Swirler Design Parameter Impact on Lean Blowout, Pressure Loss, and Flame Liftoff

Swirl stabilized combustion is a common technique used in gas turbine engine combustors and is accomplished by introducing swirl into the inlet flow, which enhances mixing and stabilizes the combustion event. Coaxial swirlers introduce the fuel and air axially through concentric inlets and use vanes to impart a tangential component to either the fuel, air, or both flows. The present study conducted a parametric analysis of coaxial swirler design by manufacturing an array of 14 coaxial swirlers scaled for use in low flow, small engine operations which incorporated the same base design but varied the swirl number, S_n, by changing the vane angle between 0 deg and 63 deg, vane count between four and ten, and vane shape between traditional and helical. Each design was experimentally evaluated using nonpremixed air and propane at different flow conditions to correlate swirler design with lean blowout limits, pressure loss, and flame liftoff. Lean blowout was primarily influenced by swirl number, while vane count and shape had significant impact at S_n = 0.8 but little impact at S_n = 1.5. Pressure loss was unchanged below a S_n of 0.6, and unlike lean blowout, S_n had little impact at 0.8 but significant impact at 1.5. Additionally, an initial equation correlating pressure loss with swirler number, vane count, and mass flowrate was developed. Finally, flame liftoff was mainly driven by swirl number, with vane count and shape the next significant design parameters.