28.05.2018 16:15 Camilo Silva (Fakultät für Maschinenwesen, TUM):
Nonlinear dynamics and combustion instabilities: an overviewMI 03.06.011 (Boltzmannstr. 3, 85748 Garching)

The reacting flow produced by turbulent flames is recognized as the main generator of acoustic waves in gas turbines and rockets (flame -> acoustics). Because modern gas turbines operate at lean regimes, the flame has become extremely sensitive to the surrounding acoustic field. Consequently, a two-way coupling may easily arise (flame <-> acoustics), which, if constructive, leads to the appearance of combustion instabilities. Combustion instabilities have been a constant nuisance in the design of gas turbines and rockets since their conception nine decades ago.

Combustion instabilities are generally studied by a divide and conquer approach: The relations ‘acoustics -> flame’ and ‘flame -> acoustics’ are characterized separately and, subsequently, combined in a unique model. Fundamental progress has been done in the last decades concerning the linear regime, i.e. when the aforementioned relations are linear. It is, therefore, possible to assess the stability of a combustor at a given (well-defined) operating condition by establishing whether a given initial acoustic perturbation will grow or decay.

Linear stability analysis is not sufficient for the conception of stable gas turbines and rockets within a wide-range of operating conditions. The acoustic field associated with limit cycles (combustion instabilities) and chaos (combustion ‘noise’) has to be consciously investigated and corresponding models developed. The present talk will give an overview of some relevant studies carried out during the last two decades on nonlinear dynamics and combustion instabilities.