A TWO-DIMENSIONAL CARTESIAN AND AXISYMlMETRIC.pdf

Source of Acquisition NASA Marshall Space fight Center A TWO-DIMENSIONAL CARTESIAN A N D AXISYMlMETRIC STUDY OF COMBUSTION-ACOUSTIC INTERACTION Caroline Hood2 and Abdelkader Frendi3 University of Alabama in Huntsville Huntsville, AL-35899 Abstract This paper describes a study of a lean premixed (LP) methane-air combustion wave in a two-dimensional Cartesian and axisymmetric coordinate system. Lean premixed combustors provide low emission and high efficiency; however, they are susceptible to combustion instabilities. The present study focuses on the behavior of the flame as it interacts with an external acoustic disturbance. It was found that the flame oscillations increase as the disturbance amplitude is increased. Furthermore, when the frequency of the disturbance is at resonance with a chamber frequency, the instabilities increase. For the axisymmetric geometry, the flame is found to be more unstable compared to the Cartesian case. In some cases, these instabilities were severe and led to flame extinction. In the axisymmetric case, several passive control devices were tested to assess their effectiveness. It is found that an acoustic cavity is better able at controlling the pressure fluctuations in the chamber. Introduction Environmental awareness leads to increased demands for the ultra-low emission engines. Lean premixed (LP) combustion is the most effective process for lowering the emission. As a result, the research and development of gas turbines, which use LP combustors, have been a major interest for the past two decades. Future gas turbine engines must provide ultra-low emissions and high efficiency at low cost while maintaining the reliability and operability of present day engines. The demands for increased performance and decreased emissions have resulted in advanced combustor designs that are critically dependent on efficient heyair mixing and lean operation. However, all combustors, but most notably lean-burning low-emiss