flow velocity. The net result is that the dynamical response and unsteady heat release are determined by the combined effects of these axial and induced azimuthal velocity perturbations. This can then be used to determine the flame transfer function. Results obtained from the model are in agreement with experiments. It is also shown that large eddy simulations of the perturbed swirling flame can retrieve dynamical features observed experimentally. Instability analysis of a generic combustor including a swirling flame is then investigated by making use of a nonlinear representation of flame dynamics relying on the describing function. In this framework, the flame response is determined as a function of frequency and amplitude of perturbations impinging on the combustion region. The flame describing function (FDF) is experimentally determined and is combined with an acoustic transfer matrix representation of the system to provide growth rates and oscillation frequencies as a function of perturbation amplitude. These data can be used to determine regions of instability, frequency shifts with respect to the acoustic eigenfrequencies and they also yield amplitude levels when self-sustained oscillations of the system have reached a limit cycle. The application of the FDF framework in a generic configuration indicates that this can be used in more general situations of technological interest.
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- IGM