Numerical Analysis of Isothermal Flow in Interacting Swirl-Stabilized Nozzles

The three-dimensional steady incompressible numerical results of an isothermal flowfield resulting from the interaction of two swirl-stabilized air nozzles in a multiple lean direct injection combustor configuration are analyzed. The spacing between nozzles S is varied from 1.1 to 2.72 nozzle diameters d to analyze the degree of swirl interaction between them and their impact on the resulting flow structure. The numerical results were verified by performing a grid dependence and turbulence model implementation study and validated by comparing them with time-averaged particle image velocimetry and unsteady Reynolds-averaged Navier-Stokes formulation data. The numerical solution resolves aerodynamic flow features typically associated with swirl-based combustion such as a form of vortex breakdown at the center of both nozzles and highly complex flow structures both upstream and downstream of the dome wall. Nozzle spacing has an important effect on the shape of the recirculation region and the flow velocities. In particular, interaction in the tangential velocity between the two nozzles has large effects on the swirl number and the size of the recirculation zone. Most of the changes in flowfield seem to be affected after the inner shear-layer jets of both nozzles have merged into a single jet flow in the axial direction. Two intermediate spacings (S = 1.36, 1.89d) exhibit unusual behavior in that the inner shear layers (towards the adjacent nozzle) are drawn into the center of the combustor, and a wide and low-velocity flow is created between the swirlers. This could be due to the inner shear-layer jets between adjacent nozzles not merging properly and behaving in a classical manner of two turbulent opposed planar jets.