EXPERIMENTAL-STUDY OF A MODEL GAS-TURBINE COMBUSTOR SWIRL CUP .2. DROPLET DYNAMICS

As the second part of a study to characterize the performance of a 3x scale gas turbine combustor swirl cup, the focus of the present articl e addresses the droplet dynamics. Droplet axial, radial, and tangentia l velocities as well as size were measured using phase Doppler interfe rometry. Bimodal droplet axial and tangential velocities distributions were observed in the shear layer close to the exit plane of the swirl cup. Bimodal droplet radial velocity distributions around the closing point of the on-axis recirculation zone and at the periphery of the s pray were observed as well. Droplet velocity histograms, based on drop let size classes, reveal how these velocity bimodal distributions are formed and explain why velocity fluctuations for larger droplets are g reater than those of the smaller droplets in some regions. Correlation s between size and velocity, individual velocity components, and size and flow angle provide evidence of intermittent flowfield structures s uperimposed on the local and global turbulence. Specific flowfield str uctures and flowfield intermittancies are found to give rise to these bimodal distributions. Overall, these data add measurably to the under standing of the two-phase transport that can occur in practical system s.