Dynamics and Control of Flames Interacting with Pressure Waves

Abstract

The coupling between pressure waves and combustion gives rise to dynamical phenomena which constitute some of the most challenging problems in combustion research. A number of related issues have been investigated over the last decades. Studies have concerned fundamental aspects and practical implications. Important progress has been accomplished in the understanding, modeling and simulation of combustion dynamics. Detailed experiments have provided a wealth of information on elementary dynamical processes involving vortex interactions, mutual flame annihilation, flame collisions with boundaries, and coupling between flames and acoustics. The mechanisms driving instabilities and the coupling between pressure waves and combustion has been extensively investigated in gas turbine model combustors. Progress in numerical modeling has allowed simulations of dynamical flames interacting with pressure perturbations. This has allowed advances in prediction methods for combustion instabilities. Efforts have also concerned the development of the related subject of combustion control. A number of experiments on laboratory scale combustors have shown that the amplitude of combustion instabilities could be reduced by applying control principles and some applications of these principles have been made in full scale terrestrial gas turbine systems. Research has focused on algorithms, actuators, sensors and systems integration. In recent years, scaling from laboratory experiments to practical devices has been demonstrated with some success but limitations have also been revealed. After a brief review of the state of the art of these topics, this article describes some of our recent work on (1) Elementary processes in flame/acoustics coupling, (2) Simulation of combustion dynamics, (3) Multi-dimensional simulation of active control. Experiments on premixed flames responding to an acoustic modulation imposed on the upstream flow are used to illustrate fundamental interactions. It is shown that a flame impinging on a solid boundary and perturbed from upstream may induce a considerable amplification of the sound radiated by the system. The simulation of turbulent flames coupled to plane acoustic modes is then considered. The last topic is concerned with the numerical simulation of active control. This involves the coupling of a flow solver with a control algorithm. It is indicated that this coupling requires special precautions.