Numerical prediction of the formation of a recirculation zone and the flow mixing and combustion in a turbulent swirling flame.

Computations on a turbulent swirling diffusion flame with the recirculation zone were made based on the newly proposed combustion model and the modified k-εturbulence model. The modification was made taking the effects of the streamline curvature due to the swirl and the effects of the density gradient in radial direction into consideration. The turbulence model modification leads to the adequate prediction of the formation of the recirculation zone and mixing characteristics in the swirling flame. The prediction indicates that the recirculation zone promotes mixing even if the effective diffusivity is decreased due to the effects of the swirl motion and the density gradient. The retardation of mixing in the downstream of the swirling flame as compared with the cold flow is also well predicted. The combustion model proposed in this paper can predict the existence of the premixed fuel layer around the recirculation zone, and accurately predict the species concentration.