Vortical Structure of Reacting Flow in a Sudden-Expansion Combustor with Solid Fuel

摘要

This study investigates the vortical structure of nonpremixed combustion of solid fuel in a sudden-expansion combustor, which rarely been studied or discussed in the past. The mixing and combustion are dominated by the large-scale vortical structures, which are also affected by the dilatation effect introduced by reaction. Although the vortical structures in nonreacting flow resemble those in the premixed reacting case, a distinct pattern of vortices is observed for the nonpremixed reacting flow. The uniqueness is attributed to the distributed heat release typical of solid fuel combustion. Although small eddies merge into large-scale coherent structures in the nonreacting flow, they are essentially diminished in the nonpremixed reacting case, which is dominated only by large coherent vortices. Because of the existence of diffusion flame along the shear layer, intense interactions are observed among the vortices, which also enhanced the mixing between the oxidizing stream and fuel vapor. A linear increase in the vorticity thickness (slope ≈3.1) is observed upstream of the reattachment (x/h ~ 7) in the nonreacting case, whereas a large initial value with a slight decrease (slope ≈ -0.1) is revealed for the nonpremixed reacting flow upstream of the reattachment (x/h ~ 5). The results may benefit the understanding and advancement of propulsion systems with solid fuel.