100 kHz PIV in a liquid-fueled gas turbine swirl combustor at 1 MPa

Simultaneous 100 kHz particle image velocimetry (PIV) and 10 kHz OH * chemiluminescence (CL) were used to investigate flow and flame dynamics in a liquid-fueled, swirl-stabilized, piloted burner operated at 1.0 MPa. The PIV measurements were focused on the inner recirculation zone (IRZ), which forms downstream of an annular bluff-body feature that separates the pilot and main reactant jets and plays a critical role in flame stabilization. The OH * CL images captured the large-scale flame structure and dynamics. For the operating condition studied in this work, a self-excited combustion instability was present and caused axisymmetric variations in flame length and global heat release at a frequency of 810 Hz. Dynamic Mode Decomposition (DMD) was performed on the measured velocity fields to isolate fluctuations associated with the thermoacoustic mode from other dynamic flow processes. The DMD results showed that the 810 Hz instability causes strong fluctuations of both the axial and radial velocity components within the shear layer between the pilot jet and IRZ, along with concomitant changes in the size and shape of the IRZ. The DMD spatial modes also revealed periodic generation of vortices within the pilot-IRZ shear layer at frequencies ranging from 4-5.5 kHz. Wavelet analysis was used to study the interaction between these smaller-scale flow structures and the large-scale flow-flame dynamics associated with the combustion instability. The frequency magnitude related to vortex shedding was shown to fluctuate with the 810 Hz instability. The peak frequency magnitude followed the maximum radial velocity in the shear layer, which occurs when the IRZ is at its farthest radial extent and the velocity gradients in the pilot-IRZ shear layer are the strongest. The characterization of cross-scale, flow-flame coupling in this highly turbulent, high-pressure flame was enabled by the state-of-the-art 100 kHz PIV measurements. (c) 2020 The Combustion Institute. Published by Elsevier Inc. All rights reserved.