Effect of Mainstream Swirling on Flowfield Characteristics of an Outer-Cavity Trapped Vortex Combustor

Nonreacting flow characteristics are important for determining the performances of combustors. In the present work, the effects of mainstream swirling on the nonreacting flow characteristics of an outer-cavity trapped vortex combustor are investigated by introducing swirlers. The results are first validated by particle image velocimetry measurements by considering four swirl numbers (0, 0.4, 0.6, and 0.8) and three velocity sets. The results show that the addition of swirlers in the mainstream introduces 3D flow not only in the mainstream but also in the cavities. As the swirl number increases, the size of the low-velocity region near the center-line of the combustor increases both in the axial and radial directions. The cavity flow maintains the dual-vortex pattern for most cases; however, for certain cases with high mainstream velocities and high swirl numbers (0.6, 0.8), multiple-vortex patterns are observed. The mixing results are discussed in terms of turbulence intensity and kinetic energy. The turbulence intensities of the combustor outlet for a swirl number of 0.8 are found to increase by approximately 250-350% compared to the case without swirling, indicating dramatically enhanced mixing.