Flow Dynamics of Unconfined Swirling Flames Under Fuel-Lean Conditions

This study provides the role of co- and counter swirl distribution in a experimental double concentric swirl burner that simulates the that simulates one swirl cup of a practical gas turbine combustor. Results of the effect of radial distribution of swirl in a burner under unconfined non-burning and combustion conditions are presented on the flow dynamics of a fuel-lean direct injection (LDI) configuration using propane as the fuel. Three-dimensional (3-D) flowfield data has been obtained immediately downstream of the burner exit to determine the detailed flow dynamics associated with the flow. The fuel was injected radially into the surrounding swirl flow. Flow characteristics, both without and with combustion, have been obtained for the co- and counter-swirl distributions to the combustion air flow under unconfined conditions. Flat vane swirlers have been used to induce swirl to the air flow. Both combustion and swirl distribution significantly influences the resulting flowfield. The resulting swirl number of the flow was calculated using the 3-D velocity data. Results show that swirl distribution in the burner and combustion provides significant effect on the characteristics of the internal and external recirculation zones. The heat release from combustion enhances the inner recirculation zone by increasing its width and length. Combustion causes significant increase to the velocity and vorticity magnitudes in the flow, and promotes flowfield symmetry. Combustion also affects the swirl number of the flow. The swirl number calculated from the geometrical relationships, derived from the swirl vane angle and swirler dimensions, is much different than that determined from the 3-D velocity field data. The entrained mass flow rate is larger for the co-swirl distribution case and this entrainment is further enhanced with combustion. The results provide the role of radial swirl distribution on the mean and turbulence characteristics of flows for the two different shear flow conditions between the inner and outer annulus of the burner.