Nonreacting flow experiments are conducted in a swirl-stabilized combustor with several configurations of a triple annular research swirler fuel injector. Particle imaging velocimetry is used to measure mean axial, radial, and tangential distribution of the velocity field, from which the swirl ratio and the position of vortex breakdown are calculated for each injector configuration. Numerical simulations based on the Reynolds-averaged Navier-Stokes model equations of nonreacting flows provide insight into the characteristics of the axisymmetric vortex breakdown phenomenon in a circular, finite-length pipe with a sudden expansion downstream of a concentric, circular inlet pipe. Results show that flow states with vortex breakdown can be simulated numerically. Good agreement is found between the results of the simulations and available theoretical predictions for the first appearance of breakdown downstream of the pipe expansion plane, as well as its first appearance in the inlet pipe section as the inlet swirl level is increased. Good agreement is also shown between the measured experimental data, simulations, and theoretical predictions. It is demonstrated that the theoretical criteria and numerical simulations can be used to predict the appearance and location of vortex breakdown for several different nozzles of varying swirl numbers relevant to the stability of lean, premixed combustion.

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