Velocity Measurements in a Combustor Undergoing Limit-Cycle Pressure Oscillations

Abstract

Velocity measurements are reported in a swirl-stabilized spray combustor undergoing limit cycle pressure oscillations. The pressure-oscillations are a manifestation of the thermo-acoustic instability in the combustor (at 200Hz), and the goal of the present work is to understand the flow in a combustor with strong pressure oscillations. A second goal of the work is to provide data for the CFD modeling of self-excited combustion. The measurements have been made with a LDV for both the non-reacting case and the reacting flow case, and include velocity information for both the gas phase (with titanium dioxide seeding) and the droplet phase (no seeding). Measurements reveal substantial increases in the axial and tangential velocities under reacting flow conditions. The swirl-induced recirculation zone is much stronger (higher negative velocities) with combustion. Unburnt droplets are observed as far downstream as Z/Ro = 0.72 (nearly 5cm from the injection nozzle). Significant enhancements in the turbulence levels are noted in the presence of combustion, and these are partly attributed to the thermoacoustic instability and strong pressure oscillations.