Vortex breakdown of the swirling flow in a Lean Direct Injection burner

This paper presents a comprehensive study of the unsteady flow field in a new concept lean direct injection gas turbine burner, which aims at a clean and efficient combustion with application to sustainable aviation and pollution abatement. Large Eddy Simulation (LES) and planar particle image velocimetry are employed to capture the characteristics of the swirling flow issued from the multiple-jet swirler under both the confined and unconfined conditions. The results are compared, and good agreement shows the capability of LES in capturing the large-scale flow structures. The iso-contour of axial and swirl velocities shows that the swirling flow is featured by multiple jets. These jets interact with the central recirculation zone (CRZ) and reform it into a "starfish" shape. Under the effect of the confinement, the flow displays a larger spreading angle of the jets and an outer recirculation zone (ORZ). A distinctive connection between the CRZ and the ORZ is evidenced to occur through the channels between the multiple jets. The outward flow in the channels is identified to oscillate at a Strouhal number of 0.1. To characterize the evolution, the unsteady large-scale structures, proper orthogonal decomposition (POD), and spectra POD (SPOD) analyses are performed. It is found that a single helix and a double helix are manifestations of two independent global modes in the SPOD analysis. The former shares the same frequency with the outward flow, and the latter is solely affected by the confinement.