Shroud Influence on Gas Turbine Airblast Atomizer Swirler Flowfields

Abstract

The performance of high shear airblast fuel injectors for advanced gas turbine combustors is highly dependent on the design of the swirl vanes. The vanes may be of the straight or curved type. Curved vanes usually exhibit lower losses but straight vanes are also used due to lower cost and ease of manufacture. These type of vanes often operate under highly stalled conditions with high total pressure loss and a highly non-uniform exit velocity profile. This may produce poor fuel atomization with a non-uniform combustor fuel distribution resulting in lowered combustor efficiency and increased pollutant emissions. Constant turning curved vanes can also be easily manufactured. Properly designed vanes result in a greatly reduced total pressure loss. The exit velocity distribution is more uniform and higher in magnitude which can result in improved fuel atomization and distribution in the combustor. Further, the presence of a shroud is seen to have a major effect on the downstream flowfield. The present study compares standard helical flat vane performance with a low loss curved vane designed by the author for idle, and cruise conditions both with and without a shroud. The results from a three dimensional viscous numerical flow simulation show the curved swirl vane to be clearly superior to the standard flat helical swirl vane. The curved vane has a much lower total pressure loss with a more uniform exit velocity profile. This may result in improved combustor and engine performance and reduced pollutant emissions. The effect of the shroud was seen to reduce the size of the stall cell found in the vane passage for the helical vane. This resulted in a decrease in the magnitude of the axial velocity component in the outer vane passage and a decrease in the circumferential velocity component. This may result in a decrease in the swirl number. For the curved vane however, an increase in the magnitude of all velocity components was found which will result in a higher swirl number and better nozzle performance.