Structure of a swirl-stabilized spray flame relevant to gas turbine and furnaces

Abstract

To investigate the structure of a hollow-cone spray flame similar to those occurring in the primary zone of gas-turbine combustors or within furnaces, a swirl-stabilized combustor was used. A kerosene spray was produced by a simplex atomizer with a nominal included-cone-angle of 30 deg. Swirling air had a calculated swirl number of 0.36 and was produced by a swirl plate having an exit air velocity vector of 30 deg with respect to the chamber axis. A phase Doppler particle analyzer was used to measure drop size; mean and root mean square (rms) values of axial, radial, and tangential components; and drop velocity and size probability distribution functions (PDFs) at five different axial positions from the nozzle. A mean spray flame structure and terminology are proposed. It is found that a large portion of the drop flowfield within this spray flame is dominated by radial and axial components of the velocity vector. It appears that sufficiently away from the nozzle the direction of the mean droplet velocity vector is primarily established by the design of the swirl plate. Based on the bimodal behavior of drop axial velocity PDF, pulsation of the central recirculation zone is proposed and the extent of its effect on the droplet field is investigated. The rms of droplet flowfield is not isotropic in this spray flame. At each axial position, axial rms has the highest value among the three components and occurs near the maximum temperature point. Moving away from the nozzle near and along the locus of maximum mean temperature, strong preferential evaporation and/or burning of small drops drastically affect the shape of the size PDFs by progressively shifting its profile into larger size ranges.